Furnace vs. Themostat Problem

[timolson5367]

I have a 2008 FR Sierra 5th wheel with a SF-30 Suburban furnace and a Dometic thermostat. My problem is the furnace will not shut off when the temperature inside the 5th wheel trailer reaches the set temperature. The furnace will eventually shut down when the temperature is about 10 degrees warmer that the set temperature. When it does turn off the furnace will not turn back on when the temperature inside the trailer drops. I have to take the temperature setting lever on the thermostat all the way to the bottom and then raise it up to restart the furnace.

This issue started several months ago while out hunting and after getting home the furnace would not even light. I could hear the blower (which was strong) running and I could hear the igniter sparking but the furnace would not start. I checked the limit switch and that was good. So I took in to the local RV dealership and they replaced the circuit board in the furnace, cleaned it out and said it was working per design. After taking it home I found that the furnace was having the same issues as stated above except it now fired up. So I took it back and they said they could not find a problem except it would take 30 seconds for the furnace to relit when the temperature dropped low enough. They replaced the thermostat (at no charge) and said it was continuing to have the same restart problems but they could find nothing else wrong.

Well, after getting it home the second time I again and having the same problem with the furnace not restarting when the temperature drops. Does any one have a suggestion on what my next step would be?

[Witch Doctor]

What stat did they put on? I would go to Home Depot and buy a new stat. Sounds like it has been the stat the whole time. Check some threads on them they even show how people wired them in with the high low fan speed with an added switch. I never use high to much noise for me so I would just drop that wire out. Get a digital read out and a plus and minus 1 degree. I think they cost about $30.00 bucks.

[rockfordroo]

I had a similar problem with my brand new Roo19. I replaced the POS Suburban mechanical Tstat with a non-programmable Honeywell RTH111, like this:

Honeywell RTH111B1016/A Digital Non-Programmable Thermostat-Price Machine

Here's the programmable version:
Honeywell RTH221B1021/A 1 Week Programmable Thermostat - Amazon.com

Of course, there are many others available.

No problems since. It keeps the temp closer to the setpoint, and it works every time. Plus gives you an real temperature readout, not some mechanical thing you can hardly read.

[timolson5367]

Thank you. They did put back in another dometic stat very similar to the original one installed. Both stats were digital control not metchanical. It won't hurt to try a digital readout stat.

Originally Posted by gljurczyk

What stat did they put on? I would go to Home Depot and buy a new stat. Sounds like it has been the stat the whole time. Check some threads on them they even show how people wired them in with the high low fan speed with an added switch. I never use high to much noise for me so I would just drop that wire out. Get a digital read out and a plus and minus 1 degree. I think they cost about $30.00 bucks.

[timolson5367]

I picked up a new Honeywell thermostat model RTH111B/1024A. This model looks identical to the Honeywell 1116A model. The wiring has me confused however. My old dometic wiring is as follows:
+7.5 = Red
Cool = Yellow
Furnace = White
Hi Fan = Blue
Fan = Brown
Ground = Green

On the Honeywell stat I have: B, O, G, Y, W, Not Used, R and RC (the
R and RC are jumpered together.

Can anyone tell me the correct wiring order or should I call Honeywell directly. Thank you

[Witch Doctor]

This might help you. The red to r/rc
the yellow to y
the white to w
the blue or brown to g depending what speed you want
Do not hook the the green.......Try that it should work. you will only get 1 fan speed without adding a switch. I think that should work I do not know the stat. there shouldn't be a ground on that new stat. If you want to hook it up just go to the frame of the ac unit in the R/A area. your new stat should show you what the b,o are used for. they will use the same sub base for a bunch of different apps.