Hello everyone,
I'm grateful for this community and especially for the helpful post from Mark and Lorraine. Their experience mirrored the issues we had with our intermittent furnace. I wanted to share our solution in case it helps others: it was a faulty thermostat-to-AC wire.
Symptoms:
Below ~60°F:
Furnace blower would start, ignite briefly, and then shut off after a few minutes.
Blower would start, ignite, then immediately go out.
Blower would start with no ignition.
In each case, I heard a "click" from a relay in the AC, followed by another "click" as the system shut down. The blower would then enter shutdown mode.
Oddly, stepping on a specific spot near the pantry/seat seemed to trigger the on/off cycle.
Above ~60°F:
Furnace worked perfectly with no issues.
The Fix:
Initially, I suspected temperature-related components and replaced the gas regulator switchover valve and upper-limit switch. This did not resolve the problem, so I changed the sail switch, control board, and thermostat, just to throw everything at it. (I now have spare parts on the ready)
After finding Mark and Lorraine’s post, I confirmed their diagnosis: a faulty thermostat-to-AC wire. Here’s how I fixed it:
Purchased an 18-3 wire from Home Depot.
Removed the interior AC cowling to locate the thermostat wire’s connection to the HVAC control unit.
Disconnected the thermostat and connected a new wire directly to the HVAC control box using compact splicing connectors.
I tested it with this jumper and it worked as expected, without issue.
Fished the new wire with a wire hanger from the HVAC towards the curb side (opposite of factory wire routing), back to the rear compartment, over to the street side, behind the radio and pantry, then down to the thermostat. It was actually really easy to fish the wire around.
Once completed, the furnace worked flawlessly, even in cold temperatures, regardless of where I stood inside or outside the trailer.
I hope this helps someone else!