Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert.

By The Numbers - October 2005 edition

This time-worn phrase is familiar to us and it an appropriate term to apply to the HVAC service business.

Service technicians must be proficient in the use of service tools and measurement instruments such as multi-meters, U-tubes, manometers, voltmeters and so on. The proper use of these tools will enable the technician to professionally diagnose and repair problems, and do so in a professional manner that earns continued customer loyalty.

Would you like to know how proficient your techs are at using these (expensive) tools? At your next service meeting, challenge then with this short quiz so you can see where your tech’s strengths are, and where you need additional training.

Mr. Control Pro Quiz: Using Meters on Service Calls

Question #1:
Honeywell intermittent gas ignition devices are the most common types used among all manufacturers. They recommend that a properly adjusted pilot – steady, non-wavering – flame should produce (with main burner off) a flame signal of:
A. .2 amps
B. 132 volts
C. .000002 amps dc
D. 18-30 millivolts
E. 175 ohms

Question #2:
What is the proper output voltage (without a load) of a NEMA rated 120/24 volt AC step down transformer?
A. 24 VAC
B. 26-32 millivolts
C. 120-124 VAC
D. 261/2 +/- ½ VAC
E. 18-32 volts

Question #3:
New, standard purpose single thermocouples, in order to meet code requirements, must open the main valve circuit in no longer than _____ (seconds, minutes, hours) on a loss of pilot flame?
A. 180 seconds
B. 15 seconds
C. 2 minutes
D. Right quick
E. 60 seconds

Question #4:
The “cad” cell (oil) output reading on a normally adjusted gun type, high pressure oil burner should read:
A. 1600 to 2500 ohms
B. 16 to 25 ohms
C. 300 to 1000 ohms
D. 2150 to 2175 ohms
E. 1200 to 1500 ohms

Question #5:
Standard, direct burner ignition, Norton ignitors (silicon carbide) are typically used on both White Rogers and Honeywell ignition systems. They are powered with 120 VAC for either _____ or _____ before testing for flame recognition of main burner.
A. 60 seconds or 120 seconds
B. 17 seconds or 34 seconds
C. 4 or 7 seconds
D. 3 minutes or 5 minutes
E. 11 minutes or 4 minutes


Correct Answers are:
1. C
2. D
3. A
4. C
5. B

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net
 

By The Numbers - November 2005 edition

The HVAC service business can be a "numbers game". In this month’s article we’ll take a look at how we can follow the numbers when servicing or troubleshooting gas burner Intermittent Ignition Systems.

Most systems in use today use the principle of Flame Rectification to prove the presence of the pilot flame. Here is the typical sequence of operation:

# 1 - The pilot flame is a conductor of current - just like a copper wire - except it's resistance is extremely high. When metered, you will see a natural gas pilot flame measuring on the order of 11 to 12 meg ohms.

# 2 - The surface area of the flame sensor (flame rod) in the pilot flame must not exceed 1/4 of the total ground area ( including the pilot burner hood , pilot burner ground straps , etc.. ). This ratio is critical in order for an A/C signal to be rectified into a pulsating D.C. signal .

# 3 - The D.C. signal in the circuit must, in almost every system, equal or exceed 2 micro-amps (.000002 ) for the control module to operate properly . A steady signal of 2 or more microamps will produce reliable operation. A wavering signal (from less than 1 microamp to 2,3,4 5, or more ) will produce nuisance shutdowns. These signals are generally caused by drafts across the pilot flame or main burner flame impingement on the pilot burner assembly. A drop in signal strength below 1.6 microamps for .8 of a second will cause nuisance shutdowns or lockouts. A high percentage of those systems operating today will automatically recycle after 5 minutes however older systems require manual resetting. This can be done by either killing power to the system transformer or lowering the room temperature on the thermostat for approximately 1 minute before resetting it to the normal temperature.

#4 - Other areas of concern are :
 
A - Cracked ceramic flame rod holders
B - Bent or misaligned pilot burner brackets
C - Partially clogged pilot orifices or main gas valve filters
D - Contaminate build-up on flame sensors
E - Shorts in the flame sense circuit caused by scale from the heat exchanger or main burner

Probably the most common problem is a BAD GROUND CONNECTION TO THE SYSTEM. QUICKLY CHECK THIS BY CONNECTING A JUMPER WIRE FROM THE PILOT BURNER BRACKET TO THE BURNER GROUND CIRCUIT CONNECTOR ON THE SYSTEM MODULE. IF THE SYSTEM FUNCTIONS NORMALLY, YOU SIMPLY NEED TO PROVIDE A BETTER PERMANENT GROUND.

This is a " Readers Digest " version of just some of the numbers your techs need to be familiar with in order to service Intermittent Ignition Systems in the field today.
 

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net



By The Numbers - December 2005 edition


Smart Valve Gas Ignition Systems #1

This month’s article will be the first of several that will deal with the specifics of numerous varieties of the "Smart Valve" gas burner ignition system. In excess of 4.5 million of these systems are in use today on equipment as diverse as residential gas furnaces, roof top packages, domestic water heaters and deep frying equipment built by a large number of different manufacturers.

Smart Valve Gas Ignition System Overview

• All Smart Valves eliminate the need for a separate device, remotely mounted, that contains the electronics necessary to control the sequencing of the pilot, the main gas burner and flame sensing circuit. All of these functions take place in the valve’s operating head.

• Each of the many varieties of this Smart Valve system use flame rectification for flame proving .

• All of the system’s electrical wiring occurs on the valve’s top using Amp-type electrical connectors to plug in to receptacles on the valve (except on Generation I systems, which have the 4-pin power receptacle located on the valve’s gas outlet face).

• All of the different low voltage systems use Norton’s 24 VAC type silicon nitride igniter. This igniter has a low starting resistance to current flow and it heats to the temperatures needed in +/- 2 seconds. As its temperature rises its resistance increases.

• Smart Valve systems that use line voltage igniters require Norton igniters that need from 7 to 17 seconds for proper warm-up prior to allowing main gas to flow. These igniters are a version of silicon carbide. These have a higher initial resistance to current flow but it reduces as it heats .

• All valves (with exception of Generation 1 valves) have an electrical on-off switch located on the valve’s top . This interrupts current flow to the valve’s pilot and main gas valve. It is also the replacement for the older style units that utilize gas rotary shut off gas cocks .

• These systems are not suitable for equipment retrofit on older appliances. They can only be applied by the appliance manufacturer.

• These systems have a maximum gas capacity of 415 cfh - depending on the valves inlet and outlet sizes. It is important to note the valve’s capacity must be reduced by 5% if a screen-type filter is used in the outlet of the valve .

• Basic versions will provide a communications link to the equipment 's electronic fan timer to start the "Start-On delay and Fan-Off delay" timings. This signal is provided through a 16 VAC signal to the EFT carried by a lead in the 4-pin plug that supplies the 24 VAC power to the valve from the EFT.

These are but a few of the unique system properties that must be understood by your technicians so that they may provide excellent service to your customers that own equipment with Smart Valves "

Feel free to email me with any questions you or any of your co-workers might have.

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net



Pressure Regulating Gas Valves - January 2006 edition


In last months article we reviewed a number of differences between Honeywell's "Smart Valve" gas ignition control system and conventional intermittent ignition gas burner control systems.

The techniques and skills used to service Smart Valves are the same or very similar to those already being used to service standard systems. This article will focus on the Pressure Regulating Valve (PRV) components that are part of the gas valve/ignition control system.

The gas pressure regulator's purpose, whether it is a functional component of the control valve, or a separate entity, must control the gas pressure (natural or L.P.) to the main gas burner. The gas utility provides a main (service-pounds to inches) regulator to the residence or building from which all of the building’s gas needs are to be met. Generally, the goal is to supply natural gas at 7" water column (W.C.) at the outlet side of the regulator. On occasion this may not happen. In extreme cases where the weather is severe and/or the customer is toward the end of the gas line, the available pressure, because of capacity issues, may actually be lower than desired.

Most gas burning appliances are designed to operate on 3.5" W.C. on natural gas ( 11.0" W.C. on propane). One thing is certain - THE GAS VALVE REGULATOR CANNOT RAISE THE INLET PRESSURE TO THE MAIN BURNER ABOVE THE INLET PRESSURE TO THE VALVE. When the technician checks gas pressures he/she should have all of the buildings appliances operating at full capacity.


It is important to note that over 95% of all combination gas valves DO NOT regulate the pressure of the gas to the pilot outlet. When you adjust the pilot adjusting screw, you are changing the flow rate - not the pressure - and you are basically changing only the pilot gas flame size. It is important to keep the pilot flame steady, (not like a torch) and in constant contact with the pilot burner hood for good pilot fame recognition in the sensing circuit. The pressure of the pilot gas will be the pressure of the gas at the valves inlet minus the pressure drop through the valve. On average, you could see 6.0 to 6.2" W.C. when you have 7.0" at the valves inlet (natural gas)

Troubleshooting Tips
# 1. - Each valves capacity is partially a function of the valves inlet and outlet dimensions, and the regulators range of pressures that it can safely operate. The valves complete model number will provide the information about its capacity, the regulators range of pressures it can provide and other special features the valve may include.
# 2 - Any time you find it necessary to replace a gas valve it is a good technique to, after replacing the valve, check the outlet pressure to the main burner, To insure that you do not overfire or underfire the burner (sooting, not enough capacity to meet the spaces requirements, tee..) always check the appliance’s rating plate and check to see the regulator is set correctly.
# 3 - You may change the regulator’s output by removing the cap screw and repositioning the underscrew. Turn the underscrew CLOCKWISE for RAISING the set point and turn the underscrew COUNTER CLOCKWISE to REDUCE the set point.
# 4 - All combination gas valves have outlet pressure taps for measuring outlet pressures and only Honeywell provides an inlet pressure tap for ease of getting inlet pressure readings .
#5 - A few valves (including Smart Valves) have outlet screens (filters) - in such event, these filters will reduce the output capacity by 5%. Most valves have additional filters imbedded in the body of the valve to protect the pilot gas passages and these are not replaceable in the field.
#6 - If the inlet gas pressure to the valve (including Smart Valve) is in the valves nominal range (consult the valves specification sheet) and you cannot provide the correct capacity / pressure to the main burner - you should replace the valve.

