RV Furnace Repair

furnace plug wiring

thermostat leads connect to blue, +DC to red, -DC to yellow

This time of year, I get a good number of questions about furnace repair, a common winter task for anyone who performs RV repair. The first thing do-it-yourselfers want to do is replace the thermostat. It is, after all, right there handy and not too expensive. The only problem is, it is almost never the thermostat and it is very easy to know if it is.

First, if the furnace blower runs, leave the thermostat alone. An active blower means the thermostat is powering the blower relay, end of story.

Second, suppose you turn up the thermostat and nothing happens, what then? Naturally the initial step is to check the fuse for the furnace. You will find it in the breaker box with the other fuses.

If the fuse is good, take off the panel where the furnace is located so you can see the wires to the furnace. You will find a red lead, a yellow lead, and two blue leads. Using a multimeter, check for power between the red 12 VDC+ and the yellow 12 VDC-. You will need more than 10 VDC there or the furnace will not operate. If you have a good fuse and no power, you have a break in the wires somewhere. Usually that means running new wires as getting to the old ones is seldom possible. Running wires in cabinets is a common solution.

If you have power between the red and yellow wires, disconnect the two blue leads from the red and white thermostat wires at the furnace. Be sure to mark them so you know what goes where when you put it all back together. Now tie the two blue leads from the furnace together. Doing this bypasses the thermostat. If the furnace now fires and runs, replace the thermostat. If nothing happens the problem is at the furnace.

Remember, every time you troubleshoot you are simply answering a series of questions and one set of questions always leads to the next. Break diagnosis down into steps and repair is much simpler.

Steve (Mobility RV Service 423.341.8792)

2 thoughts on “RV Furnace Repair

  1. My 25′ (actual body length excluding tongue) travel trailer is extremely well-insulated and has an Atwood 8535 IV DCLP furnace that will run you out in no time. Since I mostly dry camp, I try not to run generator much and must watch propane usage. I also wish the furnace fan didn’t blow so much air (often wakes us at night). I would consider downsizing to a model 8520 as the published amp usage is almost half, and Atwood says it would be a straight-forward switch out (ducting and all). But, they said the fan is the same so it wouldn’t be any quieter. They didn’t know if it would use less propane. Do you have any suggestions for: less amp usage, less propane usage, quieter? I thought of the even smaller 8012, but they said that would be a nightmare to fit up an 8012 in place of an 8500 series. If a call is easier, I am in Montana at 406/381-3672. Thanks, Terry

    • In same run time, the propane usage will be in direct proportion to BTU rating. They hedged because they were not sure the smaller furnace would not run longer. Amp draw for furnace motors varies almost not at all so it will be about the same. Blower noise is endemic to the beast and is due to the design and, yes I agree with them. Fitting an 8012 is possible, but what a nightmare!

      If you want quiet heat with no power draw and high efficiency, install an infrared heater. That should serve your needs nicely.



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