Can I Use the DMC79FR Thermostat to Upgrade My Duo-Therm Quick Cool AC to Digital?  

Question:

Expert Reply:

Hello Larry,

I get why you were looking at the # DMC79FR, but that one isn’t going to do the job for your setup. It’s just a thermostat replacement for systems that already have a digital control board. Since your Duo-Therm Quick Cool is still running the older analog style controls, there’s nothing there for that thermostat to talk to, so it wouldn’t actually run your A/C or furnace.

What you’ll need instead is the full conversion kit, part # DMC83ZR. That gives you both the digital thermostat and the new control board that installs up in the ceiling assembly. That control board is really the key, because it replaces the old analog setup and lets the new thermostat control both your A/C and your propane furnace from one spot, just like you’re used to now.

The install is pretty straightforward if you’re comfortable with basic wiring. You’ll pull down the inside A/C cover to get to the control box, remove the old analog board, and swap in the new one. As you’re doing that, you’ll move your existing wires over to the new board, including tying your furnace wires into the correct terminals so everything still runs through the same thermostat. Then you’ll run the included harness to your wall, mount the new thermostat, and plug it in. Once you power it back up, it should recognize the system and be ready to go.

Where people usually run into trouble is either leaving part of the old analog board in place or getting the furnace wires on the wrong terminals, so it’s worth taking a second to double-check those as you go.

Once it’s in, it’s a nice upgrade and a lot easier to live with than the old analog controls.

What kind of trips are you getting ready for once you’ve got the A/C dialed in?

expert reply by: Kate F

0

Digital Thermostat
(click to enlarge)

Bill R.

5/13/2026

With regards to instructions listed above for full conversion kit, part # DMC83ZR, I'm wondering how people normally get the new wiring harness from the control box over to the wall T-Stat location. Is there a conduit in there? Surely not surface mount?!

Kate F.

5/15/2026

@BillR Great question. Most RVs do not have a separate conduit already run for the thermostat wiring. In setups like this, if the RV originally had a wall thermostat, installers will normally reuse the existing thermostat wire already hidden in the walls or ceiling. If the system originally used ceiling controls instead of a wall thermostat, then a new low-voltage wire usually has to be fished from the new control box to the thermostat location. Most people route it through ceiling cavities, cabinets, ductwork, or alongside existing wiring runs so it stays hidden. Surface mounting is usually only done as a last resort if there’s no good concealed path available.