Furnace Confusion

[OldJimi]

I have had some pretty chilly nights since mid Feb, that was the last night that I was able to to set my thermostat to Heat - Gas and the furnace fire up and run.
My '22 3031CK has a Coleman Heatpump/AC, Dometic furnace, and AirXCell thermostats. When the furnace quit, it went through a period of fire/fail starts for a little while, then changed to the blower run for a few minutes and shut off.
I'm to be down south where I could switch to Heat-elect and, between that and the elect F/P I was able to remain comfortable all but the coldest nights.

Warranty service eventually came up with a furnace control board after a few weeks and replacing that enabled the furnace to fire when the sail switch was jumped. Still waiting for a sail switch from Keystone.

The strange part of this is that when it gets really cold, to the point that the heatpump/FP combo won't keep the temp up, the thermostat changes to Heat-Gas/Elect and furnace fires up and runs in conjunction with the heat pump and I get toasty warm air from the floor registers.

I understand this is a feature of the heat pump unit, that's great, but why would it not allow the owner a little control instead of turning it on only when the heat pump detects it is failing to do the job?

It's set up to ensure I get hypothermia before if fires up. I hope the sail switch is a cure, looking to have some springtime in the Rockies soon.

[rohrmann]

If you are really that cold, you might be better off just buying a sail switch. Probably get it is a day or two. https://www.amazon.com/Dometic-33082...e%2C517&sr=1-4

[OldJimi]

I'll wait and save the $25! Mostly, I'm just surprised the the furnace will not run on it's own, but WILL run when it gets a signal from the Heatpump. Although it got down to 30 outside, it was 66 inside when I got up to check that it was indeed the furnace I heard. Seems if the sail switch was necessary for one, it would be necessary for the other. Strange engineering, although a sometime of override to get that furnace heating the belly in an emergency is an excellent idea!

[jsb5717]

First, if it’s below 40 degrees outside then your heat pump isn’t of much use. You will definitely need the gas furnace. So let’s focus on the gas furnace. There are a number of potential causes for those symptoms. But, let’s make sure we understand the symptoms. The sequence of events is important. So what exactly is happening? Do one of the following describe it?

You set the thermostat to call for heat from the furnace and:

1. The fan spins up for a few seconds then quits - if it’s this one then start by replacing the sail switch
2. The fan spins up then you can hear the igniter working. You hear it sparking but it doesn’t ignite. - if it’s this one then the sail switch is fine and there are other possible causes
3. The fan spins up, you can hear the igniter working, the furnace fires for a few seconds then quits. - if it’s this one then again, the sail switch is fine and there are other causes.

Let us know which number represents your symptoms and we’ll take it from there.

[OldJimi]

It progressed 3,2,1 until they replaced the control board. Test bypass of the sail switch and it would not fire up. With the new control board, I can set the Thermostat to Heat- Gas, and the fan comes on and blows cold air for a long time. There are two conditions now where the furnace will fire and run. 1. Put the thermostat on Heat-Elect and the heatpump will run and if it gets cold enough that the heatpump doesn't produce enough heat then the thermostat switches to Heat-Elect/Gas and the furnace will fire up and run while the heat pump is running. 2. Put a jumper across the sail switch, turn the thermostat to Heat-Gas and the furnace will fire up and run.

When it has been running in Gas/Elect mode, if it shuts off and I switch to Heat-Gas afterward, it blows cold air continuous and the furnace doesn't try to fire.

I had a few cold nights where I got to test a bit with the thermostat settings. Heat-Gas/Elect is not a normal option on the thermostat menu, the tech said that option is a signal from the Coleman AC/HP.

I have figured it out enough, I think, that I'm not worried about freezing or having my RV freeze or actually needing to run a space heater or the electric f/p, but though the operation strange enough that maybe it was worth getting written somewhere searchable in case someone else experiences it or has experienced it.

[jsb5717]

If it’s firing and running some times but not others then there has to be a diagnosable reason. My friends furnace was doing that very thing and it turned out to be the furnace propane valve. It wasn’t consistently flowing adequate propane flow to sustain the furnace. We just replaced that valve and it’s worked perfectly.

[OldJimi]

They put in "Smart Circuits" so it's hard for us to understand. You know, I used to adjust the timing and dwell on automobile engines under a shade tree, and, although I'm getting up there in age, I can still remember when phones had only one lens for the camera!

[wed]

The heat pump will not work at real cold temp you need to use furnace

[Muzzbgreen]

I'm looking at a 2019 3855br and when the seller was working the furnace heat pump, only the heat pump would come pn? I put the thermostat at furnace but it wouldn't fire up? I s there a trick to this?

[LeftOverParts]

Was the propane on and not empty?

[Muzzbgreen]

Thats a good question and I really dont know?

[LeftOverParts]

You can ask them to confirm it. Assuming the thermostat is set low enough, if it doesn't fire with propane, you can refer to to JSB5717's post.

[Daryles]

Muzzbgreen,

Here's a good video that explains the operation of the Dometic capacitive touch thermostat.

The OP has the new Coleman system and I agree with him, these "smart" systems can be very problematic when they don't work right. There is no manual override to tell the furnace to operate and leave the heat pump off.

Dometic capacitive touch thermostat operation

https://m.youtube.com/watch?v=DJ0rBMtU9rE

[Muzzbgreen]

Thank you
That video is excellent and explains a lot.
I haven’t talked to the seller but I’m leaning towards the propane tank being turned off since the unit is sitting vacant and we’re in San Diego.

[Daryles]

If the propane tanks vales are off, turn them on really slooooowly to prevent the internal safety shut off valve from tripping shutting off all propane flow.
There is also an Auto Switching valve that automatically switches to the full tank when one runs out. The instructions are in the files section.

[OldJimi]

I finally got the new sail switch installed in my furnace and it works normal again.

[Muzzbgreen]

Good to hear hope that’s the fix on my potential purchase.

[OldJimi]

Thanks, hope it works out well for you!

[OldJimi]

It worked normal until the first time I got into cold weather. Drove through rain and snow, got to a park in Wyoming where I had planned to spend a few days, and set up my rig in barely below freezing weather. I was curious about how my furnace would perform. Turned it on gas, it coughed a couple time and then fired up and ran. It warmed the RV nicely. I woke up in the wee hours to the sound of the furnace blowing coolish air, trying to ignite twice (about 2 sec) then, while blower continued, it would wait for about 12 seconds, the repeat unsuccessful ignition.
I contacted the nearest Camping Worlds, explained the recent contoller and sailswith replacements, and asked if they could send somebody out for warranty maintenance. The sevice manager told me I would have to put up $400 upfront plus $100 upfront for the mobile maintenance...
I found a good on an end of season space heater at Lowe's and am confident we'll survive until we get back to our home base later in the summer - let them pickup where they stopped while I research to see if Florida has any RV lemon laws.

[jsb5717]

Originally Posted by OldJimi

...I woke up in the wee hours to the sound of the furnace blowing coolish air, trying to ignite twice (about 2 sec) then, while blower continued, it would wait for about 12 seconds, the repeat unsuccessful ignition...

Sorry to hear of your furnace woes. Been there! If you're actually hearing it attempt to ignite then you know it's not the sail switch...at least it's working.

Dumb question, but did you confirm that the propane was on? Did you try it with both tanks? Do you open the propane tanks slowly? Is your stove working well?

Sadly, failure to ignite could be a variety of things including propane valve, gas diffuser, and limit switch.