Blank Thermostat

[Happycampper]

Hello everyone,

I have a 2013 38GK.

I tried turning on the main A/C for the first time this year and as I was adjusting the temperature on the thermostat I heard a little click from the thermostat then it went blank. I checked the fuse in the thermostat and it's good. I turned all the breakers on and off and checked for power and loose connections at the breakers, everything is good. I checked all the 12v fuses and the are all good. I pulled the thermostat and all the connections are fine. Checked for power and getting 2v.

The thermostat is completely blank so no A/C, no heat pump and no furnace.

The a/c in the bedroom is working fine.

There has to be a transformer somewhere for suppling the t-stat with low voltage anyone know from where? Since it's going to both the A/C and furnace I'm not sure which one to check.

I would really like to hear what you seasoned experts think the problem is before I proceed.

Any help would be appreciated.

[Jim & Mary]

My thermostat documentation shows primary voltage is 12VDC so it gets it straight from battery voltage (through a fuse) If you are really getting 2V only that's a problem you have to find the reason for. When we had trouble with awning power, I saw no blown fuse indicators in the power panel, but turns out the fuse was blown.

[Happycampper]

I guess getting 12v to the t-stat directly makes sense. I am used to residential HVAC where the t-stat gets power from the equipment. I am getting 12v after all the fuses in the panel. Could there be a hidden fuse elsewhere? I think that if I could figure out why I'm not getting the 12v it will solve my problem. Thanks.

[Jim & Mary]

I have two suggestions
1. There may be an internal thermostat fuse........that bears checking
2. I would make sure all wiring connections for the 12V circuits in the right side of the power panel are tight. That includes the negative side of the 12V circuit. You could have a wiring break in the neg 12V side as well. Take off the big switch panel (where the slide switches, pump switches, etc. are) and see if you can see loose wires in wire nuts, etc. I know it's a PITA, but most of these problems are.

[Happycampper]

Quick update... I removed the red (power) wire from the t-stat and checked for voltage and I am in fact getting 12v. With the red wire connected to the t-stat I am getting 2v. I am now suspecting a faulty t-stat. The fuse in the t-stat is good.

[r time soon]

Not doubting that the fuse tested good, but did you remove it from the thermostat and check for continuity? I recently had issues with our 2012 36RL. Thermostat had blank screen. Fuse was blown. Installed another fuse and it blew almost immediately. Ended up I had issues up on the air conditioner on the roof that was causing the fuse to blow.

[Happycampper]

Yes I remove the fuse and tested it. It is good unfortunately. Does anyone know what size (how many amps) this fuse should be?

[r time soon]

For my Coleman Mach or Airxcel the fuses are 2 amp.


We have 2 model 48254B879 A/C's


Main thermostat is for cool and heat, controlling the furnace as we don't have heat pumps.


Bedroom thermostat is cool only.

[XCMARK]

I had a similar issue with my tStat , I found the contacts on the slide switches must have got some corrosion in the slide switches , guessing the contacts have grease or they are silver plated . the grease gets hard over time and the contact cant move the grease to get to metal or the silver tarnished. End result I sprayed silicone lube in the switch and worked it back and forth fast for about 20 seconds each . becarful to not get the spray on wood or the plastic outside cover it may stain it. Problem solved , maybe it was good luck but your maybe the same fix. I gave it a good 2 second blast of spray on each side of the switch body ( both switches)

[Happycampper]

I will certainly give that a try, Thanks

[Jim & Mary]

My literature says 2A fast acting (not time delay).

[Happycampper]

That's what is there. I was thinking if the previous owner oversized it that might be what damaged the stat but it is correct. I will try cleaning the contacts on the switches but there is no display at all so I will be surprised if it works. Thanks.

[XCMARK]

Originally Posted by Happycampper

That's what is there. I was thinking if the previous owner oversized it that might be what damaged the stat but it is correct. I will try cleaning the contacts on the switches but there is no display at all so I will be surprised if it works. Thanks.

I cleaned mine back in march , I cant honestly say the screen was blank but I could not get the heat or the heat pump to turn on before my ride out to Morride. That was my cure luckly , those Tstats are not cheap.

[Happycampper]

New update.... I am really confused now. I took the t-stat off the wall and connected the red wire +12v and the blue wire -12v to my booster pack and voila the t-stat display lights up just fine. I checked for power on the coach side of these wires and I get 12.4 volts but if I connect just these 2 wires back to the stat and no others just like I did to the booster pack then the stat should light up right? Wrong! I get nothing. How is it possible that the 12v booster pack lights the stat but the 12v wires at the coach that have 12.4 v does not????
I traced back the power wire (red) for the t-stat and they go to the furnace.
I'm thinking that I need to test the t-stat right at the furnace to eliminate any possibility that the thermostat wire is pinched somewhere between the furnace and the wire outlet in the hallway and is able to supply 12v but too damaged to carry any load? I don't know. Maybe I should also jumper red and white right at the furnace to see if it fires up.

I did try jumping White and Red from the hallway to start the furnace and got nothing. I tried jumping red and grey and yellow to start the A/C and again I got nothing.

I'm hoping that someone has another suggestion before I do this as I would have to remove part of the carpeted wall in the basement to get access to the furnace. I can almost reach through the little access door but no quite enough to do the wiring.

Can anyone make sense of this?

[brenda.taylor59@gmail.com]

We had a similar situation. We updated our system and everything has been fine. You have to download to a flash drive and insert in the bottom of the control panel. Hope this helps.

[Elliott & Vicky]

I'm on my 3rd Tstat on my 2013. Once it just went weird and would work sometimes and sometimes not. Rather than screw around with it, I just replaced it. The slide switch to select between heat and AC failed on the other one. Contact cleaner did nothing for it.

[Flying Dogg]

On our 2014 36RL the thermostat is powered from the furnace control board. There would be 12v when tested static but would drop to ~0v when a load was present. The relay on the furnace control board was defective. Replaced the board and all is well.

[ted 95]

you have reversed the + and - when you were testing the wires???

[Happycampper]

Problem finally resolved. Thanks to everyone with the help with this issue. I finally took some time to work on this and found that there is on on/off switch inside the furnace behind the outside access cover. This switch was green with corrosion so I decided to bypass it and found that one of the spade connectors has completely corroded away. Once this problem was repaired the t-stat worked fine for the a/c and heat pump but would blow a fuse in the panel when I tried the furnace. Turns out the blower on the furnace was seized. After carefully turning the blower by hand and spraying WD40 I managed to free it up and now everything is working perfectly. This unit is a 2013 that was very seldom used by previous owners and I don't think this furnace has ever been fired up. I guess that's why it seized up. I may have to eventually replace the blower but it's working for now.
Thanks again.