Replacing Dometic single zone thermostat

[Flyerone]

I want to replace my Dometic LCD single zone thermostat with a programmable thermostat. When I look at the existing Dometic there are only 3 wires connected, labeled +12 Common -12. How can I installed a digital programmable?

 

[Rickhansen]

Hi Tom and Sondra,
You have to remove the Dometic Thermostat, remove the Dometic Digital Interface box, add an analog interface box, and replace the 3 conductor wire with multi-conductor (5 or 6) wire. You can learn more by reading the Heating and Cooling User Guide in the manuals section of this website. It's not a really easy upgrade, but it's do-able. The hard part is sourcing the analog interface, you might be able to get one from Heartland or PPL.

I don't have the analog interface box part number, but I searched on ebay for "Dometic Analog Interface" and found this and this one. There's a good number of sources for the wiring diagram. You'll probably need to add a toggle switch for two speed fan operation. Many folks replace with Hunter thermostat available a Wally World for about $20. I like my programmable Stat, though.

Hope this helps.

 

[Flyerone]

Where is the digital interface box? It has the multi conductor wire already run, they are just using 3 conductors. Which programmable stat are you using?

 

[Rickhansen]

It is normally mounted in the return air plenum of the Air Conditioner. I have 2 Honeywell programmable thermostats, I don't recall the exact model numbers. I got them at Home Depot. By setting the setpoints a degree or two apart, I can operate the two air conditioners somewhat in a lead-lag fashion to improve the temperature and fan noise of the room we're in. The biggest improvement in comfort is that you can set the cycle rate tighter so you don't get big temperature swings.