service and repair
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by G&S Mechanical:
I provide this service to help you solve your problems and so I know what to write about. However I need to make a living so I ask that if you can please make a donation it will help pay the bills and keep me in operation. If you cannot make a donation then I know what it is like to be in that situation all to well.
This Form is to help you solve ignition problems
with your gas burner.
For other systems use the old form.
Eventually I will have 6 forms one for each system.
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Due to overwhelming response if you have a control
wiring or fan control
(fan-won't-shut-off) please review these links and the links on the home page and here first. I will need as much information as you can provide on what you have found so far which will require use of a multi tester (meter) that can measure 24, 120 , 240 volts AC and ohms. For electric furnaces you will need to check your elements and sequencers which may require the use of a clamp on ac ammeter. Like this one being use to check a heatpump current draw at the contactor. If you are unsure of your abilities please seek the help of someone who understands electricity and control wiring. If you have to ask for a place to start then you really need to seek help. I encourage everyone who is technically and mechanically inclined to repair their own equipment but please know when to say when. If you need to ask for a wiring diagram then you do not have the knowledge required to safely troubleshoot your equipment let alone rewire it if components are removed.
Please DO NOT replace or do anything else to your thermostat as a diagnostic, use the test lamps above!!! Contrary to popular myth and belief the thermostat is not "where it all comes from".
To easily see the 24 volt control signal purchase an 1819 light bulb, sockets and clip leads (available at Radio Shack). Connect the lamp with clip leads (do not let the socket conductors touch anything else) from the common side of the control transformer to the "W" terminal from the thermostat or across the gas valve or other 24 volt components you need to test. This test lamp is one of the most powerful testing tools available. You can fasten the socket to your equipment using a #6 self tapping sheet metal screw and leave it connected all the time for monitoring purposes. There are reasons to use a light bulb over a volt meter one is that the light bulb will provide a load on the circuit. You should not use a volt meter to test outputs of electronic controls.
A different (not 1819) 24 volt bulb connected to the gas valve. This is an invaluable testing tool that should be used as a first resort to monitor any 24 volt control signal.
White-Rodgers valves are used OEM. on York, Borg Warner,
Coleman Evcon, Trane/American Standard, Lennox/Airflo, Heil, Carrier/BDP
You will usually find a corresponding 50-A-50-XXX (XXX varies with furnace brand) controller to go with it.
The valve shown is a White-Rodgers 36-E on a York furnace
equipped with an HSI ignition system. This furnace had a dirty flame sensor
(not shown), which would cause the burner to run for about 30 to 45 seconds.
The cure was to clean the flame sensor with sand paper.
Please do not mistake a flame sensor for a Thermocouple which will only be used on a standing pilot system (the pilot is on even when the power is off). A Millivolt system uses a Thermopile and will operate the main valve with no AC power.
I will create some field tests for these systems soon, however checking the electrical characteristics of a flame sensor and its circuitry is usually way above and beyond the ability of someone with even a moderate amount of electronics knowledge.
The White Rodgers 36-E valve has had problems with loose solder connections under the plastic cover (that is why I had the lamp connected). The solution is to take off the cover and resolder the joints. This has been a problem on the valves used for Direct Spark/HSI and the ones used for Intermittent pilot. A valve that is used for intermittent pilot will have three wires designated PV/MV(Common), PV(Pilot-Valve) and MV(Main-Valve), a valve for Direct Spark/HSI/Standing pilot will usually only have two but possibly three depending on the brand of the controller. Test for this problem by whacking the gas pipe with a screwdriver and if the flames go out while the valve stays powered then you have this problem. Other symptoms include the valve working for periods of time and then stopping. In both case power to valve will remain for a few seconds until controller drops out.
Don't dismiss the possibility of a loose wire or connection. Components are not the only things that fail. I have had readers who changed every component (against my strong protest) and the unit still didn't work until they found the loose wire.
I would be in serious legal trouble if I used the "lets see if that fixes it" method (replacing parts as a diagnostic AKA Shot gunning). I expect you not to use it either. There is no "Harry Homeowner" short version to servicing. You will need to follow the same procedures that I follow to get the same results. It is "Stinkin Thinkin" to think that you as a non technical person can get away with less diagnostic effort that I do with over 20+ years of electronic and electrical experience.
Most newer controls will have a status LED (lamp) to indicate operation or failures. Each brand and era of controller will have a different code. You will have to find out what that is. Most units have a code printed on a cover somewhere.
It is human nature to blame the most expensive or readily
visible parts first. Try the simple stuff first.
DEFINITIONS (for the purposes of discussion these definitions are for gas ignition system when used in this context):
Link to page written by engineer for Intel on HSI systems and the combustion blower.
questions please use this form.
To help identify which type of gas furnace system you have please click here first.
Learn about a cracked heat exchanger.
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This text written by: Scott Meenen * G & S Mechanical
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