Next Month: More on Smart Valves and their control and servicing.

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net

Operating Principles and Troubleshooting of Honeywell Smart Valve - February 2006 edition
As promised in last month’s Sales Bytes, this issue will focus on the Operating Principles and Troubleshooting of Honeywell Smart Valve gas control systems for residential type gas burning equipment.

Let’s start with the Operating Sequence.

The operating sequence of Smart Valve gas ignition and control systems is very similar to the older style, intermittent ignition systems which incorporate remotely mounted spark ignition modules. Those older systems use a 12,000 to18, 000 DC voltage source for ignition of the pilot gas. The Smart Valve system uses a 24 VAC powered hot surface pilot gas igniter to ignite the pilot gas. The main gas is ignited in both instances by a pilot gas burner.

The Smart Valve system is self-contained, thus eliminating the need for a separately mounted ignition source, usually in the furnace or boiler vestibule.

Starting with a call for heat from the thermostat, the circuit usually (not always) will be completed to the R and W terminals located on an Electronic Fan Timer (EFT). A separately mounted 120/24 VAC transformer supplies power to the entire control circuit. Immediately the EFT energizes the induced draft fan. As quickly as the Air Proving Switch (APS) senses that there is a proper amount of draft air moving through the combustion chamber, the APS closes its switching contacts in order to complete the circuit to the Smart Valve. As the circuit is completed, the igniter is powered and the pilot gas valve is opened with the igniter lighting the pilot gas. In those systems using an EFT the Smart Valve sends a 16 VAC signal to the EFT to start the time delay which dictates the amount of time that must pass prior to energizing the air handling blower.

The flame rectification / proving system proves the pilot flame is lit (in less than 2 seconds) and allows the main fuel valve to open and to simultaneously shut down the igniter. The flame proving system continues, monitoring only the pilot gas flame. The main fuel valve remains open until the call for heat ends. In those instances where some problem exists, the operation includes a 90 second Timed Trial for Ignition. If the system has not proven the pilot flame in 90 seconds of trying to prove the pilot, the system will shut down (not lockout) for 5 minutes and then will go through the starting sequence again. The system will go through this sequence until either the call for heat is ended or the burner lights off successfully.

Once the call for heat is completed, the EFT starts the timing cycle (field adjustable) to allow the air handler to complete the blower-on timing.

The above sequence applies to SV9X00 and the SV9X01. The SV9X02 includes a pre-purge timing (15 or 30 seconds) and the SV9X03 includes a lockout after one attempt to light-off.


TROUBLESHOOTING SMART VALVE SYSTEMS

The steps to correctly troubleshoot Smart Valves are as follows:

#1 - Shut off the flow of gas to the appliance in question with the ' A ' cock.

#2 - Make certain that the gas cock, located on top of the SV9X00 family of Smart Valves or later generations of Smart Valves SV9X01, SV9X02, SV9X03 which include an electrical slide switch (replaces the rotary gas cock) are placed in the Open or on position.

# 3 - Unplug the 2 x2 system harness plug located on top of the valve operating head.

# 4 - Make certain there is 24 VAC available from the system’s control circuit transformer. The transformer MUST be a minimum 40 VA (NEMA) rated. Such systems as SV96XX must have 50 VA NEMA-rated transformers at a minimum.

# 5 - Measure for output voltage at the 2 x 2 connector for 24 VAC between the 24 VAC common connector pin (Locate the proper pin locations in the Smart Valve instruction sheet) and the 24 VAC power source pin from the thermostat and/or air proving switch. There should also be 24 VAC between the 24 VAC common connector pin and the 24 VAC connector pin. (Note - there must be 2 pins powered for the system to operate. (One is constantly powered and one powered through the thermostat and/or air pressure switch).

# 6 - Plug the 2 x 2 wiring plug to the 2 x 2 wiring receptor. With 24 VAC present on the 2 receptacle pins the system will be energized. A 2-3 second delay will occur in the start up to allow the system to self check its electronics for a flame simulating component failure (If a component should have failed it will not continue to operate.)

After this delay the ignition sequence will begin in the SV9X01 and SV9X03 systems. The SV 9X02 has a pre-purge delay of either 15 or 30 seconds - OEM's choice.)

#7 - The silicon nitride 24 VAC igniter should begin to heat and in 1 to 2 seconds glow red. If the igniter fails to glow to incandescence and you have the proper voltage present (19.5 - 26 VAC) - replace the igniter if the nominal voltage is not present to the igniter - replace the Smart Valve.

# 8 - If the igniter, which is part of the pilot burner assembly (Q3450 or Q3480) glows red, turn the main gas supply gas cock back to the open position. The pilot gas should ignite. If not confirm that gas is present in the piping system, that all of the air has been purged from the pilot gas line (all the air must purge the pilot gas orifice.)Make certain a call for heat still exists - if the pilot gas does not ignite at this point replace the Smart Valve. Please note that all of the ignition module components are contained in the gas valve and the entire Smart Valve must be replaced.

If gas flow is present to the igniter and ignition doesn't occur measure for voltage between the 24 VAC common connector pin and the 24 VAC hot pin. If a nominal 24 VAC (19.5 to 26) is not present check the 24 VAC transformer output and replace the transformer with a properly sized, NEMA rated transformer (required for warranty purposes.) If you have the proper voltage to the igniter and it does not glow replace the igniter with a replacement igniter/flame rod assembly Q3400A1024. The igniter and flame rod must be replaced at the same time - they are combined into a one piece assembly and are packaged with a new stainless- steel spring mounting clip. This one unit fits both the Q3450 and Q3480 pilot burners.

# 9 - If the main burner does not light after the pilot has ignited and the igniter has been de-energized:
A. - Make certain that the pilot flame and the flame rod are making good contact.
B. - Check that the pilot burner bracket is not misaligned or bent from its original position
C. - Use a gas pressure reading instrument (i.e... Manometer etc... ) to check for proper inlet gas pressure. There is an outlet gas pressure tap on the outlet side of the gas valve for this measurement - there is also an inlet pressure tap as well. For natural gas systems, the pressure required is normally #.5 inches of water column however check the appliances Manufacturers rating plate to verify the pressure needed on this unit for correct firing
D. - Inspect the pilot orifice or clogging or apparent damage. If necessary, replace the orifice - DO NOT attempt to drill out the orifice.
E. - Check the electrical system for a good system ground through the pilot burner gas tubing ' You can use a jumper cable (with alligator clips). Connect one end of the cable to the pilot burner bracket and the other end to the gas valve - if the system then operates, you have isolated the problem to a bad or insufficient ground.
F. - If none of these checks surfaces the system problem then replace the ignition assembly (Q 3400 a 1024) At this point the system should operate properly - if not - replace the Smart Valve.

TROUBLE-SHOOTING TIPS.

To correctly diagnose system problems in Smart Valve products you should have a digital multi-meter or a analog meter - either of which should be able to measure one tenth of a micro amp ( .0000001 amps / dc. )The meter should also read ohms resistance down to one tenth of one Ohm (.01)

AA. - The resistance of a Norton silicon igniter used in the Q3450 or Q 3480 pilot assemblies, when new and cold, will be between 3 and 4 Ohms (average 3.7 Ohms) as the igniter ages the resistance will increase. When its resistance reaches 10 Ohms the igniter should be replaced

BB.-.A test harness for use in making micro amp readings while the system is working is available through your Honeywell distributor - the part number is 395466 .Smart Valves - Generation 1 will need a minimum reading of .0000003 micro amps (Three tenths of one micro amp) Generation 1 systems can be easily identified by the rotary gas cock knob on the top of the valve. It will also have part numbers SV 9500 or SV 9600 Generation 2 systems or later can be identified by an electrical slide switch on top of the gas valve. This slide switch electrically opens or closes the gas flow circuit in the valve and replaces the rotary gas cock. Generation 2 valves are the direct replacement for both generation 1 and 2 valves .This test harness also will allow you to easily convert micro amps to kilovolts. The minimum value you want for a microamp reading on generation 2 systems is 2 (.000002 A). Most importantly is the need that the microamp signal, on either system, be a steady signal. A wavering signal indicates that the pilot flame is not playing on the flame rod steadily - the flame recognition time is less than 2 seconds - and nuisance shutdowns will occur. Check for drafts across the pilot burner .

In following issues of Sales Bytes we will discuss older Intermittent Ignition Systems.

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net

Operating Principles and Troubleshooting of Older Intermittent Ignition Systems - March 2006 edition

In last month’s Sales Bytes, we focused on the Operating Principles and Troubleshooting of Honeywell Smart Valve gas control systems for residential type gas burning equipment. Now we’ll look at older Intermittent Ignition Systems.


There are in excess of 24 million electronic intermittent ignition controls systems in operation today. Each uses a separate ignition module remotely mounted in the appliance. Its job is to sequence the source of ignition and control the main fuel valve. Honeywell, in both OEM as well as the trade version for universal replacement, has historically provided the bulk of these units to the residential and light commercial markets.

The most significant difference in troubleshooting these ignition systems is in the flame sensing circuit. Once that is mastered, troubleshooting the rest of the system is very similar to even older standing pilot systems.

