Furnace problem

[jd65]

Just returned from a trip to Oregon where the weather suddenly turned unseasonably cold. Furnace worked fine for a couple of days, then the blower wouldn't come on. A mobile RV repair guy came out, checked it thoroughly, and couldn't find anything wrong. Circuit board, switches, gas supply, thermostat, etc., were all fine. He put it back together and it worked...for a day. Worked off and on, but after a very cold night (low in the 20s), we pulled up stakes and headed home. Any ideas before I take it into our local RV repair place?

[Iowa Dave]

Does it have a thermocouple or other device that could be intermittent in its operation? On regular older house furnaces that was often a problem and was not hard or expensive to replace. Maybe your sail switch needs replacement if the unit is not
Being signaled that it has purged before going to full on heat? I’m not that familiar with these furnaces as I’ve not had a problem with either of ours. Assuming you have plenty of propane at the proper pressure also?
Iowa Dave

[Brian B-P]

A thermocouple might be the culprit if the flame wouldn't stay on, but not for the fan. A sail switch might be the culprit if the flame wouldn't start, but the fan would still run until a timer expired. Propane doesn't matter until the furnace attempts to light, after the purge cycle.

If the thermostat is calling for heat and fan doesn't even start to turn, this sounds like a control electronics issue.

[steve dunham]

Check the sail switch . The sails switch must be in the open or off position when the heat cycle starts . When the fan starts the sail switch must go to the on or closed position in order to prove purge and start the ignition cycle . At the end of the heating cycle the fan should stop and the sail switch should return to the open or off position
This is a safety feature to insure proper purging of the furnace . That’s why you can’t just jumper out a bad or stuck sail switch
The fan will not start if the sail switch is stuck in the on position when the tstat calls for heat
I am going off memory and my memory is not as good as it use to be

[davescape]

Do you have the digital Dometic thermostat? We reprogrammed our's to have a smaller temperature differential (it reacts smaller temperature changes) and that seems to have messed with its brain. I set it back to the factory setting and I think (maybe hope) that will have fixed the strange behaviour.

[Bill and Earline]

jd,

We had somewhat similar symptoms: Worked fine for several cycles, but then wouldn't light--therefore cold. Blower would come on for 10 seconds or so, then stop without lighting.

I took it apart enough to get compressed air on the sail switch to supposedly clean it, in case that was the problem. Put it back together and again intermittent failures to light.

Took it all apart and replaced the sail switch, which is a bit of a pain in the year model we have, but it seemed to cure the problem. Will know for sure this week.

If you respond, please be more specific about exactly what your does or doesn't do. The more experienced folks on here have great knowledge.

Bill

[Greg and Kathy]

Originally Posted by jd65

Just returned from a trip to Oregon where the weather suddenly turned unseasonably cold. Furnace worked fine for a couple of days, then the blower wouldn't come on. A mobile RV repair guy came out, checked it thoroughly, and couldn't find anything wrong. Circuit board, switches, gas supply, thermostat, etc., were all fine. He put it back together and it worked...for a day. Worked off and on, but after a very cold night (low in the 20s), we pulled up stakes and headed home. Any ideas before I take it into our local RV repair place?

Need more info, type of thermostat, what exactly happens when you turn up stat etc

[jd65]

Originally Posted by Greg and Kathy

Need more info, type of thermostat, what exactly happens when you turn up stat etc

We have a Dometric digital thermostat which has always worked fine. It works with the A/C and fan, and before this trip, with the furnace consistently. The problem is that our furnace blower does not come on as it should when the thermostat is set for a warmer temp. With no blower, the sail switch is not engaged so the heating element does not come on. When the blower does work, the heating element kicks in normally. The problem lies with the blower not always coming on when it should. Sometimes it works, sometimes it doesn't.

[sjnuss]

Originally Posted by jd65

Sometimes it works, sometimes it doesn't.

Curious to know if this is happening when plugged in and/or running off the batteries. We are having a similar issue but only appears to be happening when running off the batteries. When plugged in the furnace works just fine. In discussion with Escape they are suggesting to check the gas pressure. I haven't been able to do that yet but will do so in the next few weeks.

Steve

[jd65]

Steve,
It happened when we were plugged into shore power in an RV park. No other electrical issues. Don't see how the gas pressure could affect it, as the gas burner doesn't come on until after the blower motor runs long enough to activate the sail switch. Our blower not coming on in the first place is the problem.

[Greg and Kathy]

Originally Posted by jd65

We have a Dometric digital thermostat which has always worked fine. It works with the A/C and fan, and before this trip, with the furnace consistently. The problem is that our furnace blower does not come on as it should when the thermostat is set for a warmer temp. With no blower, the sail switch is not engaged so the heating element does not come on. When the blower does work, the heating element kicks in normally. The problem lies with the blower not always coming on when it should. Sometimes it works, sometimes it doesn't.

I have no A/C so the simple thermostat, same symptom. Removed the thermostat and jumpered the2 wires that go to furnace and fired up ok so proved bad thermostat. I don’t know the digital stat wiring so not much I can tell you. Sounds like bad Stat