Help before I freeze!

mruther · 12-20-2022, 09:07 PM

Hello, everyone! This is only my second post here. I try my best to look things up online but not had the best luck with my particular problem. After fighting for the last few weeks with my furnace I finally got it running. But now it won't shut off. Today was the first day I had it on for very long and it will just continue to heat. Complicated situation but I have my camper parked at my parent's farm and I work from home. My work office is inside their house. When I took a break from work to come check the furnace my other temperature gauge said it was over 90 degrees in here. I tried turning the tstat off but that didn't work either. The only thing that turns off the furnace besides cutting power is turning off the propane. We are supposed to get single digit and negative temps along with snow the next couple of days and I am trying to figure out if I need a new thermostat or how to test it. My furnace was just at a shop to get tested and I replaced the sail switch in it. There are only a couple mobile techs in my area and because of where I live it is almost $200 just to have them come look at it. Trying to troubleshoot and maybe fix it myself if I can.

My camper is a 2004 Keystone Sprinter 5th Wheel. I have a Suburban SF-30F furnace with a digital Dometic thermostat, an image of the kind I have is attached. Anyone else had this issue?

Thanks in advance!!

CedarCreekWoody · 12-21-2022, 03:46 AM

I'm no help to you but it might help others assist you if you describe what you did while "fighting it".

JBM3M · 12-21-2022, 05:47 AM

use the "auto" setting and that will fix it

wiredgeorge · 12-21-2022, 06:16 AM

Quote:

Originally Posted by JBM3M

use the "auto" setting and that will fix it

Not sure that would help. Auto just runs the fan only when the heat or A/C are kicked on. If temps are getting up to 90F in the camper, the heater is misbehaving or the thermostat. The thermostat should regulate the temp to whatever it is set to and the fan will be running regardless of whether the temp gets to 90F or not. The thermostat doesn't appear to be talking to the furnace.

First thing I would do is wiggle the wires under the A/C that come from the thermostat. Next step would to hire a bona fide RV tech to fix the issue. OP might also want to invest in a small electric heater if connected to shore power and not rely on the camper's furnace which is likely burning through a bunch of propane.

ChuckS · 12-21-2022, 06:45 AM

The original thermostat was the older style bi-metallic one and someone upgraded to the SZ LCD thermostat..

Ive attached a pic showing you how that thermostat is wired. Either the thermostat is not sending the signal to the junction box on the roof to tell the furnace to shut down or the junction box has an issue.

This should be very easy to resolve provided you have some basic electrical skills

**sourdough** · 12-21-2022, 07:30 AM

Someone has replaced the original thermostat with a Dometic CT thermostat. They are prone to problems due to their terrible design - I went through 4 of them on my last trailer before moving to a MicroAir. You might try removing the cover and the little foam inserts under there and just use your fingers on the controls on the bottom portion. You can touch them just as you would touch the buttons on the cover and it will change the functions.

The above recommendation is under the assumption you have all the controls set right; for your situation I would have it set to heat, auto and the temp you want. Monitor what the space heaters are doing (if you are using them) as they will affect how/when the furnace comes on and operates. By doing the above with the thermostat you should be able to see if that is the issue pretty quickly. With as much trouble as they cause I would not be surprised if that wasn't it - particularly since the furnace has been checked out. If you find it is the thermostat call Dometic and tell them. They sent me one or 2 new ones free because they know those things are junk. A new one won't help you in the here and now but maybe using it like I suggested will get you through.

mruther · 12-21-2022, 08:04 AM

Thank you everyone! The settings are correct. The thermostat was replaced when I had a new AC installed a little over a year ago. Things had been working fine until now. The entire issue with the furnace started with my mice invasion. Since having to move back to the farm and off of concrete I have had some issues with mice. I have finally gotten rid of them but a mouse getting into my squirrel cage is what started problems. I just had to change the sail switch to get the furnace working again. The reason it went to the shop was because I had hooked it back up and it still didn't come on. Turns out I had to switch the blue wires. And now it will heat up non-stop. Literally. I have to turn the propane off to shut the furnace down. Even turning the thermostat off did not help. I just didn't know if I needed to replaced the thermostat or if it might be a part in the furnace itself. Maybe there isn't a way to tell. I am not likely to get a tech out to look before the single digit temps hit.

**chuckster57** · 12-21-2022, 10:11 AM

The blue wires are the thermostat “signal” wires. If you have 12VDC on both leads your furnace will not shut off. Once set temp is reached, the “continuity” is broken and the control board will set the furnace into cool down mode.

I would check both of them for voltage and go from there.

mruther · 12-21-2022, 11:50 AM

I checked and only power at one blue wire. I tested a couple other things too. I had the furnace running and the thermostat off and I unplugged one of the wires in the climate control. It kept running so not the climate control. Then I unhooked one of the blue wires and it stopped running. It stopped heating and then did its cool cycle before turning off. The tech I talked to talked about maybe mice eating the insulation on my wiring and I need to make the two blue wires one essentially and change a couple things in the thermostat wiring in the climate control. Basically, make it so the furnace gets power from the climate control instead. What do you guys think? I have never done so I would be going off of telephone instructions and I am loathe to do so.