To illustrate what you need to do we’ll use the Honeywell S8610U intermittent ignition control module. This is a universal control module that will replace over 300 Honeywell and competitive devices. This package includes the module, valve, ignition hardware and cables necessary for the complete replacement.

Troubleshooting Honeywell’s S8610U Ignition Control System

1. Turn off the power supply to the appliance. Set the thermostat to call for heat. Check for 24 VAC to the module. You’ll need to check at the TH-TW terminal and at the 24 VAC terminal if an automatic vent damper is installed to the damper connector.

a. If POWER IS NOT PRESENT check the low voltage transformer output, then the limit contact for closure, then the thermostat to confirm it is calling for heat. You may also need to check any air proving switch(s), the vent damper (confirm it is open), and that the vent damper end switch is closed.

b. If POWER IS PRESENT then check for a spark across the igniter / sensor gap. If there is NO SPARK, pull the ignition lead and check for spark at the ignition stud or terminal. Vent Damper Alert: Make certain that a vent damper had NOT previously been installed and cycled. There is an ANSI standard that required an internal fuse to open when that happened to ensure that, in that case, the vent damper was always installed and operating properly.

c. If a SPARK IS PRESENT when you test at the stud / terminal:
i. Check the ignition cable, ground wiring, the ceramic insulator and the gap on the ignitor (should be .125 inches). If in doubt, replace the component.

d. If SPARK IS PRESENT when you initially check the ignitor gap and then it stops, turn off the gas supply and start the sequence over again.

2. Does the pilot burner light?

a. If the PILOT DOES NOT LIGHT then check all the manual gas valves are open, that the supply tubing is not kinked, that inlet pressures are good and that the pilot burner orifice is not plugged.

b. Also check the electrical wiring to the gas valve’s pilot terminal (PV). You should see 24 VAC across the PV-MV/PV terminal on the module. If OK, replace the gas valve. If NOT OK replace the S8610 module.

c. When the pilot burner lights, does the spark shut down? If the spark DOES NOT SHUT DOWN check the ignition cable’s continuity and the ground contacts.
i. Connect a jumper cable between Terminals 4 and the pilot burner bracket. If the system works correctly then the problem is a bad ground. A 2 microamp signal (steady) is the minimum you want to see.

d. Flame rods need to be clean. Use s very, very fine burnishing cloth to clean them if needed.

e. Check for cracked ceramics. This will eventually cause a leak to ground.

f. Adjust the pilot flame so that it covers the flame rod and is steady and blue. The flame must be shielded from any drafts.

g. If the SPARK SHUTS DOWN WHEN THE PILOT LIGHTS does the main burner light? If the main burner does not light check for 24 VAC across the MV-MV/PV terminals. If power is present, replace the valve. If power is not present, replace the module.

3. Other checks

a. High temperature on the ceramic insulator can cause signal leakage to ground. Temperatures should be less than 1600F.

b. While the system is running remove the cable from the MV terminal. The gas valve must close. If not remove and replace the valve.

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net

Questions from the field - April 2006 edition

Some good questions have come to me this past month and I’d like to share the replies with all of you.

What method do you recommend that we use to measure the micro-amp circuit value output in older individual component, electronic intermittent ignition systems?

Several questioners were inquiring about the Honeywell S 8610 family of electronic ignition systems. First of all, you must use an accurate ammeter (or multi-meter) that will permit readings in micro-amps (.000001) the specification sheet for the module you are testing will generally indicate that a minimum reading of 1.2 microamps is required. This statement is accurate, however, in actual field installations, a reading of that magnitude will produce numerous nuisance shut-downs .The reason for that is the " flame failure response " time is so fast - less than . 8 seconds - that any thing that can cause the pilot flame to drift, if only momentarily (drafts, clogged pilot burner orifices, low or fluctuating gas pressure etc...), will cause the system to go through the start cycle all over again. The “timed trial for ignition is 90 seconds. If you have not proven the pilot in that length of time the system will shut down for 5 minutes and then restart the cycle all over again. That process will continue until the thermostat is satisfied or the power is turned off.

When testing the micro-amp signal you should remove the low voltage lead to the main fuel valve- either on the " MV " terminal on the gas valve or the ignition module .If you allow the main valve to operate during the test period the main burner flame may / will impinge upon the pilot burner bracket / or pilot flame and will increase the micro-amp output which will give a false reading. While many pieces of literature will indicate that you may achieve a reading of up to 10 micro amps this really only happens in the test labs, I believe. In real world applications, a steady (no wavering of the pilot flame or fluctuating of the meter reading) 2 to 5 microamps will provide reliable performance
The meter should (like any amp measurement) should be placed in series with the load. In the case of testing the S8610U module the meter should be placed in series with the burner ground lead. The module is labeled “Burner Ground”

The hot surface igniter (HSI) used on direct burner ignition systems appears similar to the material used in “Smart Valve " systems. The line voltage igniter normally has a long warm-up time of either 17 or 34 seconds before the main fuel valve may be opened for main burner light -off. Why does the igniter used with “Smart Valve “systems light up so quickly in order to ignite the pilot?

The two igniters, while similar in appearance, are made of different alloys. The Norton igniter models 201 and 271 are made of silicon carbide while the Norton igniter used in “Smart Valve “low voltage gas burner ignition systems are comprised of silicon nitride and additional compounds.

The Norton 201and 271 igniters have line voltage - 120 Vac - applied to them and they have a high initial resistance to current flow - thus the long warm - up timing. The resistance reduces as the igniter warms The Honeywell pilot burner family (Q 3450) used in “Smart Valve " systems utilize a combination flame rod / igniter in a fixed bracket that is held in place in the pilot burner bracket with a stainless spring clip . . If either the fame rod or igniter must be replaced both must be replaced. The igniter has low initial resistance to current flow- it heats up quickly - less than 2 seconds- to provide ignition to the pilot gas flow which is energized at the same time as the igniter is energized .The resistance value of the igniter - when new and cold will be between 3 and 4 ohms . The resistance of the igniter increases with use and time. Replace it when the resistance gets to 10... On series 2 “Smart Valves “the minimum micro amp reading should be 2, on series 1 systems the minimum should be .0000003. (.3 micro amps.)

Next month we will review low voltage -step down transformers. - Application and sizing.


Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net

Questions from the field - June 2006 edition

OIL BURNER PRIMARYS

Oil burner primary controllers are classified into two specific groups - thermal (heat sensing) and optical sensing. Both of these groups also are separated into two different types of ignition providing devices - Intermittent Ignition and Interrupted Ignition.

Intermittent Ignition-- (Previously - pre 1964 were called Constant Ignition) The igniter is powered when the burner is powered and will remain energized as long as the burner is powered. The ignition and the burner normally are powered form the same contact on the primary control.

Interrupted Ignition -- (Previously - pre 1964 were called Intermittent -- changes mandated by U.L.) the igniter comes on when the burner is energized. The igniter will shut down automatically when flame has been established or after a pre-determined period of time has elapsed.
Non - Recycling control. - Upon a loss of flame the controller will try to restart the burner for the length of timing on the safety switch

Recycling control - the controller will shut down the burner immediately on loss of flame and will attempt to restart the burner once before the control will lock out on safety.

Thermal Sensing Systems --

While neither any oil burner manufacturer or equipment manufacturer has shipped a thermal sensing (one or two piece) oil burner primary with a piece of equipment since 1962/1963 there are several hundred thousand furnaces or boilers in operation today using these older style controllers for burner operation - witness the fact that Honeywell still provides NEW (not rebuilt) for replacement purposes.

These primary controls are usually mounted in the elbow of the “stack” (whether one or two piece controller). The tube containing the sensing element - ( thermal sensor - usually a " U " shaped bi-metal -) is mounted ahead of the barometric control and positioned so that the sensor is located in the path of the hottest flue gases usually the outer radius of the stack .The sensing element should not be exposed to temperatures hotter than 1000 degrees " F " . The element can be permanently distorted. Furthermore, periodic service should include cleaning the “bi-metal. It should be dirt and soot free for proper temperature sensing. Coating the sensor will slow ( inhibit ) the sensor from responding ( expanding longitudinally ) to a temperature rise or fall in the flue gas .On an increase in stack temperature the bi- metal straightens and moves the drive shaft towards the cover end of the control. This outward movement of the drive shaft causes the " clutch fingers " to open and close the " hot and cold " contacts .The clutch fingers ride on the drive shaft and they must be able to freely slide on the drive shaft, however, there must be enough friction between the drive shaft and the clutch fingers so that the drive shaft can cause the " hot and cold " contacts to open and close in the proper operating sequence.

Honeywell's RA116, RA816 and C550 have only one set of contacts and they act as both the hot and cold contacts. Their RA 117 and RA 817 have two sets of contacts.

Stack Relay Operation - RA 116 and RA 816 style controls

When the stack ( flue pipe ) is cold the detector contacts should be in the closed ( made ) position, and the contacts should be open when the stack is hot .When you have a call for heat the thermostat makes a circuit between the 2 "T " terminals on the primary which will pull-in the load relay ( labeled 1 K on diagrams ). The circuit that pulls - in the load relay includes the temperature controller ( usually a room thermostat ) the safety switch contacts , the built - in transformer, the detectors contacts and the safety switch heater. Before the system can begin a call for heat, the “cold contacts “must be in the closed position which indicates “no flame present " and the safety switch must be made .

When relay 1 K is energized, both the ignition transformer and burner motor are powered through contact 1K1. Simultaneously through contact 1K2 a circuit provides separate path for current to by-pass the safety switch and detector contacts. We call this circuit the “hold - in circuit '. At this point there are two circuits operating.

