Coleman Gas Furnace - Not working :(

[glitter_sno]

Hello all! I have a Coleman Gas Furnace that is not working. For a while the problem was intermittent, but now it completely quit. The thermostat is working properly, sending the furnace the signal to heat. The sensors and the igniter are working. The igniter glows and is ready for the gas valve to open. You hear a click in the control module and the gas valve does not turn on and the igniter shuts down. We are torn between the control module and the gas valve being defective. Any help would be very appreciated.

[trader4]

Put a VOM on the wires going to the gas valve. If it gets voltage when it's supposed to open, then it's the valve. No voltage, then it's something else, most likely the controller. I'd also measure the voltage with the wires disconnected, because if the valve solenoid is shorted you could read zero or low voltage due to the short. Voltage is usually 24V.

[Ken]

I agree with your answer, but I would add that it is not uncommon for the coil on the gas valve to open up. He could put an ohm meter on the coil connection with one wire removed to check the coil. I have had at least two valves that had open coils.

[Tony Hwang]

Hi, No trouble code? Or valve coil is shot or no voltage to it when it supposes to,

[clare]

I'd be very suspicious of a plugged inlet screen in the gas valve, but it should be relatively easy to determine if power is being delivered to the gas valve by the control board.

[clare]

I would do the opposite - I'd test it with the valve connected, because a high resistance connection would still show full voltage when disconnected - and would show low or no voltage when connected. A shorted solenoid is a much less likely situation - and can easily be tested for with an ohm-meter.

[The Daring Dufas]

Would you happen to have the model number of your furnace? I may be able to look up the wiring diagram or service manual online. If your furnace is a later model, the problem could be something as simple as a Klixon temperature sensor with a manual reset button. I found a good example picture showing what a manual reset safety sensor looks like and you'll notice the reset button between the Faston terminals. The one you have may have a smaller black button and there may be several mounted in different places inside the burner cover.

TDD

[glitter_sno]

The model number is: 7970-656/D One thing my husband did do, he hooked up a power supply to the gas valve while it was going through the cycle and it opened to allow gas into the burning chamber. The meter says it is getting voltage, so I am rather confused. Thank you all for trying to help, you have no idea how much I appreciate it.

[trader4]

Maybe the volts from the power supply spin clockwise while the volts from the control board spin counter-clockwise? Could be the valve was made for Australia.

[clare]

Was it connected when you checked the voltage? Like I said in a previous post - a high resistance connection in the control circuit will show full voltage when open circuit, and low or no voltage when connected to the load (solenoid coil).I'm suspicious you have a cold solder joint somewhere on the control board

[Stormin Mormon]

You might have the skills to troubleshoot, and see if power is being delivered to the gas valve. That will help with the diagnosis.