Dometic Digital Thermostat Replacement

[Jimbee]

Hey All,

My 2013 Passport came equipped with a Dometic Digital Thermostat.I would like to replace it because the on/off temperature swing is much more extreme than I like(7 to 10 degrees) and would also would like a thermostat that is backlit. Somehow this thermostat controls the heat/AC with just 3 wires. Can I install a residential style thermostat in its place?

Many Thanks!

[TomG2]

I had to shield the thermostat in my friend's Airstream, as the airflow was causing the AC to short cycle, as someone else mentioned. I am not a fan (pun intended) of the Dometic thermostat, but when working properly they give good results.

[n7bsn]

smkettner wrote:
More likely the control box. Have read a few issues but not the actual thermostat yet.

Maybe, I wouldn't guess no. But my first thing would be the thermostat. It's the device making the call to turn the heat/cool on/off.

[time2roll]

More likely the control box. Have read a few issues but not the actual thermostat yet.

[Jimbee]

Thanks again for the feed back.
I guess I'll switch out the thermostat and hope for a better performing unit. Sure would be nice to upgrade at this time if there were any other options!

[n7bsn]

Jimbee wrote:
That's the thermostat. Anybody know of a "3wire" digital thermostat that is compatible with this type of control box?

There really isn't going to be much. Unlike more conventional Thermostats this ones "talks" to the control via signals on the third wire.
Conventional ones just switch power to the function, which is why they require so many wires.
My understanding of how this one works, all those "other" wires go to the controller, where their normal functions are run.

I'm certainly in the "something is wrong" camp. That kind of swing, with this type of controller, suggests either the thermostat or the controller it is talking to, has a problem.

[n7bsn]

hddecker wrote:


Do you have you fan set to auto.

How close is the t-stat to a heat register. The genius that designed our camper decided to put a heat register in the hallway right below the stat. Furnace comes on, blows hot air at the stat it shuts off, the ends of the TT were always cooler than was comfortable. I blocked off the register and now the heat cycles as it should.

Try looking around this site if someone has done the mod you may find it here.

http://www.modmyrv.com/2008/07/14/rv-digital-thermostat

Did you look at the type of thermostat he showed? Unlike conventional RV thermo's there is NO Auto/On (fan) switch, that function is buried in the options.

The conversions you (and others) have posted about using a 6 wire system don't work with a three-wire system.

[hddecker]

Jimbee wrote:
Thanks for the replies!
I tried reprograming the thermostat to the 1 degree differential, but it seemed like the thermostat couldn't make up its mind whether to call for heat/AC or not. It kept making an on/off clicking noise from what I assume is a relay switch in the AC unit where the control box is; like the thermostat wouldn't fully commit to a function. I was afraid it would eventually damage whatever relay it was communicating with.

Do you have you fan set to auto.

How close is the t-stat to a heat register. The genius that designed our camper decided to put a heat register in the hallway right below the stat. Furnace comes on, blows hot air at the stat it shuts off, the ends of the TT were always cooler than was comfortable. I blocked off the register and now the heat cycles as it should.

Try looking around this site if someone has done the mod you may find it here.

http://www.modmyrv.com/2008/07/14/rv-digital-thermostat

[time2roll]

I think something is wrong in the ceiling box and probably needs replaced.
Mine does click and either heat or air starts running without hesitation.
Mostly plug and play replacement. However I don't know how to make a positive diagnosis.

You might ask the moderator to move this to "tech issues" as there are a couple trained people that hang out there.

[Jimbee]

Thanks for the replies!
I tried reprograming the thermostat to the 1 degree differential, but it seemed like the thermostat couldn't make up its mind whether to call for heat/AC or not. It kept making an on/off clicking noise from what I assume is a relay switch in the AC unit where the control box is; like the thermostat wouldn't fully commit to a function. I was afraid it would eventually damage whatever relay it was communicating with.

[time2roll]

There is a setting to adjust the furnace temperature swing to be either 1 degree or 2 degrees.

Thermostat manual Furnace swing adjustment page 9

How are you measuring the temperature swing?

[Jimbee]

That's the thermostat. Anybody know of a "3wire" digital thermostat that is compatible with this type of control box?

[time2roll]

This one?



No you cannot change to a home unit. The control box in the ceiling is not compatible.

The three wires are 12v+, 12v-, and a signal wire.

7 to 10 degree swing seems like something is wrong. Mine holds things pretty steady.

[ScottG]

Yes and for the very best results, get one that is energy star rated. The next best is a Hunter T-stat but it is a distant second to the ES model.
You will however have to add a switch for the low/high AC fan function.