Replace Dometic CT thermostat with a Programmable one

[ex-egll]

Hi, we have just picked up our 2020 Sabre 37FLH. It has 2 Dometic CT single zone thermostats, one in the bedroom which only controls the bedroom A/C and one in the living area that controls both the furnace and the main A/C. I would like to replace the living room thermostat with a programmable one so that we can set different temperatures throughout the day. Originally I was just going to put a Honeywell or equivalent in, but realised that would not work as the control from the thermostat is digital to a control box, then onto the A/C and furnace. Not having a clue where the control box is I am not sure how to get control of the furnace and A/C.

Dometic have a programmable thermostat, but I believe it would use a different control box, same problem as above, where is the control box.

Next thought is to replace the CT with the Bluetooth version which I think is a direct replacement using the same control box. I know there is an APP to control this unit, but does anyone know whether it would be compatible with Google Home / Google Nest?

Any other ideas would be appreciated.

Barry

[Bama Rambler]

The Dometic CT uses digital communication as you stated, so you can't just replace it with another thermostat as you've found out.

The control box in the A/C. If you remove the grill you'll be able to see it. It's a small metal box in the intake section of the A/C.

Unfortunately the Bluetooth version of the Dometic unit isn't compatible with any of the smart home devices that I know of.

[ex-egll]

Thanks Bama Rambler, I figured the Bluetooth version wouldn't work with Google Home. I'll look for the box in the AC unit. I think I'll try to find a way to install the CCC2 programmable thermostat, if the control box is in the A/C unit it shouldn't be too difficult to switch out for the CCC2 box. That still leaves 2 concerns; is the A/C unit compatible with the CCC2 and how may wires in the control line from the thermostat, I have a feeling it is 4 whereas the current one is 3. Pulling a new wire through may put an end to the plan

Back to research!!

[ex-egll]

A quick update. It seems the stars are aligning. Although the current CT thermostat uses 3 wires, Forest River were kind enough to use 4 conductor wire! The A/C unit is a BRISK 2 so that is compatible with the CCC2 control box, so it seems it shouldn't be too difficult to switch.

Barry

[Bama Rambler]

I'm glad things are working out for you. As you surmised, pulling new thermostat wire is usually the biggest hurdle, because they don't always run them where they're easy to access.

[ex-egll]

Final Update.

Bought the Dometic Programmable Thermostat and Control box. Although there were no instructions with the controller installation was aided by the wiring diagrams on both the old and new controller boxes, together with with some wire labels that were on wires on the A/C unit. The 110v connections were simple (after turning the breaker off), the wiring from the controller to the A/C unit uses the same connector as the previous controller and the 110v in put can be connected using the previous re-usable spring connectors. The furnace wires and 12v supply need to be spliced into the new six way connector (supplied) and the defrost sensor is plug and play.

Once that was done all that was left was to connect up the thermostat, for this i bought a small telephone cable with RJ11 connectors on the end. I cut off each end of the cable about 8" back from the connector and stripped the ends. I also cut back the outer jacket of the 4 wire thermostat cable that runs in the wall, once this is done you will find there really are 4 wires in the cable, only 3 were used and the fourth was cut back. Now comes the only tricky part, you can splice any colour wire from the phone cable to the existing cable BUT DO NOT do this at the A/C end. If you were to look at the two RJ11 connectors (look at the flat side it is easier) you will notice that the wires are reversed. The left most wire on one is the right most wire on the other, the rest are also reversed. This means that you have to switch the wires around at the A/C end such that the wire from the thermostat that connects to the left had side there has to terminate at the left hand pin at the A/C end. Once that is done, checked and double checked switch the breaker on and the thermostat should come to life. Read the thermos stat instruction book and make sure to INIT the thermostat, I didn't and nearly suffered a hear attack as a result, I got an E1 error message. After an INIT all was good.

By shopping around you can get the thermostat and controller for around $200.

I hope this may help someone

Barry

[Otty]

I'm having the same issues. Can you post a picture or link to the unit you used?

[ex-egll]

Hi, the original plan outlined above was modified somewhat!

I ordered the Control Box and Thermostat form RVPartsCountry.com

Removing the old control box and replacing it with the new one went off pretty easily as did installing the new thermostat. It all worked BUT the thermostats programmes left a lot to be desired, if I recall it was limited to 1 on an 1 off time for heat and the same for air so pretty useless for me.

What I did find out in the process though was that for the heating ANY thermostat with a set of relay contacts in it would work, all the heater required for it to fire up was for two wires to be connected together. In the end I used the new thermostat and controller for the A/C as we didn't really need too much in the way of programming for that as we only use the trailer Jan - April in AL, it was more important to have grater control of the heating (this decision was also spurred on by the fact that I found out RVCountryParts will not accept returns on Dometic products!) For the heating I bought a Sensi thermostat that could be far better programmed and could be controlled remotely by the phone. This also allowed me to put the heating thermostat in a much better location than the original. Hope that helps.