One circuit has a portion of the transformer powering, through the 1K2 and detector contacts the safety switch heater. The second circuit uses another portion of the transformer energizes the thermostat , relay 1K ,safety switch contacts and relay contacts 1K2.With these 2 circuits in play when the detector senses that heat is being produced the detector contacts opens the safety switch heater circuit. The burner, under normal conditions, will continue to function until the thermostat is satisfied. Should the burner fail to light the circuit will continue to heat the safety switch heater and after +/- 70 seconds will open its safety switch contacts , shutting down the burner " on safety " .The burner , to be restarted , must have the safety switch reset manually .In case of flame failure while in the "running mode " the detector ( bi-metal ) will cool and it's contacts will close energizing the safety switch heater and after approximately 70 seconds it will lock out on safety which will require again manual reset.

Stack Relay Operation - RA 117 and RA817 style controls

Physically, then you can easily distinguish between the Intermittent and Interrupted type stack relays - when you remove the covers from each style, the intermittent type has one switching relay and the interrupted style uses two relays in its circuitry. In both the RA 117 and the RA 817 the 1K relay powers the ignition transformer and the 2K relay operates the burner. With this circuitry you can shut down the ignition after the flame has been proven. The cold contacts are closed when the burner is shut down and the hot contacts are closed when the stack is hot.

Again , when we have a call for heat from the thermostat , a circuit is made between the two " T " contacts ( also labeled - W and B ) ,relay 1K ,the safety switch contacts ,the transformer , safety switch heater and the cold contacts . When the relay 1K is energized the ignition transformer is powered through contact 1K1. Physically the transformer is wired to the # 4 terminal on the RA 117/817. The second relay in the RA 117/817 is powered from the “on board transformer “, through the safety switch contacts, contact 1K2 and the thermostat. Relay contact 2K1 powers the burner motor which is wired to terminal #3 (along with the oil valve - if any).The safety switch HEATER will stay energized while the cold contacts remain closed. This circuit uses part of the transformer, the cold contacts, 2K2 and 1K3.

When the left side of the cold contacts opens the safety switch heater will stop to heat. When the right side of the cold contacts open, the ignition will be de-energized because relay 1K has dropped out. Simultaneously, the hot contacts must be closed in order to keep relay 2K energized. This " hold - in " circuit contains the thermostat, safety switch contacts, the hot contacts, part of the transformer and 2K2

On a call for heat , should the burner fail to light , the cold contacts will remain in the closed position , the safety switch heater will continue to heat the safety switch until after the timing of the safety switch causes the switch to open . It must be manually reset. Should flame failure occur during a call for heat the stack will drop in temperature which will cause the detectors hot contacts to open and relay 2K will drop-out which will shut down the burner? In approximately 2 minutes the cold contacts will close and energize the safety switch heater if there is still a call for heat from the thermostat, both the ignition and burner will be re-energized. You will have 70 seconds to re-establish a flame- if you don't the unit will drop -out on safety and must be manually reset.

Next Month in “Sales Bytes "-- All about Optical Sensor Oil Burner Primaries

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net

Questions from the field - August 2006 edition

OIL BURNER FLAME SENSING SAFETY SYSTEMS

Last month's article dealt with older style, thermal sensing technology used in oil burner flame safety systems. This month we will discuss the two piece oil burner flame sensing safety systems, with the focus on the sensor.

Current technology allows us to use detectors that are faster to respond to the combustion process through the use of solid state electronic components, rather than the bi-metal type censors that have been used, and continue to be used so successfully today. Next month we will cover the relay / safety switch portion of this two piece system.

Two piece oil burner systems first were introduced to OEM's in 1960 - these initial systems still used sensing devices that relied upon changes in temperature to operate the oil burner. Remotely mounted relays continued to be used to switch the load of the ignition transformer, burner motor and safety switch. Generally, these relays were mounted on oil burner housing. An evolution of types of sensors occurred with Honeywell and General Controls (then the Ray Brothers - later to become General Controls) leading the industry. General brought to market a thermal sensor that mounted on the fuel line, just behind the oil nozzle. It was wired to the remotely mounted relay with a 3 wire lead . Honeywell countered with 3 different sensors (all thermally activated) and the manufacturer could choose the type that best suited his requirements - each was wired to the relay with a 2 wire cable. Many of the systems that used the Honeywell stack mounted, remote sensors (C550), are still in service today and replacement C550's are still available. The other sensors Honeywell supplied were the C552 - a thermal sensor that mounted in the burner tube, and the C551 - a thermal sensor that utilized a thin sensing rod that was inserted into the combustion chamber. For several years, the relay portions of the systems were modified, but the sensors remained virtually unchanged.

Current Systems

In 1964, Honeywell introduced an oil flame detector, for residential size burners, that uses solid state technology. This new detector consists of a photocell, cell holder, mounting bracket and a 2 wire wiring harness. The photo cell responds to light, not temperature as did the previous sensors. The sensitivity to light is provided through the use of a chemical called Cadmium Sulfide.

The Cadmium Sulfide's (CS) electrical resistance changes as light intensity changes (and almost instantaneously) When there is no light present on the face of the cell , the electrical resistance through the CS is extremely high , on the magnitude of over 400,000 Ohms and at that, point serves as an electrical insulator. When light intensity increases, the electrical resistance decreases. When there is sufficient light present the CS will allow current to flow. This ability will allow an electrical circuit to be completed through the CS when a flame is detected in the oil burner/combustion chamber. As light intensity increases, just slightly, the resistance decreases, however, the amount of light reaching the cell must reduce the cells resistance to its normal operating - which is normally less than 300 Ohms to !000 Ohms in normally adjusted burners -in burners that are in need of service , CS cell resistance can go well over the maximum of 1600 Ohms . At this point, the 1600 Ohms (or above) will cause the relay to trip out on safety. If, when you measure the resistance with an Ohm meter and high resistance is present , you will want to check for a dirty lens on the cell , the cell may have lost its vacuum or the burner may need adjusted (air ratio, oil pressure etc.). These CS cells will respond to any light in the visible spectrum, including artificial light, from such things as flashlights, electric lights and daylight .Most of the light from gas burners is not in the visible range and therefore, they are used, only very infrequently in gas burning equipment. When CS cells are used on gas burners, the cell needs to be applied so that it sees a fuel rich portion of the flame where complete combustion has yet to occur.

Cad Cell Construction

Close examination of a cad cell (White Rogers also uses CS cells with some of their systems) reveals it is made of a ceramic disc that is coated with cadmium sulfide over which a conductive grid is placed. Two electrodes are attached to the ceramic disc which will carry an electrical signal to the primary relay. When the cell is manufactured, it is enclosed in a glass- to-metal seal from which the air is evacuated. This prevents the CS from deteriorating.

Cad Cell Mounting

Most oil burners that use CS detectors have the cell mounted directly behind the static disc, so that it may view the flame through an opening in that disc. This positioning allows the cell to be protected from the oil spray and products of combustion. In addition the cell face should not be exposed to high ambient temperatures - short term 140 F or 120 F normal operating situations. Some burners have the detector mounted in the rear of the burner, above the combustion blower wheel. In any event, the normal operating range for CS resistance should be 1000 Ohms or less. The cells resistance wills, under normal conditions, increase gradually as dirt, soot and oil/grease accumulate under standard operating conditions. You should never have any reason to change the original mounting location. This is the factory approved location and was accepted for proper operation from that location .The cell may be removed from the receptacle for cleaning. Honeywell CS cells can be replaced, if needed, - however, do not replace a White- Rogers cell with a Honeywell cell or vice versa. You need not purchase a C554 (replacement cell, socket, bracket and wiring harness) for service - just purchase for Honeywell replacements the # 120367.

Next Month

We will review the different relays that work with Honeywell CS cells Watch for these topics in future issues - Hydronic Zone Valves - Switching Relays and Hydronic Relays.

Do you want some information on a particular controls problem?
Bill can be reached at 281-537-2701 or threesons@ev1.net
 

Oil Burner Safety Switch Circuits - September 2006
Part 2 of 3

In previous issues of “Sales Bytes" we discussed the operating sequences of both Thermal Sensitive oil burner primaries and Optical flame oil burner flame sensing systems (Cad Cell Primaries). This month we will review some of the details about the different types of safety switches used by Honeywell in their oil burner primaries .The evolution of these switches has been nothing short of amazing (but seemingly agonizingly slow). I suggest that if you are deeply involved with oil burner primaries that you would be well advised to contact Honeywell's web site for specific copies of the specification sheets in which you are in need of information - there is no charge - they are extremely detailed in every facet of the devices' installation, servicing and troubleshooting . You may contact Honeywell @ http://customer.honeywell.com or by telephone to their technical “Hot Line “@ 1-800-468-1502. Please be specific about the device in which you are interested.

The purpose of the " Safety switch " is to shut the burner down in case of a malfunction in the burners operation There have been approximately 4 different types of safety switches ( plus many iterations ) which have been used since the advent of the "Stack Switch".

The first Stack Relays used an open type of switch concealed under the cover - an electrical / mechanical type switch that, as the bi-metal heated during a burner malfunction, would warp the bi-metal switch open - thus shutting down the burners operation.

Since the safety switch was exposed when the primary’s cover was removed the stories are legend about clever homeowners use of rubber bands , matchbook covers , dental floss and various other materials to by-pass the safety switches' purpose - No need to cover them in detail here - hopefully most of these stack relays are out of service now , or at least they should have been replaced by this time .These models would include the R116 and R117 - ( Not the more current RA116 and RA117 units ). Most stack relays used safety switch timings of approximately 70 seconds .

Cad Cell Primaries - (1961---) two principle types of safety switches have been applied to these systems and they are easily identified. On the earliest versions (R8118, R8169 and similar line voltage primaries) an electro - mechanical design was incorporated into these type devices to respond to a loss of flame in the burner system and to stop the burner from continuing to operate. Electronics allowed Honeywell to introduce, in the "Cad Cell " primaries, a much closer control of safety switch timings because ambient temperatures and wide swings in voltage could more easily be handled...

