Gas Furnace Repeatedly Cycles
I researched this in this help desk and got some good ideas, but none worked. It sounds similar to a dirty flame sensor.
The furnace is forced air gas from mid-1980s. I do not see a manuf on the labeling, but there is a Honeywell control unit.
If I remove the thermostat and just connect the red and white wires together (3 wire controller) the furnace will start and run (so I think it might not be a flame sensor -- but I may be wrong). I thought this indicated that the thermostat was bad and I picked one up and replaced the old one (Hunter, old and new the same model) and it did not solve the problem. (I replace the thermostat about a year ago when the furnace would not turn on at all -- the furnace repair guy wanted to charge $500 to put a new thermostat in!).
The problem:
Blower turns on, flames come one, runs for a couple of minutes, flame goes off, then the furnace fan kicks on. After than runs for a few seconds and it repeats. I checked the power supply and it is 26V AC.
I was not able to find a flame sensor that looked like anything I found on line. I followed wire from the control unit to try to find one. There is a connection to a device next to the igniter. The connection is not a wire, but a rigid metal tube (I did not take the assembly apart to look at the other end because that looked like a major task). But it did not look like what I saw on line.
There a device mounted to the inner sheet metal that looks like a mechanical temperature limits on it. There are wires from the controller to this unit. I think this is what kicks the fan on after the flame turns off. (Is it possible that this also replaces the flame sensor in older furnaces?)
Thanks for help.
Jeff
