Thermostat/ furnace issues

[Handell35]

I’ve been troubleshooting my thermostat setup for a few days with no success. Initially, I tried replacing my original Coleman Mach thermostat with a cheaper one from Amazon, but it didn’t work well, so I purchased another Coleman Mach thermostat. Unfortunately, I didn’t take any pictures before removing the original thermostat.


Wiring Details:

• I have four wires in a brown sleeve that I believe come from the air conditioner.
• There’s a small red and white wire that I believe is the 12V power source and ground.
• I also have a thicker gauge white wire that I assume is for the furnace.

Current Setup:

• Air Conditioning Wires:
  • Red to Y
  • Green to GH
  • White to GL
  • Blue to B
• 12V Wires:
  • Red to R
  • White to B (this also connects to the B terminal for the A/C)
• Furnace Wire:
  • Thicker white wire connected to the furnace

The A/C works fine, but the furnace does nothing. I even tried connecting the 12V power directly to the furnace, but that only trips the thermal overload switch.


My camper is a 2004 Jayco (exact model unknown). Any guidance would be greatly appreciated. I’ve attached some photos for reference.

 

[RayIN]

The OEM LP furnace works by simply applying 12V to the furnace. You can run the furnace by simply connecting the 12V + and - together. It will run until the wires are disconnected.
If it runs that way, it proves the thermostat and or wiring is the problem.
I assume you've already exhausted the Jaycoowners.com forums.

 

[Handell35]

The OEM LP furnace works by simply applying 12V to the furnace. You can run the furnace by simply connecting the 12V + and - together. It will run until the wires are disconnected.
If it runs that way, it proves the thermostat and or wiring is the problem.
I assume you've already exhausted the Jaycoowners.com forums.

Yes I can make the furnace run by connecting red and white wires on furnace. I just cannot get both systems to work on a thermostat.

 

[Kirk]

In most cases, when the thermostat serves both the air conditioner and the furnace, all of the wires from the thermostat go to a control circuit board that is in the air conditioner and the thermostat leads from the furnace go there as well. I'm not familiar with the thermostat you are using so would need a wire diagram for it to be able to help.

 

[RayIN]

I must have missed it; what is the model# of your Coleman thermostat?