1984 Winnebago Chieftain 22 Furnace

[Rodney Behrens]

Hi we have a 1984 Winnebago Chieftain with a suburban furnace, the furnace heats to set temp and shuts down. Then it starts to cycle on for 5 secs. then off for 5 secs. it does this around 5 or 6 times then shuts down completely until asked for heat and it repeats. Any help would welcomed. thanks, Rodney.   

[Rich Thomas]

I just went back and looked at the wiring diagram for my furnace. IT"S BEEN a While. On my fan circuit the thermostat relay closes and the fan turns on. This allows the sail switch N.O. to close and puts power through the temp. limit switch to the Module board. That in turn powers the gas valve and ignites the furnace. after heat is applied to the N.O. fan switch it closes and creates a seal in circuit around the Thermostat relay. Once The room temp is reached the thermostat relay opens removing power from the gas valve thru the Module board. the flame goes out but the fan remains on until the fan switch cools and opens up. at that point the sail switch re turns to its normal state N.O. and the whole circuit is ready for the next cycle when the room cools and the thermostat closes to start the whole thing over again.  If your not getting the fan at all check the thermostat and the thermostat relay. if you short out the ( in my case the red and yellow) thermostat wires and the fan dose not  turn on check for 12 volts across the two wires while separated. if voltage is present move on to the thermostat relay on the furnace. Mine is in the upper left corner and is a silver can. My guess is it is bad. pull the wires and read continuity across No.1& 3. Infinite = an open coil. of course  if you jump the two wires at the thermostat and the fan runs the thermostat is the culprit. I hope this helps some I guess it's contingent on how alike our furnace is. And for safety sake make sure to turn off the gas and wear safety glasses when ever working on live power no matter how small.     

[Rodney Behrens]

Hi Rich, The furnace works fine, it's after the heating cycle is complete is where problem starts.The fan cycles on and off after reaching temp and the fan switch has opened.

[Rich Thomas]

That being the case Rodney, I think that takes you right back to the thermostat. It's the only thing in the circuit that will turn the fan on after the cycle is complete. I think I paid like $12.00 for the one I got. There is some adjustment that can be made at the thermostat that compensates for the load required by the gas valve but I think maybe the bi metal spring is worn out on yours. like it takes a bounce or two when its changing state as it cools.

[david craft]

there is no fan switch, just a relay. so the relay cant be open and have the motor run. I agree with rich. just do the relay.