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ejj88 · Mar 2, 2006, 03:31 PM

I am have been noticing the past few days that my furnace is shorting in and out. When the thermostat kicks in, the heating element (I think that is the proper term) shorts in and out. The flame for the heater comes and goes while the fan in running. This is not happening every time the furnace runs but it is happening quite frequently.
This is a natural gas central air unit. I do not have the unit name and model number as I am work right now. Just trying to look for some answers and/or some reasons this is happening and if there is anything that I can do as a DIY'er to fix this.

labman · Mar 2, 2006, 04:43 PM

I don't quite understand what you say is happening. On my gas furnace, the draft blower starts up, then the ignitor, and then the gas. The ignitor then goes off, and the blower comes on after a short delay.

There is a sensor that shuts the gas off if it doesn't detect a gas flame soon after the gas comes on. The ignitor then comes on followed by the gas again. There is also another sensor that shuts off the gas if it over heats because the blower didn't come on. If either sensor is bad, the furnace will cycle through the start up procedure several times before locking out for a while. That may be what you are seeing. The sensors should be cheap and easy to replace. One is near the gas valve. The other is on the heat exchanger. Some furnaces will flash an LED to give a trouble code. That may give you a clue which one is bad. You may need to go to a dealer for your furnace to buy the sensors.

ejj88 · Mar 3, 2006, 08:23 AM

Originally Posted by labman

I don't quite understand what you say is happening. On my gas furnace, the draft blower starts up, then the ignitor, and then the gas. The ignitor then goes off, and the blower comes on after a short delay.

There is a sensor that shuts the gas off if it doesn't detect a gas flame soon after the gas comes on. The ignitor then comes on followed by the gas again. There is also another sensor that shuts off the gas if it over heats because the blower didn't come on. If either sensor is bad, the furnace will cycle through the start up procedure several times before locking out for a while. That may be what you are seeing. The sensors should be cheap and easy to replace. One is near the gas valve. The other is on the heat exchanger. Some furnaces will flash an LED to give a trouble code. That may give you a clue which one is bad. You may need to go to a dealer for your furnace to buy the sensors.

Thanks for your post. I do appreciate your help and am sorry that I cannot provide with a better explanation on what is happening.
It is a Whirlpool furnace/a.c unit. It has not display on it that would show an LED (at least that I can tell). I will try explain what is happening, the thermostat tells the furnace to go, the unit ignites and the flame appears and soon thereafter the blower kicks in. When it is shorting out, there are these clicking sounds while the flames appear and then quickly reappear again. This all happens and after blower is kicked in, the flames are starting and stopping very briefly.
Sometimes it is doing this more than other times. I was thinking that it had something to do with the ignitor but if it is one of these sensors you mentioned, this would be a minor repair. The problem may trying to locate these 2 sensors on the unit and then getting the parts to replace them.

If you are thinking that this is your best guess, if I get you the model number of the unit, would you be able to tell be better where these sensors are on the unit? So I can get the parts and replace them?
THANKS A MILLION FOR YOUR HELP.

labman · Mar 3, 2006, 08:45 AM

Fraid the model number wouldn't help much. It would be a pain to check it, but you need to see if the gas valve has power when the flames go out. If it still has power, it is bad. It would be fairly easy to change, but may take careful adjustment you couldn't do. If the power is going off, either you have a bad sensor, or the control board is bad.