Dead furnace

Well, the thermostat works for every thing but the furnace.  I've tried shorting it every way that makes any sense at all.  The furnace wire to the thermostat ground wire does make a barely audible muffled little click at the furnace, but still no heat or furnace fan.

Any other thoughts?  Does it seem prudent to replace the thermostat still?

TT

Originally posted by techntrek  Have you checked all of the fuses to make sure the one for the furnace isn't blown?  I also just read there is likely a circuit breaker either under the front cover of the furnace or behind the furnace (don't know why it would be back there).

The only fuse I know about is the 7.5 amp fuse in the main fuse panel and it's fine.  All the fuses there are fine.  I have the cover off the furnace, and don't see another fuse.  There is a black button thing that I think is hooked straight to the thermocouple.  It's pushable but doesn't do anything for me.  There is a circuit board at the furnace, mounted sideways, at right angles to the front of the furnace.  I can see an off/on switch on there that is on, but without pulling the furnace, I don't see how to access the circuit board.  That would mean disconnecting the LP copper pipe, which seems like a last resort to me.  And the furnace definitely won't work with no LP, so other than something very obvious like a blown fuse, there's not a lot of point in my pulling the furnace out.

If we know there is a fuse there it might be worth it.  I'll see what the manual for the furnace says about that.  The manual has not been much help so far though.

TT

Yup, if jumping those same 2 wires at the thermostat didn't work I agree it is a wiring issue.  If you can't easily run new wires to the original thermostat you could mount a dedicated thermostat near the furnace.  Just not too close or it will cycle on/off too often and leave the rest of the camper too cold.

The furnace is up and running again.  It was a broken thermostat wire.  I determined that there was no continuity in the red thermostat wire so I started at the furnace end and pulled a new pair of wires through with the old wire roughly to the thermostat.

This is where it gets kind of interesting.  The thermostat wires from the furnace do not go to the thermostat.  No, they go to the air conditioner.  It's a red and white pair that goes from the furnace to the air conditioner, then a 6-wire thermostat cable goes from the air con to the thermostat.  You can't check the continuity from the furnace to the thermostat.  You can check it from the furnace to the air con and from the air con to the thermostat.  The long run with the most bends is the one from the furnace to the air con, so that's what I checked first.

For the most part, pulling the wire pair along the existing chase was fairly routine.  The cable anchor straps, mostly where the wires turn, were the trouble spots.  All of them were doable though, except the one above the ceiling and the lower portion of the air conditioner, where the wire goes from the air conditioner, above the ceiling, over a little then down between the shower stall and the wall outside the shower.  I could sort of pull the wire down a little way, so that the end would move up out of the air conditioner, but it would not move at all if I tried to pull it up from the floor, over the ceiling and down into the air conditioner.  That's why I pulled from the furnace to about the thermostat.  I spliced the new wire to the old wire more or less behind the thermostat.

I had to loosen the paneling on the wall with the thermostat to make any of this work.  Actually, in hindsight, I guess I could have spliced under the shower if I'd known in advance where the break in the wire was.

I did find the wire break.  As of now I don't know where it was in the run of wire.  I'll see if I can get a good idea when I do the rest of my cleanup tomorrow and put away my tools.  It shouldn't be too hard to get a good idea by laying the old wire out along its old path.

I was surprised that the thermostat was not directly connected to the furnace.  There's bound to be a good reason, but I have no idea what it is.  I think you could run a two-wire, dedicated thermostat to the furnace, and that would have been marginally easier, but then I would have had two thermostats (and would have been able to run the air con and the furnace at the same time).

None of this overall task was particularly difficult but it would have been much more straight forward if Forest River provided some schematics and better manuals.  After carefully reading the manual for the "air handler", I discovered the thing about the furnace wires going to the air conditioner, but I still had no clue whether they went to the inside portion of the air conditioner or the part up on the roof.  I took the cover off the roof portion looking for wires that weren't there and I still have to get up there tomorrow to put the cover back on.  Thankfully there is no rain in the forecast.

TT

I had a hauntingly similar issue last summer with my 173. I had the thermostat replaced, it worked once, then same issue all over again. I took it to my local RV repair place, they couldn't find anything wrong, so finally took the inside cover off the ac unit and found two a loose wire nut there that came from the thermostat. Problem solved?? It worked when I put it away for the cold Colorado winter. Will know more in April when I take it out of winter storage.