Dometic A/C - Thermostat options?

[LifeInsideJack]

We have the typical rooftop Dometic a/c unit on our motor home. The controls for this are right on the part that is on the ceiling. Basically fan/cooling control on the left and a temperature control knob on the right that operates at either Too Cold or Not Cold with little in between.

Is there a thermostat option for this thing? Has anyone installed such a thing? Did it work? Can I operate it from my phone?

At times we need to leave this running when we run out and this unit just chugs away and when we come back the coach is cold and the cat is very enthusiastic about making sure we know she is unhappy.

[j-d]

You have two control knobs, right? One is the Temperature Knob. The other is a Switch with say Off, Low Fan, High Fan, Low Cool, High Cool, right?

I'm just guessing here, but couldn't you put a relay in place of the Temp Knob then a wall thermostat with appropriate control voltage for the Relay? The A/C Fan would run (should always be on HIGH when using Cooling!) full time, then the Compressor would cycle based on the new wall thermostat.

Now that I've said that, wondering if I could do that on our Coleman Mach...?

[Chris_Bryant]

It sounds like the cap tube for the thermostat is not positioned correctly. Remove the filter, and you should see the silver tube coming out of the control box- it needs to be positioned in the return air stream- IIRC, there is a small holder with a plastic grommet it needs to be in.
I have seen the tube stuck in the coils, which doesn't work.

That thermostat should be fairly adjustable and accurate, once you find the right position for it.

[time2roll]

I think you can avoid 60 degrees by adjusting the existing thermostat. When the wall thermometer hits 74 (or your choice) simply move the thermostat very slowly toward warmer until the compressor turns off. Mark that with a pencil.

OK it might not hold the exact temperature but should keep within 3 to 5 degrees plus or minus. Adjust a bit depending on conditions. There is no throttle on these air conditioners they just cycle on and off the compressor. Max cool setting does not cool the RV any faster.

That is the temporary fix to a temporary problem.

[LifeInsideJack]

Kayteg1 wrote:
Starting the topic you said you have temperature control on your AC, now you are saying you have no thermostat.
How about a picture?

The temp control is the knob on the piece located on the ceiling. The thermostat in the hall is for the heat only. So what is controlling (poorly) the temp on the A/C is this twist knob that is labelled "warmer - colder".

The A/C unit is turned on manually and the knob on the right turn up or down but it is so stinkin' hot here we just keep it turned to "colder" all the time.

Adding a thermostat is dodgy because that would only be able to turn on or turn off the A/C unit for us. So the A/C is in the Max A/C position on the left knob (thus "on") and the right knob is in the "colder" position all the time. The relay between the thermostat and the breaker for the A/C would then turn the power to the A/C on and off according to the temperature setting on the thermostat.

This is the solution that I have found that does NOT require a new A/C unit and a bunch of wiring.

However, I'm not sure of this as being any real type of solution. What are we trying to avoid? We have returned to the coach after being away for several hours, well after dark, and the cat is yelling at us because it's about 60* in the coach. She's a desert cat, she loves the heat. It's so silly of a problem we leave our cat's heated bed on so she has a warm place to hide from the brisk interior of the coach.

This is the part that I don't want to get back to my girlfriend. The cat is 18 ... this is a short term problem in reality. Not nice to say, but truthful.

I was looking for a simple way to turn on and off the A/C but all of this points to a circus solution that I'm not sure would be good for the overall health of the A/C unit in place.

I hope this helps make clear the situation we have going on in here.

[Kayteg1]

I think the AC-mounted thermostats are 120V, so wall thermostat is not going to be plug & play ?
Than my AC thermostat does decent job, so unless going for Wi-Fi digital thermostat, I don't think I would gain much by installing wall thermostat.
Also have not seen wall thermostat that would give me 3 fan speeds, like my AC has.

[Chris_Bryant]

I would just buy the control kit- plug and play, 3 wire t-stat.

[Kayteg1]

Starting the topic you said you have temperature control on your AC, now you are saying you have no thermostat.
How about a picture?

[LifeInsideJack]

To be clear ... there is no thermostat on the A/C at this time.

This post is to figure out how to adapt a thermostat onto this unit.

For this I have found the relay ($10) and a thermostat that has a timer to prevent the A/C from starting up too soon and thus hurting the compressor.

As for digital or analog ... not sure I care that much. I'll probably install a digital that will operate the relay as well as control to heater.

The current "to solve" now is how to get the wires from the relay to the current thermostat (for heater) location. Being that the coach is old and I'm not interested in making a Very Big project out of this I'm thinking surface mount conduit along the wall near the ceiling.

My first mistake was buying an older coach that was a "deal" that I'm now upside down on. Fortunately the biggest project to date has been the solar kit that is stupid large but this is my girlfriends skill level as she is an electrician on large solar farms. We bartered for the equipment but that equipment is worth more than the coach.

I'm nearly certain buying this was a good idea .... but that's a thin argument.

Thank you all for your help and input.

[Chris_Bryant]

If your thermostat looks like this:
then you can adapt standard thermostat to use.

[time2roll]

shastagary wrote:
looks like its possible i don't know how hard it is to install dometic thermostat install kit

If you are going to adapt the single zone at least get the new one listed as Capacitive Touch.

http://www.rvpartscountry.com/Upgraded-Dometic-Single-Zone-RV-Air-Conditioner-Thermostat-1.html

This link is for the thermostat only. You will need the relay box also for about $80 total. Not programmable but does have automatic high/low fan.

To make a hunter or other thermostat work with a Dometic relay box you need an old box that used the old analog thermostat. The new digital control box will not work with home style thermostats.

[Kayteg1]

LifeInsideJack wrote:
We have the typical rooftop Dometic a/c unit on our motor home. The controls for this are right on the part that is on the ceiling. Basically fan/cooling control on the left and a temperature control knob on the right that operates at either Too Cold or Not Cold with little in between.

You described your thermostat.
Mechanical thermostats usually have big difference between cutting in and out, so this is what you are experiencing.
Mine, sounds like identical gives me 5 degrees differences. Wall-mounted mechanical thermostat will have the same issue, although hopefully with slight improvement.
Digital thermostat will give you 2 degrees difference what might be better for you, although I found it sometimes annoying when AC comes in/out every 90 seconds.

[LifeInsideJack]

Wow. Very helpful and very quick.

With this information I was able to locate a suitable relay to control the On/Off function between the A/C and the breaker. This way the A/C is "on" all the time and the thermostat then turns on and off the A/C as the temperature setting dictate.

I was able to locate a Hunter brand t-stat that has a time delay function to avoid turning on and off the A/C too quickly and thus damaging the unit. Fortunately for me my girlfriend is an electrician and will quite easily over-engineer this simple solution into something with copious safety features.

Thank you for your push in the right direction.

All the best,

Montana

[shastagary]

looks like its possible i don't know how hard it is to install dometic thermostat install kit

[dougrainer]

You have to change out the ceiling mount and add a control box and a wall tstat. Dometic used to have a IR tstat remote, but you still had to change out the upper ceiling unit and add the control box. While Dometic has/had the IR remote I have never seen one. I have worked on thousands of Dometics over the years. I know of none that will work with a Cell phone. But, there may be aftermarket adapter kits to do that. Doug

https://www.amazon.com/Dometic-Conditioner-Single-Thermostat-Control/dp/B00C9OEYOI/ref=pd_lpo_vtph_2...