Furnace problem I Have a 2005 Montana3295RK with a duo-therm air conditioner,suburban sf35f furnace and a dometic thermostat with remote. The problem lies with the furnace. It will not turn on, and in the rare event it does it will not turn off unless you either pull the fuse, turn the switch to the off position on the furnace or turn the gas off at the tanks. I can force the furnace to come on by pulling the fuse and then putting it back in and the thermostat does not have to be in the on position. By doing this if the propane tanks are turned on the furnace will run untill one of the 3 methods mentioned above are done.

The problem is most likely in the control module of the roof air unit. Dometic uses the thermostat to activate and deactivate a relay in the control board of the roof ac unit whiich is just visible when you remove your air intake screen. The two blue with white stripe wires are the furnace control wires.

The furnace turns on and off by the opening and closing of relay. Most likely, the furnace control relay is stuck in the on position. On the thermostate, remove the fur wire and see if the furnace quits afrer it cycles down...it does not quit right away. With the termostat out of the loop, if the furnace does not shut down, the problem is in the control box. They are not hard to replace but you must be careful with the live wiire from the 110 ciucuit breaker. If you are not comfortable with the repair, take it to a dealer. The part number is on the assembly box. They need to know if you have the heat srip option or whatever othert options our Roof AC has. If the furnace still runs with the blue/white wires disconnected, the furnace wires are shorted somewhere between the furnace and the AC control unit.