Honeywell, with the introduction of these new cad cell primaries, was now able to offer to OEM's a choice of safety switch timings - 15, 30, or 45 seconds. The OEM chose the timing which matched the capacity of his burner - up to 4 GPH. MOST RESIDENTIAL BURNERS USE THE 45 SECOND TIMING, WHICH IS THE VERSION CARRIED ON DISTRIBUTOR'S SHELVES FOR REPLACEMENT WORK. THE ADMONITION IS, NEVER USE A SAFETY SWITCH TIMING LONGER THAN ON THE RELAY SUPPLIED BY THE BURNER MANUFACTURER. The problem is obvious and does not need further discussion.

In each event, when the relay “locks out ", the safety switch reset button must be manually be reset. The burner will remain disabled until the red reset button is pushed. The resetting of the reset button will allow the burner to restart as long as there continues to be a call for heat.

The earliest cad cell relays made by Honeywell utilized a relay called a "sensitive relay" which was incorporated into the safety switch circuit. The relay used two bi-furcated contacts (DPDT) in the safety switch circuit to be able to switch the extremely small currents that are carried through the cadmium supplied cell. These contacts were described as “whisker” contacts and their very small surface area prevented an accumulation of dust occurring which could cause nuisance shutdowns. These relays were easily identified through these clear plastic cover around the relay. No replacement or service is possible on this relay If the unit has failed you must replace the entire relay. Later versions of the cad cell oil burner primary(R 8184 G etc...)Use a solid state equivalent for the safety switch circuit .The Triac, bi-lateral switch, 2 resistors and 2 capacitors make up the components that replace the older electro-mechanical version of the safety switch circuit.

The solid state flame sensing circuit is designed so that the Triac will conduct current only when the resistance is high (indicating a lack of an adequate burner flame). When the cad cell resistance is high , the voltage across the bi-lateral switch exceeds the break over voltage which causes it conduct current and thus triggers the Triac . The capacitors purpose is to supply pulse of current on every 1/2 Hertz in order to assure that the break over voltage is exceeded .When the Triac is in the conducting mode (when the cad cells' resistance is high) when you have a call for heat from the system's thermostat the # 1 K relay (Shown in the Honeywell diagrams) gets energized. When Relay # 1K is energized it will close its contacts # 1K1 and 1K2 and the burners ' components (Burner motor, oil valve and ignition transformer) are energized .When the flame is established, the cad cells' resistance will reduce, the voltage across the bi-lateral switch falls below the break over voltage point which causes the Triac to stop. Then the Triac switch stops conducting, which causes the safety switch to drop out of the circuit allowing the oil burner to continue to run. The # 1k relay stays powered through its # 1K1 contact and will continue UN till a loss of flame or the thermostat is satisfied.

On flame failure, the cad cells' resistance increases until the Triac is energized. At this point the safety switch heater continues to heat till the bi-metal warps enough to break the its circuit which then causes the burner to shut down. The red reset button must be manually pressed for the burner to be able to restart.

Next month we’ll take a look at today’s current models of cad cell primary controls.

Oil Burner Safety Switch Circuits - October 2006
Part 3 of 3

In previous issues of “Sales Bytes" we discussed the operating sequences of both Thermal Sensitive oil burner primaries and Optical flame oil burner flame sensing systems (Cad Cell Primaries). This month we will review some of the details about the different types of safety switches used by Honeywell in their oil burner primaries .The evolution of these switches has been nothing short of amazing (but seemingly agonizingly slow). I suggest that if you are involved with oil burner primaries that you would be well advised to contact Honeywell's web site for specific copies of the specification sheets in which you are in need of information - there is no charge - they are extremely detailed in every facet of the devices' installation, servicing and troubleshooting . You may contact Honeywell @ http://customer.honeywell.com or by telephone to their technical “Hot Line “@ 1-800-468-1502. Please be specific about the device in which you are interested.

Current Cad Cell Primaries --- (R 7184 Family)
In recently introduced cad cell primaries, the miniaturization of electronic components has allowed Honeywell to incorporate a number of new features which enhance the controls' versatility and desirability to the manufacturer, service technician and homeowner. This new family of cad cell oil burner relays use a status LED and a new type reset button which, when used together, will provide an indication of the following :

# 1. - Presence of burner flame
# 2. - Relative flame level (Cad Cell Ohm Resistance)
# 3. - The control is in lockout.
# 4. - The control is in re-cycle.

This multi-function light is used together with a new style reset button to provide the service technician with information about the burner’s operation. These devices provide more precise control under a much more variable range of voltages and ambient temperatures than older style devices .The addition of various timing functions also provides a wider range of application flexibility for OEM's These include :

# 1. - Fuel oil valve on-timing -- 0 or 15 seconds.
# 2. - Burner - off delay timing 0, 2, 4, 6 minutes
# 3. - Lockout timing - 15, 30, 45 seconds
# 4. - Ignition carryover - 10 seconds
# 5. - Recycle delay - 60 seconds

If you have any questions that these articles haven’t answered please feel free to contact me at threesons1@peoplepc.com.
 

Residential Hydronic Zone Valves - December 2006
Facts About Application, Selection, Sizing and Servicing

• Capacity Index (Cv) defines just how much water can pass through a valve at a specific pressure drop (PSI). The OEM's spec sheets provide graphs of these capacities.

Example : A valve with a Cv rating of 7 means that with a pressure drop of 1 PSI across the valve that the valve can handle 7 gallons of water per minute (GPM). A valve rated at 2 Cv will carry 2 GPM with a pressure drop of 1 pound across the valve. Cv ratings are universally used throughout the industry.

• Changing the inlet and / or the outlet size of the valve does not necessarily alter the valves capacity (flow rate). The valves internal porting governs the flow rate.

Example: Honeywell's V8043A1003 1/2" x 1/2' valve has the same capacity as their V8043A1029 3/4x 3/4”. The valves capacity is 3.5 gallons per minute with a 1 pound drop across the valve. With different pressure drops across the valve, the capacity changes. For example, with a pressure drop of 5 PSI, the valves capacity ( V8043A1003 ) becomes 8 GPM. The same valve, with a pressure drop across the valve of 1/2 PSI, the capacity changes to 2 ½ GPM. For most residential systems a valve with a 3.5 Cv rating will suffice for the average zone. This would provide approximately 35,000 BTU's at normal operating temperatures .Valves are available in 1, 2.5, 3.5, 4, 7 and 8 Cv ratings.

• Certain manufacturers have different valves for different media, i.e... One valve for hot water, another for cold water and still a different valve for steam systems. Honeywell is a typical in providing this choice.

• If you are providing or servicing a low voltage zone valve system, I would caution you in selecting the step-down transformer you supply to power the system’s components. In order to determine the proper size transformer ( Va rating ) that should be used - multiply the valve's power need (coil draw of the valve motor, i.e.. .32 amps AC .etc . ) x 24 volts AC . That provides the amount of energy needed to power 1 zone valve.

Example - .768 Volts x amps. Multiply the number of zone valves to be used in the system for the total VA required (for the zone valves only). If you will have 8 valves in the system, you will require 61 + VA In this example the best (least expensive route) would be 240 VA transformers or a 40 and 30. A 49 VA and a 20 VA won't hack it. Prepare for the worst case scenario: Don't overload the transformer's total output - When power failure occurs, all valves will try to open simultaneously - the valve motors inrush needs will cause the transformer to fail.

• Many valves have manual openers (some are at extra cost). When used during a power failure, these openers will return to the normally closed position, ready for the next power failure. Be certain to brief the home owner on this feature. This won't provide a lot of comfort, but it probably will keep some degree of livability in the home through the effects of gravity.

• Most complaints of “water hammer” are a result of valves being installed in the piping backwards - yes, backwards.

• Using a valve with an "end switch" (optional feature on some brand valves) will allow you to power a circulating pump (up to 4.4 amps @ 120 Volts) without using a relay. Take care to check pump's current draw.

• Honeywell valves (V8043 type) should be used only in systems that do not contain Dissolved Oxygen. Most frequently systems that use constant resupply of make-up water will contain “Dissolved Oxygen”.
 

Mr. Control Pro Most Frequent Questions for 2006 January 2007 issue

In this months' issue of " Sales Bytes " I'll try to catch up with a number of questions I've received from a number of people about the same ( or similar ) subjects.

1. 24 VAC pilot igniter on Honeywell’s “Smart Valve " system.
• The normal warm-up timing for the 24 VAC igniter is 2 +/- seconds. This timing will lengthen - slightly - as the igniter ages.
• The warm-up timing for the 120 V ac igniters varies - depending on the model - either 17 seconds or 34 seconds. Some new models, used with advanced versions of the “Smart Valve “systems can have warmed - up timings as short as 5 seconds.
• The line voltage igniters (normally Norton is the largest supplier of these items) are made of Silicone Carbide alloys and this material has a very high initial resistance to current flow - thus the long warm-up timings.
• The 24 VAC igniter is constructed from an alloy of Silicone Nitride, is much less brittle than Silicone Carbide and has a very low initial resistance to current flow. Therefore it reaches the proper temperature for gas ignition very quickly .

