Furnace Fan Won't Turn Off

[bleckb]

Hi all,

I searched the forum for information, but came up short. If you can provide a link to an answer, happy to have that. Otherwise, here's my trouble:

We have a 2020 2108 DS. For reasons I cannot figure out, the furnace fan won't shut off unless I turn off the 12V power or pull the fuse. If I leave it be, it will run and run and run until the battery is drained. All of the information I find is about furnaces not starting due to the sail switch and the like, but I can find nothing about a fan that won't shut down. Problem started last fall when I had the slideout mechanism replaced. Worked fine before dropping it off. Not since. I am trying to avoid having to head out to the dealer and all the headaches that come with that. Any suggestions? I can handle most repairs myself (having replaced the water heater for instance) so don't mind getting my hands dirty or knuckles bloody.

Thanks,

 

[RayIN]

The thermostat is what tells the fan to run, that's where I'd begin. Next would be the furnace PC board.

 

[Morich]

Once the fan comes on and iar flow is confirmed, the fire should light. Does it do that?
If not, that can be a clue. Is the thermostat possibly set for full time fan?
I might start at the furnace and remove the wire from the thermostat to the board that controls the fan. If the fan continues to run, I might move to thinking the control boardis the problem.
Working on the idea of sorting whether the thermostat, wiring, or board are the problem! Take the thermostat and wiring out of the question, then decide which way to go looking for the problem.
If it appears to be in the furnace, then look online for a troubleshooting guide for the specific furnace you have by brand and model number.

 

[bleckb]

Thanks for the two replies. Fan is on auto and the furnace does not light. I reset the thermostat last night but that had no effect. I'll be going further down the rabbit hole as time allows. Thanks for the guidance.

 

[Morich]

If you have the info, perhaps post up the brand and model number of both the thermostat and furnace and we might get you some better , morte specific wiring infor, ass uming we can find those online.

One point that may help if you begin to look at the thermostat is that they are often wired with a standard "pigtail" attached to it and then if we pull the wires up out of the wall we may find the RV wiring is tied on. often with just simple wire nuts. Not the best for bouncing up and down the road but they are handy to take off to test and put back without a lot of hassle.

 

[powercat_ras]

A RV propane furnace does not have a Fan only mode like the rooftop AC units do. It has 3 electrical wire connections: Positive 12 volts from a 10 amp fuse, Positive 12 volts or open from the RV thermostat (12 volts when thermostat is calling for heat, the furnace uses this as a "signal" and the furnace draws almost no power out of this wire from the thermostat), and negative 12 volts AKA "ground" or "common".

If Winnebago now letter codes their TT wires like they do their motorized units and use the same lettering and color system, then negative 12 volts will be White and use letter code JM, positive fused 12 volts will be yellow and use letter code JB, and the third wire is the one coming from the thermostat, will be yellow and use the letter code JJ.

If you can read +12 betweeb JB and JM and read no volts between JJ and JM yet the fan is running then your furnace is defective and will have to be removed and repaired.

Good luck.

 

[bleckb]

Thanks again for the comments.

The furnace, as is the thermostat, is Dometic. The furnace is the DF series. I'd have to open the panel to find the exact model number.

The thermostat controls both the furnace and the AC. The thermostat user guide says there would be error codes if there were any errors, but it shows none.

I'll get my volt meter on the wires to the thermostat and see what I can learn. If I make the call right away, we should still be under warranty. Fingers crossed on that.