Suburban SF-35VHFQ Furnace diagnosis

[Retired wrench]

The furnace in my 2024 310GK stopped working. This 5th wheel is equipped with a heat pump built into the ac unit. There is no reaction at all at the furnace when calling for gas heat. There is 12volts at the circuit board, and the blower will run if power is applied to it. The board has been replaced. No change. I'm not sure where to look next. The limit switch is difficult to access, and I'm not sure if it would cause this problem. The thermostat has very fine wires, and it works the ac and heat pump okay. Help.

 

[Bungy]

The furnace in my 2024 310GK stopped working. This 5th wheel is equipped with a heat pump built into the ac unit. There is no reaction at all at the furnace when calling for gas heat. There is 12volts at the circuit board, and the blower will run if power is applied to it. The board has been replaced. No change. I'm not sure where to look next. The limit switch is difficult to access, and I'm not sure if it would cause this problem. The thermostat has very fine wires, and it works the ac and heat pump okay. Help.

Propane full?

 

[LanerC]

could be the limit switch, i had one go out once, or the sail switch.

 

[Retired wrench]

Propane full?

Yes, the propane is full. The problem is the blower will not run. When I hot wire it the sail switch activates. I'm just not sure if the limit switch stops power to the blower through the circuit board. I'm not good at reading wiring diagrams. Also, might the board in the ac unit be the problem? This unit has a heat pump in the roof unit. We're dry camping at Lost Dutchman S.P. in AZ. Limited generator hours and cold nights.

 

[Retired wrench]

PS: When I said the thermostat wires were fine, I meant they're very thin wires. I think they might control the furnace through a connection/board in the ac unit.

 

[pengle]

Here is a Service Manual for the furnace. Troubleshooting starts on page 30. Page 31 explains in detail "what happens next?, and then?, and then what?".

 

[Retired wrench]

Thanks for the service manual. It's a great help. So, my system has a blue wire with a white tracer which has battery voltage. My solid blue wire had zero volts. When I connect the blue/white to the solid blue, the furnace works correctly. so I assume the limit switch and board, etc are okay. Remembering that I have a Coleman ac with a heat pump, how do I determine if it's the wall thermostat or the silver box in the Coleman ac that's at fault. And again, thank you!