2. New gun-tube type oil burners will normally provide a very low initial Ohm reading from the Cadmium cell on start up (generally in the range of 100 to 200 Ohm’s. As the burner fires, through time, the blast tube will accumulate oil and soot, thereby providing a condition for adsorption of light which is needed for flame detection on the “Cad Cells " face. This reduction of cell light causes an increase in Ohms resistance in the Cad cell. When this resistance reaches a level of over > 1000 Ohms the cell will need cleaning or even replacing. The oil burner primary responds to differing signals from the “Cad cell " to either permit the burner to operate or shut down on “safety "

3. The load switching ratings for relays and for contactors are those ratings based upon those certified when they are tested in the vertical mounting poison. Those ratings will normally decrease when the relay or contactor is mounted horizontally. This really applies only to non-electronically constituted devices. “The older stuff - open contacts etc... - "

4. “Smart Valve” igniters should measure about 3.7 + /- Ohms when new, cold -not powered. As the igniter ages its' resistance will increase. When its cold, measured resistance increases to 10 Ohms it must be replaced. Constant, reliable operation depends on the quality of the igniter. Hot spots on the igniter signal the need for replacement.

5. When the manual opener is used on Honeywell's V8043 family of hydronic zone valves ( because of a loss of power ) the valve will automatically cycle to the closed - normal operating position when power is restored. You achieve only about 60% of full flow in manual operating position.

6. Honeywell builds V8043 zone valves specifically for steam service. Don't attempt to use their regular V8043's on steam. The revolving valve ball will not survive steam temperatures.

7. The Honeywell V8044 water service valves are DIVERTING VALVES AND ARE NOT INTENDED FOR USE AS MIXING VALVES.

Hopefully these comments will answer some of the things that have raised questions for either yourselves or your technicians.

Thermocouples and Self Generators February 2007 issue

While I haven't directly addressed the issue of Thermocouples and / or Self-Generating "D. C.” power supplies, I continue to receive questions about these devices. That tells me there must be some misconception and misunderstanding about these devices which makes this topic quite timely. I'll cover single thermocouples Operating Principles this month and continue next month with Operating Standards by code bodies.

The fundamental operating principles of thermocouples have been used in the HVAC industry since about the 1910's. Through the years these devices have been used in both heating AND cooling systems (Gas Fired A/C units). Not counting the millions of gas fired water heaters, it is estimated that there are over 40 million gas fired heating appliances in service today. Furnaces, boilers, unit heaters, spas, duct heaters, wall heaters and floor furnaces, just to name a few. So we need a fundamental understanding about these units. How they operate, how they are tested and serviced.

OPERATING PRINCIPLES

Two dissimilar metals are bonded together at one end (usually stainless steel and Copel - a copper/nickel alloy - for the temperatures seen in heating / cooling systems). Other applications for this technology, i.e., industrial temperature reading etc., utilize other types of metals joined together - but they each operate exactly the same way. When the welded junction of the two metals is heated (called the hot junction) the heat applied will create an energy flow. For or our purposes we will work with current in the magnitude of +/- 30 millivolts dc. This amount of current will be sufficient to energize the coil of the pilot gas valve and will normally hold the valve seat in the open position. Important: the energy created by heating the hot junction of the thermocouple is not sufficient, in and of itself, to pull the valve seat up (open). First, you must turn the pilot gas cock knob to the pilot gas flow position and depress the knob - this action will force open the pilot gas valve seat ,sealing it against the pole pieces of the "horseshoe" shaped magnet. The magnet is not strong enough to "Pull-in" the valve disc - just strong enough to "Hold it in". Having held the gas cock in the depressed mode for + / - one minute, manually igniting the pilot gas, the current generated by a properly sized and adjusted pilot, heating a properly located and shielded thermocouple should hold the pilot gas valve open. Once the pilot valve is held in the open position, by the current generated by the thermocouple, you must then release the pilot gas cock - the pilot gas should continue to burn and you must turn the gas cock to the "on" position. With a call for heat, the main valve should open and the main burner should safely light off. On a loss of the pilot gas flame, (for whatever reason - drafts, gas pressure issues, clogged pilot orifices etc...) the thermocouple tip will cool below the temperature required to heat it sufficiently to generate enough current to hold the pilot gas valve open, and should this event occur, the main fuel valve will be starved of gas -even though the main valve could remain open due to a continuing call for heat from the controller (usually a thermostat) Thus, the burner would safely shut down. The safety built into the operating system of the appliance depends upon a correctly functioning thermocouple / pilot burner combination.

Next month: Operating Standards
 

Thermocouples and Self Generators March 2007 issue

# 1. - Standards for gas burning appliances are written by "ANSI" - the American National Standards Institute. The appliances are tested for compliance to these standards by approval bodies, of which there are several - A.G.A. (America can Gas Association) being the most widely recognized. These bodies DO NOT write the standards to which they test.

The standard fitting for thermocouples operation is the standard that says, "The safety shut down system must recognize the lack of pilot flame (flame failure) for gas burning appliances, of less than 400,000 BTUH capacity, in 180 seconds or less and shut the system down.” THAT'S 3 MINUTES. Most thermocouples will cool down sufficiently, to shut the system down, in about 60 seconds - but 180 seconds will meet code requirements. Modern “Flame rectification” systems react in + / - 2 seconds - a whopping difference. However, thermocouple operated appliances are still a very safe operating system indeed.

# 2. - With no load connected to the coil, a new thermocouple will usually be capable of producing an output of +/- 30 millivolts. This output is based on a tip temperature of approximately 780 -800 degrees F. As you increase the tip temperature the millivoltage output will increase and when heating the tip with propane torch you could easily find an output of over 40 millivolts. However the cooler you are able to run the tip temperatures (less than 1000 degrees F is optimum) the longer life expectancy for the ‘couple. Many manufacturers will not warranty their thermocouples - Honeywell warrants all of their equipment- including 'couples. They have two quality thermocouple devices available - the Q340 - rated as a 10 year life average and the Q390 which is a 5 year device.

In order to create the current flow required a temperature differential must be achieved - the greater the dif-Terence between the hot junction and the cold junction -the greater the millivolts output. The maximum temperature on the cold junction allowable is 780 F. Maximum hot junction is 1400 F The ideal temperature on the hot junction is 780 -800 degrees F. This, for example, should be the range you would reach with a pilot, such as Honeywell’s Q314 using a .018 natural gas orifice and pilot gas with a pressure of 3.5 "o.k.”. These factors should produce an optimum operating situation for a thermocouple.

The Q340, 24 inch length, has a resistance of 0.02 Ohms, its lowest acceptable open circuit output is 18 millivolts and under. Turndown, open circuit is minimum 2 millivolts. If you require further explanation of this data, feel free to call me. The lowest permissible open circuit rating is based upon the lowest acceptable turndown rating of 18 millivolts.

I'll continue this discussion of “Thermocouples, Thermopiles and Pilots in next month’s issue.

When is a Contactor Not a Relay? June 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com 

It’s cooling season, and you’ll be replacing contactors and relays every day. Aren’t all contactors and relays pretty much the same? Nope. As you might expect, there are many differences. This month I’ll write about the basic characteristics of contactors, and next month will be the same on relays.

U. L. says anything over 20 amps full load (AFL) or more is a contactor. They are three types:

1. General Purpose contactors
2. Definite Purpose contactors
3. Motor Starters

All these switching devices share many features in common. Each on has one or more sets of contacts that will open or close a controlled circuit. Each is activated by a separate controlling circuit. For example, a 24 VAC control circuit through a thermostat might connect power to a 120 VAC blower motor.

Most contactors use a magnetic coil in the control circuit that, when energized, will pull in the load bearing contacts. The load contacts are generally made of silver cadmium oxide and the amount of silver in the contacts and the method used to bond the contacts helps to define the maximum load the contacts can carry.

Any contactor may have 1-4 sets of switching contacts, known as “poles”. These poles may be in the normally open (NO) position when there is no power to the controlling circuit, or they may be normally closed (NC) when there is no power to the controlling circuit.

General Purpose Contactors

As the name implies these contactors can be used in a wide variety of applications. They are generally build for a longer life and can stand repeated changes of replacement control circuit coils.

Definite Purpose Contactors

These devices are used in residential and light commercial AC systems, heat pumps and electric furnaces. Each contact is built to handle a specific load, i.e., 25 Amps. There is an addition rating called “locked rotor” which is the starting current required to get the motor off of its stopped condition into a running condition. The locked rotor rating may be as much as 6 times the running amp rating. Today’s motors are more efficient than those in the past and so the locked rotor rating is of less importance than it has been. Beware of replacing contactors on old equipment...the older the load device the higher the starting amp requirement you will have.

Motor Starters

Motor starters are contactors that are designed to switch heavy motor loads and may include additional features such as overload protection, holding contacts, step resistors, disconnects, and more. Older style compressors and some fan motors are usually controlled through motor starters.

Relays: Everything You Need To Know July 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

Last month’s discussion centered on contactors. These devices are used in our industry to switch larger electrical loads in excess of 20 amps. Generally these loads are AC compressors and air handler motors. This month our focus will be relays. Relays allow us to remotely control many types of circuits and loads and also provide the ability to control larger loads with very sensitive controller-devices that would not be able to switch these loads by themselves.

The advent of solid state components and micro-processors makes it virtually impossible to describe here the variety of types of switching configurations and mounting methods to be found. Many relays are mounted on circuit boards and they are not designed to be replaced in the field - if the relay fails the entire device must be replaced - such as those used on Integrated Furnace Controls and Electronic Fan Timers. A high percentage of hydronic heating systems, for example, use remotely mounted relays for control of the circulating pump(s) and these systems typically utilize switching relays encased in cases and covers. Many case and cover relays may be replaced on the job. For example, RBM and Honeywell have manufactured, for years, field replaceable, plug-in style relays, which are mounted on circuit board receptors (held in place by "bails ").

Relays are called, frequently; by the name of the circuit function they are to provide- Thermal Delay Relay, Time Delay Relay, Impedance Relay, Sequencing Relay etc...

