Installed Honeywell thermostat, furnace inop

[Iraqvet05]

I replaced a mechanical Coleman Mach thermostat with a Honeywell non-programmable thermostat. I tested out the A/C a few weeks ago and it works fine, even with the toggle switch I added for the fan hi/low setting. When I tried the furnace this weekend, it did not work. The Honeywell displays "heat on" but the furnace does not trigger. I ran the white wire (two wire red and white) to the W position on the thermostat. Where do I start troubleshooting?

[Iraqvet05]

I made it out to the storage lot this morning and tried setting it on electric but still no luck. The DWM I keep in the TT has a dead battery so my electrical troubleshooting did not happen.

[Chris_Bryant]

If you have 12 volts (nominal, of course) at RH, then W should have 12 volts when calling for heat. Make sure W is connected to the "cold" thermostat lead from the furnace. Try setting heat to electric, rather than gas. (or vice versa).

[Iraqvet05]

I have not had a chance to troubleshoot this further and my wiring drawing are in the TT which is in storage. As mentioned, the fan high/low and A/C function perfectly but the furnace does not function at all. I wired the white wire to the W terminal as it should be. It will probably be Sunday before I can drag my battery and multi meter to the TT to look at this again...too many commitments with my kid's sports, school and scouting are cutting into my play time. 🙂

[downtheroad]

I sometimes think it would be nice if the original poster would come back and report what happened with the suggestions that the rest of us took time to offer.....

(as they say, ) "Just sayin'"

[Old-Biscuit]

Coleman Mach to Honeywell

Coleman

Red = +12vdc
Blue = -12vdc
Green = Fan High
Gray = Fan Low
White = Furnace
Yellow= Compressor

Honeywell

Red = +12vdc to RC/RH
Blue = -12vdc NOT USED
Green = Fan High
Gray = Fan Low
White = Furnace
Yellow= Compressor

[Dutch_12078]

My Honeywell stats are wired as shown, and work well for both heating and cooling.

[Iraqvet05]

WyoTraveler, we rarely use the furnace but it worked this spring on the old thermostat. I agree that the wiring can be an issue and I'll double check continuity from the furnace to the thermostat. I found a few bad connections behind my distribution panel when I installed an EMS last year.

[WyoTraveler]

I didn't add or replace a themostat on my 2012 Jayco 19RD TT but when I had problems with my TT (It almost burned up about 4 months after buying it new) Jayco wouldn't cover under warranty but that is another story. I had a local dealer repair it. They pulled the A/C and furnace and bench tested everything. Then pulled out all the connecting wires and replaced them. The local dealer said it was the worst wiring job in a TT they had ever seen. Wire colors didn't match, no wire nuts, crimp connectors or tape on wire connections within the walls. A lot of those bad connections were found in the wall. I didn't have any more problems once the dealer replaced all of the bad wiring. I have no way of knowing if this was a one of a kind sloppy wiring job or SOP. As you can see I no longer own the 2012 Jayco 19RD TT.

If the replaced thermostat isn't working you may want to trace out all of the wiring.

[Iraqvet05]

I don't have the wiring color info with me but researched this well and took pictures before I disconnected everything. My Jayco had two separate wire looms in the wall and they didn't match color for color to the Coleman but I believe I wired everything to the RV industry standard (?) based on the Coleman:

Red = +12vdc
Blue = -12vdc
Green = Fan High
Gray = Fan Low
White = Furnace
Yellow= Compressor

I'll have to check the temp setting as Downtheroad suggested and see if the W is triggering 12Vs. The RH/RC terminals are bridged.

[wnjj]

What other wire colors are there and what other terminals are on the thermostat?

All the thermostat needs to do is send 12V down the white wire via a relay. Usually there's a power wire connected to to R or RH that provides the power to one terminal of the relay. If you temporarily touch the white wire directly to that it should start the furnace, bypassing the relay.

[downtheroad]

Same thing happened to me when I first replaced our stat.
After much head scratching and tinkering, I realized that I had not set the temp high enough (higher than the ambient temp) to trigger the furnace....:S

Not saying that this is what is going on with yours...but???