Can a broken wiring harness affect the furnace fan?

[ryanbirch]

Hey guys,

Long time lurker.. first time poster.

Is there any chance that a broken wiring harness from the trailer to the truck could cause the furnace fan to run constantly?

Back story.. I have a 1988 Terry Resort 245 5th wheel trailer. When I put it into storage after the last camping trip last fall, I was tired and rushing and pulled away with the wiring harness still plugged into the truck.. frustrating. It seems one of the previous owners jerry-rigged the wiring harness a bit, and some of the "spliced wires" pulled apart.. I didn't think much of it, and said "I'll re-wire it in the springtime".
A few weeks later I went up there to winterize the trailer, and as soon as I connected the battery, the furnace fan started running. No matter what I do with the thermostat, the fan stays running.

I don't understand what the connection could be between the two, but the furnace/fan/thermostat were working fine before, then I made my tired mistake, and now this is happening. So it must be related somehow? Perhaps the broken wiring is affecting the thermostat itself, which in turn is causing the fan to run?

Any suggestions or advice? I have the trailer up for sale now and would like to fix this before I sell it. I'm going up today after work to grab it, and I'm hoping that when I splice the wires back together things will start working properly again.. but I thought I'd post a thread about it as well to get some input.

Thanks folks!
Ryan

[ryanbirch]

Alright.. so I went and picked it up from storage.. plugged the battery in and the fan didn't come on this time. I decided to take the thermostat off, and re-tighten the wires (it just has 2 - red & white). Tested turning it on and off and it's working fine again. Not sure what to say.. maybe last time I wasn't being patient enough and not waiting long enough for it to shut off or something. ANYWAYS... thanks for all the input!

When searching around the forums for similar issues I did come across a few of the threads about switching to a digital thermostat.. as the poster above mentioned. So I think I'm going to do that anyways. Nice little upgrade for only $20, and I think any potential buyers would like that option.

[SailingOn]

Sounds like a good time to put in a new digital thermostat. They're inexpensive, more precise, easier to adjust. See this link. Don't search for an RV thermostat, a residential model from your local hardware store will work well.

[laknox]

ryanbirch wrote:
Thanks guys. Just seems so strange to me that the thermostat/furnace were working on the last trip of the year, but then this started happening a couple weeks later when I went to winterize it. Oh well.. coincidence I guess.

I'll make sure to let you guys know how it goes. Thanks for the input!

Y'know, you =could= have shorted a wire when you pulled off with the cord attached and it simply fried the t-stat. :h Just sayin'...

Lyle

[Old-Biscuit]

Vulcan Rider wrote:

wrgrs50s wrote:

I would guess, you have a thermostat issue as suggested earlier.

Most furnaces run the fan ONLY after the heat exchanger gets hot.
If that is the way it works normally, then there is a thermocouple that actually switches the fan on and off.

There is also a switch on the stat to manually run the fan.
Could it be in the wrong position ??

The problem could be either place.

SOME older furnaces use that scheme...fan comes on after heat exchanger gets hot. Fan switch could be stuck closed. IF that is type of furnace OP has.

If OPs furnace turns fan on to purge combustion chamber before firing off then t-stat is usually bad when fan runs continuously

And always......fan in on position at t-stat (I always like this one cause fix is easy :B )

[Vulcan_Rider]

wrgrs50s wrote:

I would guess, you have a thermostat issue as suggested earlier.

Most furnaces run the fan ONLY after the heat exchanger gets hot.
If that is the way it works normally, then there is a thermocouple that actually switches the fan on and off.

There is also a switch on the stat to manually run the fan.
Could it be in the wrong position ??

The problem could be either place.

[Old-Biscuit]

newman fulltimer wrote:
You have a bad thermastat

THIS^^^^^^

[ryanbirch]

Thanks guys. Just seems so strange to me that the thermostat/furnace were working on the last trip of the year, but then this started happening a couple weeks later when I went to winterize it. Oh well.. coincidence I guess.

I'll make sure to let you guys know how it goes. Thanks for the input!

[wrgrs50s]

Highly unlikely, as usually the harness only supplies voltage to exterior lights, tail, liscense plate, side markers, brakes, etc. Nothing to the interior 12 volt systems.

I would guess, you have a thermostat issue as suggested earlier.

Let us know what you find, I'm very curious.

[newman_fulltime]

You have a bad thermastat

[ScottG]

No.

[donn0128]

Not likely! From the converter fuse panel there will be a fuse marked furnace. From there will be a wire to the furnace fan motor. The thermostat controls on off function