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08-29-2019, 06:35 PM #1
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furnace come on when TT is plugged in
Hi, Could not find this in any other post, but hoping someone can give me an idea of what is happening. When my TT is plugged in after we park it, or if I undo the shore power and plug it back in my furnace comes on and runs. The thermostat does not seem to have any effect and the furnace keeps running. I can actually turn on the AC while its running and both will run. I noticed a slight electrical smell while working around the trailer, but could not pin it down and it seemed to come from under the slide. This is on a 2019 297RSTS that we bought used, hence I have no warranty on it. It appeared to work fine on the dealers lot at the time we bought it, but I wasn't there when it was plugged into shore power at that time and I have never in near forty years of RVs had anything like this happen. Any idea what is going on? where I should look? It is a Suburban SFV-35Q furnance.
Last edited by jdmert; 08-29-2019 at 07:32 PM. Reason: left out info
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08-30-2019, 09:34 PM #2
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I’m totally throwing darts... it sounds like ur thermostat is not commanding the furnace and or the AC properly.
If it’s like mine a dometic thermostat you might try re initializing the thermostat maybe someone put a new one in and did not do this.
I left the sheet in my trailer
But I think it goes like this
Turn mode button to off
Hold + then press mode for 3 seconds until - - shows up
The press mode to complete
I’m going by memory here but it won’t hurt to try it!
If you do the same thing but hold the - button instead you can switch ur temp DP from 1 degree to 2 degrees
The do will come up then use the + - to toggle between 1 or 2
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08-30-2019, 09:41 PM #3
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Thank you Overkill I did not know there was a way to reset the tstat. I will try that also when I get back home. Luckily the weather is such that I don't need the furnace. The fans and AC seem to work fine so mama is happy and not to hot.
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08-30-2019, 10:15 PM #4
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I’m no expert but my understanding is it connects the ac and the furnace via the modular box that’s in ur ac unit, mine was clicking randomly, I did this reset and I think it solved my problem but I won’t really know until next year when we get out again.
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09-03-2019, 04:09 PM #5
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Ok, I have had some time to look at this. 1st off, the smell I was smelling was actually coming from the refrigerator, I imagine burning off the new and the breeze in the corner of the house where the rig sits was bringing the smell to me from under the trailer.
Anyway. the furnace. I could not find any wires that looked compromised. I cannot see some in the wall so it there is a problem there I will need a boroscope. I find that the furnace will start as I said when the rig is plugged into shore power. But after that it did not shut down in what I thought a reasonable amount of time considering the temp was set about 20 degrees below the interior temp. I finally turned off the propane to the unit and it ran on for a bit then shut down. About right for cooling the heating chamber.
I let every thing settle a couple of hours and tried to restart the furnace via the thermostat, no go. propane was back on. I played with the tstat some and can see it 'blink' out when pushed right. When I run the fan or AC and do that those units shut off immediately. When I try to wiggle the tstat while trying to get the furnace to start again, nothing happens. My guess at this point is that the tstat is bad. It is an Airxcel. Any recommendation on what to replace it with or other suggestions? Thanks Jd
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09-03-2019, 04:37 PM #6
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ok, bit of an update... The furnace would not run at all, I just checked the tstat, curious at what was causing it to go out and it was the fuse in back. The barely functional holder for it was letting it move around. Now its not a problem for the moment. The furnace still will not start via the thermostat. it will if I take the fuse out of the panel and put it back in or unplug/plug in the shore power. Otherwise it won't start. Even with the propane off and if I pull and reinsert the fuse the furnace will come on and run, then shut off but the tstat seems to have no effect on the furnace.
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09-07-2019, 04:29 PM #7
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I think I found the problem, but not sure how it is corrected. I have attached some photos to help with what I am about to describe.
1. The blue and blue/white wires from the furnace connect to a green and black set of wires. Blue to green, B/W to black.
2. the green and black wires go up into the AC and are joined together there.
3. In the AC the green wire from the thermostat is just dangling in the open, not connected to anything.
4. The thermostat with its wires. (Of course none are color coded like any of the legends I could find). The green one is the furnace wire, and it is the one seen dangling in the AC.
I ran continuity test on all the wires in question and as far as I can tell they are all straight runs with no hidden branches.
Now it seems to me that the green and black wire should not be connected together. Shouldn't one run to the green wire dangling in the AC and the other run to a ground to make a complete circuit or am I off base here.
Need some advice as to how this should be wired, as right now the furnace is not attached to the Tstat in any way that I can see.
Thanks..
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09-07-2019, 06:56 PM #8
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I think you need to get the wiring diagram for the furnace. I think it will be helpful. Maybe disconnect the shorted wires and try plugging and unplugging rig to see what happens.
Larry KE4DMG
2022 F-350 KRU SRW LB - Airlift 5000+, ForScan, 37 RDS Aux Tank,
2019 310GK-R - Sailuns; MorRyde IS; Disc Brakes; 20K Reese Goosebox
Search kalakamods for my mods
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09-07-2019, 08:51 PM #9
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So I took the two wires that are put together in the AC and tried the plug in the rig. It did not strart. As soon as I touched the two together it started... I checked the voltage on the 2 wires and the black one which connects to the blue/white wire at the furnace has 12 volts all the time. the green wire is not energized.
I hooked the black wire to the green wire in the AC which goes to the tstat and the furnace seemed to work normally. At least it came on when called for heat, went off when the heat set point was reached, and it would also shut off when the Tstat was turned to off. I have no idea what to do with the green wire that is hooked to the blue wire on the furnace.
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09-08-2019, 09:03 AM #10
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Certainly sounds like it was wired wrong. The Tstat should send 12v to the furnace when it calls for heat. You should go on line and pull the wiring diagram for your model furnace ( it should be in the install/owners manual). The one I found on line shows 3 wires from the furnace: 12v in, gnd, and 1 that is fed 12b from The Tstat.
Larry KE4DMG
2022 F-350 KRU SRW LB - Airlift 5000+, ForScan, 37 RDS Aux Tank,
2019 310GK-R - Sailuns; MorRyde IS; Disc Brakes; 20K Reese Goosebox
Search kalakamods for my mods
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