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Atwood 8535 IV Jim 1-22-16  
Good ice cold morning all, really really need help. Have a atwood 8535 mark IV (2001)furnace in a fleetwood 5th wheel, please bear with me while I lay this out mice got into blower section, breaking blower wheel, had to replace wheel once wheel replaced unit simply stopped working replaced control board unit fired and ran, until 4 this morning, when it simply would not restart when setting temp, I hear the stat turning on, but nothing else turns on can anyone tell me, what exactly happens and where after the stat calls for heat, which wire do i follow? Is the stat providing power to the black(heat) wire? At the top of the motor I have the on/off switch, than the small breaker, than another small 4 prong device, when following power, I do have power up to this device via the top terminal, however there is no power on the other lugs(when calling for heat or not)
Re: atwood 8535 IV Bubba The Bus Tech 1-22-16  
You didn't say if you have AC of the same thermostat.

Usually when I hear this complaint we tell you to Conect the wires behind the thermostat together to prove the thermostat is good or not. If you have AC that gets a little complicated due to the diferent brands of AC wiring and Diferent ways the AC controls the furnace. YES thats right with the integrated Thermostat the AC control box in the ceiling controls the furnace.

The black 4 wire block is a "Klixon" time delay relay.

The Thermostat turns on the relay, a few seconds later the relay starts the fan motor and provides power to the control board.

The control board "checks" the sail switch to see the fan is up to speed, the furnace is not overheated at the limit switch and after 30 seconds or so opens the gas valve and starts sparking. Once the flame lights the control board measures the Ionized gas in the flame and stops sparking.

So usually if the sail switch does not trigger the fan sits and runs but noting else happens.
If the Limit Switch triggers, the fan runs but no heat until the switch cools off and resets then the thermostat is turned off then back on. The Limit switch can go bad and not reset, usually temporaily fixed by tapping it or by pas it to test with a paper clip or jumper wire.

So the fan wont start, By pass the relay. If the fan starts we need to go back to why didn't the fan cut in? Thermostat, bad ground, No power from AC relay and so on. Imight be a little more descriptive if I know what AC you have.

Good Luck
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