Suburban Furnace SF42

[TampaSean]

Hi Everyone

We currently have our RV out of storage and plugged in at home in driveway. I went out to the RV the other day and heard the furnace running. Went inside and the coach was hotter than hell (furnace putting out all kinds of heat) from it being on for a substantial amount of time.

That would be great if the thermostat was set to heat- it was not. It was completely off. The furnace just keeps running unless I take the fuse out which then cuts all power to the front thermostat. The minute I put the fuse back in, there is a delay and then it automatically kicks on, ignites and blows hot air until I pull fuse again.

Any ideas on what the issue may be or where to start troubleshooting?

Thanks in advance
Sean

[TampaSean]

Hi All-

Continuing to battle this Tstat-Furnace issue. Now I have no power at the Thermostat. I put in old relay and am now getting 13.1v at both blue wires (at furnace) but that is it. If I jump the blue/red to the motor (red wire), motor runs. Still not getting any power back up to the thermostat. Really not certain where to look now so any guidance is appreciated.

Thanks!
Sean

[TampaSean]

Hi All.

Finally had a chance to get out there and test. New digital Coleman t-stat and replaced time delay relay. Tested and when in Heat, furnace works properly- proper delay and fire. Turn off heat at T-stat and it shuts off. All of a sudden it now starts cycling the fan- does not fire furnace but fan will cycle on and off randomly...could that indicate control board?

Thanks
Sean

[DrewE]

It could also be a short in the control wire to the thermostat, or possibly a failure of the furnace control board. If disconnecting the thermostat wire as suggested by Todd doesn't help, I'd try disconnecting the control wire at the furnace end (which may well not be very easy to get at) and seeing what happens. If the furnace doesn't run, it's clearly the wire; if it does, it's some problem with the furnace itself.

If the thermostat (or furnace) is in a slide, one possible point of failure for the wire is the segment that moves when the slide is moved.

[Toddupton]

Bad thermostat pull the red or white wire off the stat and see if it stops