A description of the function provided by the Impedance relay is as follows. An impedance relay permits (in a residential type A/C sytem) compressor lockout and provides remote reset for the consumer. This eliminates the necessity for a manual reset overload control or pressure sensor. The relay has a low voltage pull-in coil and contains two sets of contacts-one single pole/single throw- normally open (SPSTNO) set of switching contacts and one single pole/single throw - normally closed (SPSTNC) set of contacts. During normal operating conditions, the normally closed set of contacts in the pressure switch and the compressor motor overload short out the impedance relay coil. The contactor coil is wired in series with the coil of the impedance relay . The contactor coil is also wired in series with the SPSTNC relay contact and the overload and/or pressure cutout contacts which are both normally closed. When the thermostat calls for cooling, the compressor contactor is powered through the contactor's coil, and the impedance relay's SPSTNC contacts (which are wired in parallel with the impedance relay coil) and the pressure switch and/or overload contacts.The high impedance of the impedance relay coil prevents the impedance relay from pulling-in during normal operation. Should either the pressure switch or overloads open, the impedance relay coil is then placed in series with the contactor coil. Most of the voltage in this circuit is used by the impedance relay coil and as a result the compressor contactor drops out. When the impedance relay pulls in, its normally closed set of closed contacts (SPSTNC) opens which holds the compressor off line. While this system has lost favor over the past few years many,many systems that use this circuit are still in service today. To reset the circuit -simply satisfy the thermostat and the impedance relay will drop-out. This is easily accomplished by moving the thermostat's system selector switch to the "off" position.

Relays that contain electro- mechanical contacts are designed to be mounted with the mounting base in the vertical position (same applies to most contactors). Gravity plays a role in the contact ratings and for maximum switching service - vertical is the key word.

Another example of a relay designed with a specific purpose in mind is the Electric Heat relay. Again these types of relays are available in a wide variety of shapes, sizes and switching configurations- with and without cases and covers for panel and individual mounting. Some include step-down transformers in order to provide low volt circuit power for thermostat control.

Sequencers designed to switch electric heat loads (baseboard resistance elements as well as strips in central furnace systems) are designed to carry maximum specific loads These ratings are specified in Full Load amps, and Resistive Loads.Many also will show their rating for Locked Rotor amps.

A typical electric heat relay is listed at U.L. with the following load switching characteristics:

Full Load              Resistive         Locked Rotor
2.8A @ 600Vac      10A @ 600Vac      14A @ 600Vac
3.5A @ 480Vac    12.5A @ 480Vac   17.5A @ 480Vac
7.0A @ 120Vac      25A @ 120Vac      35A @ 120Vac
208 ,240 &          208,240 &         208,240 &
277Vac             277Vac           277Vac

It would, as you can understand, be nearly impossible to detail all of the various types of relays available in the market place in the space and time allotted here-manufacturers, however, generally speaking, are quite helpful with their catalog listings. Be carefull to select a relay that is rated to swich the load or circuit with which you are dealing . Don't try to swich a Powerpile load with a switch that is not specifically rated to switch “Pilot Duty" loads. The types of devices that will satisfactorily switch Powerpile loads normally include gold flashed contacts ( very low resistance to current flow). Should you, by mistake, try to switch a heavier load than Powerpile on these contacts the gold flashing will be "blown away" and the contact will no longer be suitable for "Pilot Duty" service

See you next month with the answers to some frequently asked questions.
 

Transformer, Thermocouple and Relay Tech Tips August 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

This month I’ll answer three of the questions I received by email in the past month:

1. What are NEMA transformers?
2. What does “open circuit” on a thermocouple mean?
3. What does “pilot duty” relay mean?


NEMA Transformers

Several have asked about "NEMA" transformers. Why it is important to use them and what's difference between a "regular" transformer and a NEMA transformer?

NEMA (National Electrical Manufacturers Association) has developed very precise criteria by which the performance of low voltage (< 30 Volts A/C) transformers is judged. It is critical, especially with the electronic components and circuitry used in HVAC equipment currently produced, that the equipment's system transformer produce predictably, repeatedly and reliably voltages within a certain output range. System performance depends upon this accurate output. The standards, to which a transformer must perform, to be rated as a "NEMA" rated device: NEMA Standard 20-92

With 0 % load connected to the secondary, 26 1/2 Vac-is normal, with a range allowable of +/- 1/2 Vac output. (26 to 27 Vac is the standard.)

With 100% load (i.e... a 40 VA load on a transformer rated for 40 VA max capacity) the secondary voltage output must be 24 Vac- +/- 1Vac. (23 to 25 Vac is the allowable output range)

With 200% load (i.e... an 80 VA load on a transformer rated for 40 VA max capacity) secondary voltage output of 21 1/2 Vac +/- 1 1/2 Vac (20 to 23 Vac is the acceptable output range.).


Many equipment manufacturers are specifying that the transformers they utilize on their equipment must be NEMA rated and warranties are voided if transformers used in servicing this equipment are used.

Many different problems have been created, through the years, by poorly performing transformers. One of the most familiar problems is when there is "over cooling” when using the Honeywell T87/Q539 thermostat /sub-base combination and a substandard transformer. Since the cooling "anticipator” is the only load on the transformer secondary when there is no call for cooling and there is a higher output on the transformer secondary, 28, 29, 30 Vac or even higher, the 3000 ohm (+/- 5%) thermostat cooling anticipator will overheat causing the stat to call for cooling more quickly than needed and will remain calling for cooling on longer than needed resulting in "over cooling" the space. Wide temperature swings then cause familiar consumer complaints. Replace the transformer and fix the problem!

Thermocouple Open Circuit Question

Your article about "Thermocouples" mentioned the "open circuit” range of millivoltage outputs for "normal" single thermocouples - what should the minimum output be with the pilot safety coil under power?

If you are measuring the "closed circuit" output of a thermocouple (each different thermocouple will have its own output curve) the test should be run with the thermocouple operating in its own pilot burner, with normal gas pressure on the pilot. In other words the test should be run with the test conditions the same as the thermocouple would operate under normally. I can tell you that the range of outputs for the Honeywell Q340 varies from a lowest acceptable output of 18 ma (open circuit) with a "turndown minimum output of 2 ma, a normal open circuit output of 26 to 32 ma and an open circuit output with a "closed circuit" output of 7 to 9 ma.

In the case of the Q340 thermocouple and the pilot applied to the unit must be able to satisfactorily light the main burner in 4 seconds or less (with no singeing of a tissue placed over the vestibule opening or "oil canning" of the cabinet) with the pilot / thermocouple combination producing an output of 2 ma. If this test is not passed, the entire piece of equipment under test will not pass and the OEM must go back to the drawing boards until they can satisfactorily pass the test.


What Are Pilot Duty Contacts?

What do you mean by the term "Pilot Duty Contacts" when talking about relays?

The term "Pilot Duty” rated contacts, when used in reference to control devices , such as relays and other pieces of electrical load switching equipment, refers to that specific device’s ability to switch or control very small electrical loads (i.e.0.25 amps @ 0.25 to 12 Vdc or less ) These devices, when designed to switch these very small loads are generally made with gold (or other precious metal ) plated or "flashed" contacts because these precious metals have extremely small resistance to current flow. Normally the plating is quite light or "thin' and should you place a higher voltage (Load) on these specific contacts, the contact will no longer be able to switch this very small electrical load because the plating will have then been " blown" off the contacts and will not operate satisfactorily in a millivoltage type load .


I enjoy hearing from you and trying to respond to your questions. More answers next month.

Setting Heat Anticipators on Electric and Electronic Thermostats
September 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

DEALER QUESTION - We are somewhat confused about the proper way of setting heat anticipators on both electric and electronic thermostats. I guess we don't really understand what they are for. Further, what effect they have on the furnace's cycling rate. Will you help us out?

ANSWER - First -the question about the "heat anticipator purpose. The heat anticipator is an integral and most important component in the thermostat. Without an anticipator, the thermostat would have to rely only on its sensing element (usually a bimetal) to respond to changes in the controlled spaces’ temperature. These "stats" need a boost to be able to more nearly track the room's temperature. The anticipator applies additional heat (produced by the current flow through the anticipator) and as a result the "stats" sensing element responds much more rapidly to room temperature changes. An electro-mechanical thermostat, without an anticipator, is about the same as having an automobile with square tires. The car will get you where you are going but neither very rapidly or smoothly- the same may be said of an anticipator-less thermostat.

There are two types of anticipators used in electro-mechanical thermostats today:

#1 - Fixed (non-adjustable). Thermostats that employ fixed heaters are designed to match the needs of specific "loads". For example- a special model is designed specifically to operate " Powerpile " type gas valves. These thermostats have a fixed (non-adjustable ) heat anticipator and they will not work effectively with any other type of load. Sometimes they are referred to as “Pilot Duty " rated thermostats. In most instances they are able to carry only loads of 750 millivolts or less.

#2 - Adjustable heat anticipators. Adjustable heater thermostats are found on well over 99% of equipment systems in use today. As the name implies - the "heater" is adjustable and may be adjusted to match many different "loads" Negates the need to have a special thermostat for every load. What a nightmare that would be. We describe the "heater" as "wire wound" And it has a scale plate connected - the scale plate is graduated in tenths of one amp. The Honeywell T87 has a scale plate (On the standard model) from 1.2 to .1 amps. The adjustment pointer may be moved to any point along the scale. And should be set on the proper amp draw marking that will create the “Cycle " pattern needed for that particular piece of equipment Later we will cover the "Cycle" rate issue.

