Furnace and Vent Fan Problem

[Meathouse]

Any help diagnosing this issue would be greatly appreciated!

2014 25DS Fr3. Bought brand new with about 13,000 miles on it now.

Have had issues in the past with our furnace not lighting. Took it in under warranty and the dealer couldn't figure it out. A traveling mechanic couldn't figure it out either. We (mechanic) replaced the regulator and turned up the pressure a bit to compensate for the water column and altitude issues here in Colorado and it seemed to fix it but haven't used it all season when only running the 12v system only. Have always been plugged in somewhere.

We were in the mtns this weekend and temps got down in the upper 30's. No shore power so just running 12v but with solar so the batteries are fully charged. Turned on thermostat and furnace and it ran through it's cycles of trying to light about 8 times. The cycle is 3 times and about 10 ignitions, trying to light and then if it doesn't light the fan will turn off and then not try to light again until you turn off the thermostat and start over. On the 9th time of 3 cycles and 10 ignitions each, the furnace lit. I ran it to burn off any dust etc for about 20 minutes then set the temp to come on later in the night and went to bed. It never lit over night.

In the morning I got up and set it to turn on and after about 10 cycles it would not light. I go outside, pull the panel for the furnace off, blow off the dust and just switch the on/off button on the furnace manually while trying to get it to light and basically overriding the thermostat of having to reset it after each cycle if it doesn't light.

I do this for a few cycles and it just wouldn't light. Put the exterior panel back on and went inside to turn off the thermostat and let it reset. Turned it back on and nothing. No furnace and no vent fan. I figure I blew a fuse so I check the interior fuse panel and everything is fine. Go outside and check every fuse on the battery lines and nothing is blown. I open up the main control fuse block on the wall of the battery compartment and find that a 5v fuse on the brown wire is blown and think that's the problem. Nope. Replaced the fuse and nothing. If you pay attention to the way the furnace and vent/AC works, you will turn on the thermostat, listen for the click in the vent/AC unit in the ceiling, then typically the blower fan in the furnace will turn on and then the furnace will try to light. I can hear the click in the vent/AC unit but that's it. No furnace blower. No vent/AC fan, no electronic ignition clicking in the furnace.

I turn on the generator and the vent/AC fan will run on Hi and Low but not when set to automatic. I turn off the generator and the vent/AC fan will not run on Low, High nor Automatic.

I opened up the vent/AC screen in the ceiling and opened the grey control box in there and there are no fuses. I checked the (3) 25v fuses on the converter and they're all good.

I've run out of options in my head.

I don't have a wiring diagram of how the furnace or vent/AC is wired. I've checked every fuse I can find in the RV. I don't know if the furnace is wired directly from the batteries or conversely to the vent/AC unit. I'm not sure if the furnace is wired "first" or the vent/AC is wired "first". Obviously, they are dependent on one another for both of them to work but where is the problem????

I'm home now and plugged into the house and the vent/AC fan will run on Low and High but not automatic and the same problem that the furnace won't come on and the vent/AC fan will not run on automatic when the furnace is turned on.

I've checked all the wiring attaching to the furnace and everything is connected. I did the same in the vent/AC unit in the ceiling and it's all good.

The furnaces in these units are impossible to get to easily. They also don't have a manual light opening like in a pop-up or smaller rig. I've had those kinds and have been able to work on them, move the ignitor closer to the gas etc but this one is going to take some work to remove and work on.

I'm out of warranty and don't want it sitting at an RV dealer for 3 months while they "get to it".

I'm not sure what else to do but anyone that knows how these are wired, would be of great assistance to me!

[Meathouse]

Since I manually turned the furnace on and off while it was "cycling" could I have fried the thermostat for that circuit??

Worse, could I have fried the circuit in the furnace itself??

Again, any help is appreciated.

[wolfgang22]

I had a similar issue earlier this year and I needed to get the circuit board replaced. It drove me crazy trying to trouble shoot because every once in a while it would kick on and work for some time.


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[KansasFR3]

I don't know how the vent/AC is coming into play with your furnace issue, but it probably doesn't run since your in the 30's (no reason to).

Just looking at the furnace issue, last winter I had my furnace not lite one night, and pulled the fuse in the rear bedroom circuit breaker panel for the furnace, which reset the system. After replacing the fuse (which wasn't blown), it reset the circuit board I guess and lit as usual. Haven't had any issues since. So maybe try to remove/reset that aft fuse...Hope it helps.

[Meathouse]

Thank you for suggestion on fuse but tried that. The Ac vent fan typically runs when furnace is on and thermostat fan is set to auto.

The more I've read and the more I understand the way the furnace works, I think it's the thermostat or the time delay relay on the furnace.

After work I'm gonna bypass the thermostat at the furnace (2 blue wires) to see if furnace fan will kick on. If yes, then it's the thermostat. If no, next in line would be the time delay relay, then the sail switch and if all that doesnt work, then it falls to the furnace circuit board itself.

Will update.....

[Meathouse]

Update to the update.

Went to work on the RV furnace this afternoon. Opened up the outside cover, found the 2 blue wires that go to and come from the thermostat. Got them ready to be tested, adjusted/tightened all the other wires coming and going on the furnace, went inside to turn the batteries back on (kill switch), went to the thermostat to turn it to the furnace setting. Hold your breath everyone but as I'm walking back out of test the wires.........the furnace blower comes on. Not only that but as I'm walking outside shaking my head, the freaking furnace lights on the first ignition try. I mean, not even a bunch of ignition tries....the VERY FIRST IGNITION try.

My 6 year old son that was settling in for at least an hours' worth of daddy cursing and throwing stuff says, "ummmmmmmm, it works daddy" then goes back to playing on the ipad. I lean against the wall and feel the beautiful heat exhaust play blow out on my shirt as it's still 88 degrees outside.

Unbelievable.

I've lost sleep and time trying to figure this thing out for 3 days and poof it comes on after I put it in storage for a night.

So.......I'm not sure what happened. I have already ordered a new thermostat as I was sure that's what it was. I was going to order a new sail switch and time delay relay tonight just in case the thermostat wasn't the problem and was looking into the circuit board replacement as well.

My 10 yr old daughter did remind me as I'm telling this story that I might have "accidentally" slapped the top of the furnace in frustration on the first morning that it wouldn't work. And as I recall, it quit working after that but of course my hard head always says, just hit it when all else fails. Oh well.

I now think I must've jiggled a power wire loose somewhere on the circuit board of connections when I was working on it and when I pushed on everything this afternoon, I must've reconnected a loose connection. Shaking my head.

I do believe however that the original reason that the furnace would not light is the altitude at which we were staying.....@ 9,000 feet. The only other time we had problems getting it to light was also @9,000 feet in Telluride. Apparently, the sail switch (located inside our furnace blower fan and on the circuit board side) can be sensitive to the thinner air at altitude and can fail to open up the oxygen/gas mix properly resulting in the furnace not lighting successfully. That's my hypothesis for now and I'm sticking to it.

Thank you to those that posted a response and I hope that my posts will help someone, somewhere down the road with the same problem. This forum has helped me too many times to count so thank you to all and keep posting your issues and solutions!

MJM

[RJJ]

I think sail switch is what mobile tech changed on our Winnebago furnace. We were up near Frisco, CO and furnace wouldn't light. I seem to remember he said there is a wider (?) switch for high altitudes. Never had an issue again after that. About 10 winters in a row up there. Glad it's working for you.


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