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[Jevad]

BLUF: Furnace not providing 12V to Thermostat, "Fixes" itself with a thump to the side of the RV. Thoughts on what could be wrong?

Atwood/Dometic Model Number AFMD30141/ Part Number 32830

Very new to me/ just purchased a used 2018 Thor Four Winds 30D. We are on our second trip and went to upstate NY in mid-November = COLD and Snow!! Everything seemed to be going well, although woke up to cold coach this morning. I'm having a problem with our Furnace where after working fine for the last 3 days/night, the furnace fails to start/kick on.

Propane is good, Plugged into shore power, also tried on battery and with the chassis running - to make sure it wasn’t a powerline issue - still no luck. I noticed the thermostat wasn’t "clicking", happened to have some tools and pulled out the voltmeter and found no power to the Thermostat. Sliding setting left/right had no effect (no click for thermostat to kick on heat). After checking this forum I saw there was a reset breaker likely on the furnace. (it had been windy… so maybe that triggered something).

I went out started to remove panel over furnace and suddenly it kicked on!! The blower motor spun up, then 30 seconds or so later furnace fired and started as normal. I finished removing the panel and saw the reset switch, everything looked normal, dry, no water (no louvers on this coach that others had water issue), nothing to indicate why it hadnt started. It’s a fairly new coach and all the wiring is in good shape (looks new), and I verified each connection was solid. I Buttoned everything back up and furnace now running worked as expected. It kicked back off when the coach warmed up to temperature as normal.

When a while later we noticed the coach was getting cold again… and once again, nothing - no power on the thermostat. (it had not kicked back on automatically since I touched it last), I went back out and removed the furnace cover panel again, this time it didn’t start on its own as I removed it. Poked around, tried to test Sail switch and burner switch, (Not knowing the normal state of the switchs - I cant find a wiring diagram.) I figured maybe one of the switches might have been stuck, so I tapped the housing, and suddenly the blower motor started (followed by the furnace again as normal).

Again, furnace ran to proper temperature, the thermostat shut down at temp, but again it would not restart the next cycle. After the furnace ran/shut off as normal, I failed to get 12Vdc on the thermostat wires again (between Red 12V and Blue Ground). I went outside this time and decided just to give the outside wall a bang or 2 with my open hand. Went back inside and I now had 12 vdc on the thermostat and was able to run again.

I suspect either a switch or more likely relay is sticking? Any thoughts? (Not sure how/what provides power to thermostat? Relay?). Help!?!

Thank you!!