**chuckster57** · 12-21-2022, 12:17 PM

If memory serves me the blue wire gets 12V from the control board to the thermostat and then back to the board.

You could install an analog heat only thermostat to get you through.

https://www.etrailer.com/Accessories...ontent=General

mruther · 12-21-2022, 12:19 PM

My sister is going to pick up one on her way home tonight. Though I am not entirely sure how to wire it to the furnace yet. I did check and I have 9.5V going to one of the blue wires.

**chuckster57** · 12-21-2022, 12:23 PM

That thermostat should have instructions. It’s simple as the two posts will be easy to identify and I don’t believe it matters which one goes which post.

adeakins · 12-29-2022, 02:32 PM

Been there, feel your frustration. In my opinion and that of several RV pros with whom I’ve shared my similar albeit not exactly identical experience, these Dometic thermostats are unreliable and, worse, can go totally insane with no warning. Mine, too, appeared to not be talking to my furnace, my heat pump nor my AC. In fact, it wasn’t even talking to me. Most of this was without anyone touching it. Who or whatever it was talking to had to be in some other universe far, far away. It would spin the temperature spectrum, flip from mode to mode, again, without my participation, jump back and forth from centigrade to Fahrenheit and turn-on the furnace and the heat pump at the same time … which isn’t supposed to be possible. But, my wife and I saw it do just that. Anyway, aside from the paranormal, I was at a loss. So, I called my favorite RV mobile tech and he responded with; “… get a new thermostat and call me in the morning.” Well, I had to order one because none of the local parts shops carried them in stock. I did, it came, the tech installed it and all appears to be well. And, best of all; my RV is not haunted … but I’m not sure about cursed.

wiredgeorge · 12-29-2022, 03:06 PM

For Chuck or anyone who can answer... is there a reason that an older analog thermostat could not be used. I have it controlling a newer Dometic A/C and the original heater. I think a simpler thermostat might solve a lot of the problems with newer Dometic thermostats. Analog is sometimes good.

**chuckster57** · 12-30-2022, 04:48 AM

Quote:

Originally Posted by wiredgeorge

For Chuck or anyone who can answer... is there a reason that an older analog thermostat could not be used. I have it controlling a newer Dometic A/C and the original heater. I think a simpler thermostat might solve a lot of the problems with newer Dometic thermostats. Analog is sometimes good.

It depends on what is installed at the roof unit. We just replaced a low profile unit yesterday, it had a heat strip and that thermostat. Since it was in the bedroom it didn’t control the furnace. New roof unit has heat pump, and since all the logic controls are on a board “up stairs” the analog thermostat won’t work. Actually had to get the one shown with heat pump option. Old thermostat was 5 wire new one is 3.

Max23 · 12-30-2022, 07:41 AM

Quote:

Originally Posted by chuckster57

It depends on what is installed at the roof unit. We just replaced a low profile unit yesterday, it had a heat strip and that thermostat. Since it was in the bedroom it didn’t control the furnace. New roof unit has heat pump, and since all the logic controls are on a board “up stairs” the analog thermostat won’t work. Actually had to get the one shown with heat pump option. Old thermostat was 5 wire new one is 3.

I'm assuming thats only if you have a "heat pump"????? Sorry, reading through just learning what I can do when mine "probably" craps out.

**chuckster57** · 12-30-2022, 08:07 AM

Quote:

Originally Posted by Max23

I'm assuming thats only if you have a "heat pump"????? Sorry, reading through just learning what I can do when mine "probably" craps out.

Lots of different variables, I would just wait.

wiredgeorge · 12-30-2022, 09:08 AM

Quote:

Originally Posted by chuckster57

Lots of different variables, I would just wait.

I installed a Dometic Brisk II A/C a couple years ago with no heat pump and my original 2002 Duo Therm thermostat connected right up as I recall. It was long enough ago that I can't remember what was done but there was no fuss or drama as I recall. I had one of those more modern round Dometic thermostats in a Sunnybrook bumper pull I owned a number of years ago and it had a mind of its own.

apachewolf · 01-04-2023, 01:21 PM

Far too often we see members here looking for thermostats for their camper, be it Motorhomes, 5th wheels or travel trailers. I have a 2015 Keystone Laredo 240MK that came with a “mechanical’ thermostat. Not very accurate. One problem here is that most thermostats run on 20vac because that is what in house furnaces and AC units uses to control the units. I choose a unit from Honeywell RTH 221B1021 which runs on 2 AAA batteries. They last for a year or more. The unit is programmable with 4 settings a day for the whole week. It runs both the AC and the furnace. Has a LCD display but unfortunately it is not lighted meaning that you may have to use a flash light to see where you are at. However because it runs on batteries you can take it to the dining table and program it there. It has at the bottom left a switch that controls Heat-Off-AC and to the right a switch for the fan On – Auto. I am not sure of the price at this moment but I paid about $ 15.00 for my unit back in 2015 so it is probably more today but still way cheaper than some I have seen suggested here. I got mine at Wally World but I have seen them at other stores. Installation is super easy. Just move the wires from the old to the new unit.

Happy camping.

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