We have a 5th wheel trailer that has a propane furnace in it. Usually when you turn it on, if the thermostat is up, the fan comes on right away and then about 30 seconds later the propane comes on and is ignited and then lots of heat flows from the vents.
About 3 weeks ago the furnace suddenly stopped working. The only thing that happened when it was turned on (with thermostat up) was a clicking sound from the furnace.
First, I took off the grille and furnace front cover and I could easily spin the fan by poking in a long stick, so I knew the fan motor wasn’t seized. I removed the furnace (not a particularly easy task as it appears when the trailer was built, they did not have it in mind that someone might ever want to remove the furnace). Then I was able to check and found that the furnace was getting 12 volts (and ground) as required and also that the thermostat and related wiring were working as they should, so the problem was definitely inside the furnace.
I hooked the furnace up to a 12-volt battery so I could do some trouble shooting. Luckily there is a wiring diagram glued to the furnace and the controls are pretty simple, so it didn’t take too long to isolate the problem to the control board (it was getting all the correct inputs – power, ground, signal from thermostat, connection to sail switch (to sense when the fan is spinning) and over-temp switch, and the outputs to the fan motor, propane valve and spark ignitor were all connected. I could fake that the fan was working by moving the sail switch by hand and everything else worked as it should, plus when I put power to the fan output wire the fan spun just fine. It turned out the fan relay was clicking when it should but no power was getting to the fan.
I ordered a new control board from an RV place (about $140 CDN) but then as I was looking at the board I noticed that one of the 4 connectors where the relay pins were soldered to the circuit board looked weird, there was a dark ring around the pin. I re-soldered the pin to the circuit board trace and tested the furnace and it worked perfectly. Luckily, I was able to cancel the order for the new control board.
It has now been 2 weeks since the repair was made and the furnace reinstalled in the trailer and so far, it is working perfectly. I find repairing this sort of thing to be very rewarding. Not just as I saved money avoiding having an RV technician make a house call, or purchasing a new furnace or new control board but also as I like to get as much life out of things as I can… sort of my way of fighting back against our ‘disposable’ society.
Now we just need to get the “right to repair” laws in place in Canada so companies like John Deere and Apple don’t intentionally make it impossible for consumers to do their own repairs.
Note: Youtube made this job far easier than it would have been otherwise as I found a video of a guy completely disassembling a Suburban SF-30 furnace so I knew all the parts of the system, where they were and what they did. I also saw a video of a guy troubleshooting a similar issue on the SF-30.
PS – next thing to fix is the 2004 Golf (2 litre gas engine) which has an intermittent miss, super obvious immediately after starting and then intermittently (seemingly randomly) when under load. Unfortunately that is unlikely to be as easy to sort out as this furnace was.