#3 - Fixed “Carbon Heaters". The earliest thermostats with heat anticipation are no longer built (such as the Honeywell T11, T147, T19, T109, T111and TM147). They used small carbon, color coded, fixed resistance plug-in style heaters. These heaters were available in about 19/20 resistances. The technician had to pick-out and plug-in the resister that most nearly matched the load he wished to cycle There are still, even today , some of these thermostats in service -should you come across one of them - for your customers sake please replace it.( and put it in your showroom museum of old controls etc,)

Electronic thermostat heater setting will be covered later in this same article

The second part of his question dealt with "cycle rate". The proper "Cycle" rate is determined (through exhaustive laboratory testing and analysis) by the equipment manufacturer and with a very few exceptions will follow the guidelines shown below. You should however, follow the recommendations of the equipment manufacturer when they are available to you. By definition a CPH is one full "ON" and one full "OFF" period on the appliance. Cycle rate settings are based upon the load on the equipment @ 50%. For example : a 6 cycle rate would at 50% load produce a timing of approximately 5 minutes "on" and 5 minutes “off" at design.

#1 - Use 1 (one) Cycle per Hour (CPH) for one and two pipe steam systems

#2 - Use 3 (three) CPH for Conventional hydronic systems. (non-fin tube type radiation)

Condensing style gas furnaces #3 - Use 6 (six) CPH for Conventional style fossil fuel furnaces (Gas and Oil)

Hydronic Systems using zone valves (copper and aluminum fin tube radiation) matching the anticipator to the zone valves current draw.

#4 - Use 9 (nine) CPH for ducted electric resistance furnaces. It is of critical importance that the thermostat heater be set properly in order to achieve the optimum operating efficiency and to provide the maximum comfort possible for the customer.

The details that have dictated these cycle patterns are far too complex to cover in any detail in the space we have available here but, rest assured-these have stood the test of time. Factored in , among many , many considerations are such things as the design of the heat exchanger, its adsorption and desorption rates etc.The technician's ability to install and set-up the thermostat correctly is of paramount importance and only when the correct procedures are followed will the user receive all the benefits for which he has paid.

In order to set the heat anticipator to match the CPH rates shown above- use the following chart. Please, first measure the circuit's current draw at the thermostat- not at the equipment. This amp reading will be the value you must use to determine the proper set point on the scale for the cycle rate you want to use.

#1 - 1 (ONE) CPH Multiply your amp reading X TWO. For example - if you read .45 at the thermostat (system "on” for at least one minute before reading) multiply the .45 by two - or .9. That is the proper place to set the pointer.

#2 - 3 (THREE) CPH Multiply your amp reading X1.4 ( 140%)

#3 - 6 (SIX) CPH Use the amp draw you get at the thermostat for the anticipator set point For example -read .8 Set the pointer at .8

#4 - 9 (NINE) CPH. Multiply your thermostat reading X .7 (70%) Example - you read .54amps. Multiply .54by 70% or .378 set the pointer at about the .38 to .4 spot on the scale.

ELECTRONIC THERMOSTAT CYCLE SETTING

There are many, many different brand electronic thermostats available on the market today. Obviously on have chosen Honeywell for illustration purposes.

When the installer elects to install a Honeywell Vision PRO" he merely needs to wire the terminals that are required to operate the system and mount the "stat". No more does he have to make meter readings to set the anticipator.

Following the specification sheet he needs to enter "The Installer Set-up Mode". When the "Vision Pro's" backlit screen is pressed it will light up a reveal a matrix. He then selects the cycle he wishes to use - press that option and the cycle rate selection is completed. I suggest that the "tech" first read over the instructions so that the many options in this family of thermostats makes them indeed "Universal” in their wide range of applications.
 

Charcoal Filters and Redundant Gas Valves
October 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

Several questions have come in (by phone and e-mail) since last month's edition of "Sales Bytes" and some of them may strike a familiar chord with some of you, as well.

Question # 1.

How much "Ozone" (O/3) will charcoal filters adsorb? We use them in some electronic air cleaner applications and they seem quite effective as many of our frequent "Ozone" complaints have been greatly reduced?

Answer # 1.

Charcoal, which is made from activated carbon , does not really adsorb "Ozone" , but in fact, the " charcoal " acts as a catalyst for two O-3 ( unstable oxygen ) and it re-arranges it's molecular structure to three O-2 , normal oxygen.

"Charcoal" will, however, adsorb other gases ( Cooking, smoking pet odors etc...) but it is not designed to remove particulate matter- although if left unprotected by an effective air filter it will in fact load up with lint, dust ,dirt etc. very quickly and consequently need "cleaning" or replacement fairly quickly. When the activated carbon has loaded to its capacity it will then desorb the sum of the gases it has removed. Sometimes the outgassing is worse than any of the individual odors alone

High pressure drop is a large problem when dealing with "charcoal filters" It's been demonstrated that 1/2 " thick "egg crate" style filter which is coated with activated carbon works best in regular HVAC systems because of it's low Delta-P.


Question # 2.

We have a number of heating units that we service that have non-redundant gas valves and that utilize an additional limit that is generally located in the combustion chamber. We consistently have "call-backs" on these jobs because, I believe, we have replaced either the limit or thermocouple in error. Got any suggestion?

Answer # 2.

A little history, which may help to explain some of the questions you have When ANSI changed the gas train requirements as of Jan. 1st , 1979, they wrote a requirement that said all new equipment must be structured so that they met one of these three dictums.

# 1. The gas train must include a redundant (dual safety shut-off) gas valve -or,
# 2. The gas train must have two (2) single safety shut -off valves, piped in series and wired in parallel -or
# 3. The control string in the system had to have an additional high limit, wired in series, with the rest of the required limits. In addition, this limit had to be a "one - shot" limit. This limit would have to be in addition to any other limit normally required in an appliance of its type.

I mention this requirement because the extra limit, usually similar in design (snap-disc variety) to limits used in electric resistance furnaces, was wired into the thermocouple circuit. When the extra limit would open, it opened the circuit to the safety shut-off coil which in turn closes the main shut - off valve. Thus achieving, to some degree, redundancy.

The critical point to remember is that if AWG 18 wire is used to wire from the limit to the thermocouple circuit a maximum length of 13 inches of wire be used - and the thermocouple has to be a maximum of 18 inches in length. When the wire between the thermocouple and the limit is AWG 16, the length of wire should not exceed 22 inches and the thermocouple should not be longer than 18 inches in length. Should the connecting wire from the limit to the thermocouple be AWG 14, the wire length can be 35 inches and the thermocouple 18 inches long.

Various models of thermocouples will have slightly different wire length requirements (mostly more limiting). I have quoted the data for Honeywell's Q 340 thermocouple series. The important point to remember is ”Never use a longer replacement thermocouple than the original thermocouple used in the equipment”. The added resistance can and will cause nuisance problems.

Question # 3.

With electric thermostats (mercury switch type) where is the best place to take amp draw readings in order to set the heater correctly? Most of the men I work with tell me to take the readings at the valve- it will save a trip up the stairs. What do you recommend?

Answer # 3.

Phillip, I ALWAYS advise, when asked, that these readings be made at the thermostat -across the R and W terminals (stat off of the sub-base or wall plate). Let the circuit be completed through the meter and after allowing the unit to operate for about a minute take your reading. This will assure you that the entire load that affects the cycling rate of your system will be accounted for and you can correctly set the “heat anticipator. I have previously discussed the proper method of setting anticipators in previous issues of “Sales Bytes”


These sums up some of the questions this month- keep them coming. I enjoy hearing from you.

Getting Your Hands On a Hot Surface Igniter…Does It Matter?
November 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

Tell me about the physical handling of Hot Surface Igniters (HSI). Will the oil from your fingers, when you handle the igniter by the heated end, cause premature failure of the igniter?


Answer-

My assumption, of course, is that when you try to handle it, the "business end" has cooled down or has not been energized at all ( if not , call 911 ). I have a letter from Norton, to me, (dating back to at least 18 or 19 years ago) that flatly states that the oil from your fingers and hands will not cause failure of their "HSI" devices. In fact, the oil will quickly vaporize as the unit heats-up. A popular miss-conception- we hear this story repeatedly and we try to "knock it down " when the opportunity arises.

Code requirements for these igniters specify that they must reach a temperature of a minimum of 1000 degrees Centigrade or 1832 degrees Fahrenheit (with 102 Vac applied) in order to safely ignite gas. The upper limit of 132 Vac will produce a temperature of approximately 3100 degrees F while the normal voltage input of 120 Vac produces approximately 2600 to 2650 degrees F temperature of the Silicon Carbide material used in the manufacture of these units. Safety devices are limited to working between 120 Vac (plus 10% or minus 15 %) or 102 Vac and 132 Vac.

It may also be of interest that (because the Silicon Carbide - in igniter form is quite fragile) the igniter must be handled with care. It also must be noted, for safety's sake, that the ceramic holder remains extremely hot -even when the igniter portion of the unit seems to have cooled. Caution must be exercised when you are checking for contamination on the igniter portion or for cracks or other damage that may have occurred during the life of the device. A brilliant "hot spot" on the igniter, when it is energized, indicates a crack or break in the Silicon Carbide ' If the igniter is used for only ignition purposes (not for both ignition and flame rectification) you may be able to (for a very short period of time) continue to use the "HSI" for only ignition - it's life will be very limited, however. When that condition exists and you are using the "HSI" for both ignition and flame sensing - you MUST replace the igniter with a like device. Flame rectification demands a completely, fault free device, in order to function properly as a flame conductor and sensor.

 

Millivolt and 24 Volt Thermostats Are Different…or Sometimes Not
December 2007 issue

Real world suggestions for the residential Service Technician from Bill Ribble, 40-year Honeywell veteran and controls expert. Bill can be reached at 281-537-2701 or threesons1@peoplepc.com

Question:

My customer had a thermostat problem and he replaced the device with a Honeywell round mercury switch thermostat. He called and said the burner doesn't come on like it should and sometimes it stays on far too long. He called for help. When I got there I found that he had an old, thin, flat, millivolt combination pilot and generator. The pi