Originally Posted by tjdavisjr
Hello, We are camping in East Tennessee and it's a little cool in the mornings. I turned the furnace on to make it a little cozier and nothing happens. I can hear a click at the furnace when I turn the thermostat up but the fan does not come on and hence the furnace will not light. I have pulled the cover and looked at the wiring diagram and see that a sail switch controls power to the gas valve so if the fan doesn't come on the furnace will not fire up. Any ideas or suggestions would be appreciated. Oh by the way, if you wait a minute or two after you hear the initial click, you hear another click. It's seems like there may be something resetting after the initial failure of the fan to start.
You are correct; if the fan does not come on, the gas will not flow.
There is power to the furnace through the thermostat because the click you are hearing is the heater control panel resetting to try a second ignition. It will do this 3 times before locking out completely and only recycling the thermostat HEAT OFF; then ON, will get another attempt.
While there is a remote possibility it is loose/corroded wire connection at the motor, gas valve, or the control board, your problem is most likely in the fan motor. It is a common shaft fan motor that provides combustion air to the burner and plenum pressure to close the sail switch and heat the camper.
It can fail for several reasons. The most common are a mud wasp nest on or in the combustion air side of the fan motor that prevents or slows rotation; Rusted/Corroded armature; or thermal switch (internal to motor) open.
You can try blowing compressed air into the exhaust port to dislodge debris/nest; but you most likely will need to disassemble the heater to access the motor.
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