Problem with RV Comfort.HP thermostat for Coleman Mach Heater & A/C

[Dot&Sam]

Greetings. We are the proud owners of a 2016 Jayco Greyhawk 31 FS motorhome. All is well except for an annoying problem with the Coleman Aircell heating unit. It seems to be a problem with the RV Comfort.HP thermostat. We have the choice between elec. and gas heat. The electric works fine. When we use the gas heat, which we do when "off the grid", then we set the thermostat for about 63 degrees. It always wakes us up at night as it has automatically switched back to 72 degrees and is running constantly. We can reset it for 63 but then the same thing happens later.

Is this a faulty thermostat that needs to be replaced or can I correct this on the existing one? If I can fix, please describe how.

Thanks,
Sam

[Franklin6140]

Did you find a solution, mine is doing the same thing. I was wondering if we could use a different thermostat since another issue we have is that it's very hard to see.

[Grumpy]

Originally Posted by Franklin6140

Did you find a solution, mine is doing the same thing. I was wondering if we could use a different thermostat since another issue we have is that it's very hard to see.

When it defaults back to 72 it usually means it lost power. So if the battery voltage drops enough when the furnace first kicks on that could cause the issue. Just something to check.

[madmaxmutt]

The only way mine was fixed was to run new wires to power it. The circuit it was on was affected by the furnace lighting.

[memphis02]

I recently contacted the manufacturer about this and they said (insisted) the same thing, that there was a voltage drop. I'm certain there is no way for this to happen unless there is a problem with the thermostat or wiring. I plan to put my datalogger on this to see what I can figure out, next time I run the furnace.

[madmaxmutt]

Originally Posted by memphis02

I recently contacted the manufacturer about this and they said (insisted) the same thing, that there was a voltage drop. I'm certain there is no way for this to happen unless there is a problem with the thermostat or wiring. I plan to put my datalogger on this to see what I can figure out, next time I run the furnace.

It is exactly that. The voltage drops when the furnace ignites, because of the way Jayco wired it. I tried two other digital thermostats. Same symptoms.

[Franklin6140]

Originally Posted by madmaxmutt

The only way mine was fixed was to run new wires to power it. The circuit it was on was affected by the furnace lighting.

So you ran new wires to the t-stat.what about the wiring to the furnace that seems to be the root problem should I be checking that

[madmaxmutt]

Originally Posted by Franklin6140

So you ran new wires to the t-stat.what about the wiring to the furnace that seems to be the root problem should I be checking that

They only checked the ground and power wires for my furnace. They ran a new power and ground for the thermostat. It was the no longer tied to the power / ground for the furnace itself.

I would bet if you rigged a temporary 12v light to the current thermostat power and ground it will go out when the furnace lights.

[Franklin6140]

I have noticed some flickering lights when my furnace kicks on

[memphis02]

I have discussed this with my friend who's an electrical engineer. We're kicking around the possibility that the furnace motor is inducing noise on the thermostat power line and it's making it grumpy, to the point that it resets. I'm going to try adding in some decoupling capacitors at the thermostat. If this works, I'll share my info. If it doesn't work, we'll know, with reasonable certainty, that the problem is that the power is dropping.

[MontanaBBQ]

We had the same problem on our ‘16 31FS when it was new. Jayco had a known fix for this problem. They used to have a relay kit that could be installed in the power wiring to the furnace. Back in 2017, my local dealer replaced our wall t-stat under warranty. It didn’t solve the problem.

I referred them to this post:

https://www.jaycoowners.com/forums/f5/rvcomfort-hp-thermostat-problem-27437.html

They contacted Jayco, ordered and installed the relay kit, problem solved ever since.

-Doug

[LI-Camper]

The position of the slider on the thermostat was difficult to see. I used a bright yellow Post-It to solve this problem. I cut a little square out of the Post-It where the adhesive is. The size of the square is the same size as the “slider” . Before I cut the square out I drew a vertical line with a regular pen on the square. I stuck the small square on the thermostat slider and now I can easily read the position of the slider (ie, electric heat, gas heat, off, etc.). This has remained on the thermostat for about 3 years so far.