Upgrading Dometic Penguin Duo-Therm AC Analog Thermostat to Digital Single Zone Wall Mounted Thermostat.

While cleaning the AC air filters, I noticed 6 unused color coded wires inside the air distribution box. I'm pretty sure I noticed these wires before but really never paid attention to it. I tested the red and black wire for power and was surprised that it has live 12 volt power. I contacted RT but they never gave me a straight answer, so I traced the wires and 5 of the wires terminates into the rear of AV overhead compartment close to where the furnace thermostat is. Obviously it is pre-wiring for the electronic AC thermostat control.

I called Dometic and asked if I can upgrade my current AC (Dometic Penguin Duo-Therm with heat strip option model) to a single zone digital thermostat wall mounted control. I was given the part numbers needed for the upgrade. I was told that I needed the electronic control box (Part # 3313270.000 with Heat Strip option) and I also needed to change the air distribution box in order to mount the electronic control box inside. The air distribution box that came with the RT is a low profile model and does not have enough space for the new electronic control box, but I do like it because of its low profile design.

I bought the Dometic Single Control Kit (Part # 33313270.000) from Ebay. The kit came with the electronic control box, single zone LCD digital thermostat, a manual, and 4 mounting bolts.

The new single zone digital thermostat.


I removed the air distribution box to see if I could squeeze in the electronic control box somewhere. I noticed a gap between the AC divider plate and the AC base pan so I thought the control box would fit there, unfortunately I cannot find any documentation online for the dimension of the electronic control box, just judging from the online pictures I ordered one and hoped that it would fit...and it did!

If your RV is pre-wired for the electronic thermostat control, it would be an easy upgrade. I never thought of upgrading mine before because of the daunting job of wire routing. The benefit of the digital thermostat is the precise temperature control compared to the analog t-stat and more importantly, when the AC fan is set to "Auto", the fan speed automatically changes before it completely shuts off as the inside of the cabin cools down to the set temperature.

WARNING! Before starting, read and follow all safety information and instruction in your AC manual to avoid personal injury. DISCONNECT/ UNPLUG THE RV 120 VOLT SUPPLY AND THE 12 VOLT SUPPLY FROM THE COACH BATTERY.

Remove AC the air distribution box, it is held in place by 4 screws located behind the air filters, you also need to removed the plastic control knobs in order to remove the air distribution cover.

 Unscrew the 3 mounting bolts pictured above.

 

With the divider plate removed.

 

With the electronic control box cover removed. The t-stat pigtails needs to be re-routed and should exit towards the left side of the box and the freeze control pigtail towards the right side. 

 

With the freeze control wire exiting the right side of box along with the quick connectors.

 

Using heavy duty plastic 3M "hoop-n-loop" fasteners.

 

With the control box "Velcroed" to the bottom of the AC base pan.

All wired up. I added an inline fuse just in case.

 

With freeze control wire inserted into the evaporator coil fins as per manual.

 

Wiring diagram of the electronic control box.

 

Divider plate reinstalled and mounting screws hand tightened, then torqued to specs. per manual. Do not over tighten or you may damage the unit base or the ceiling, and if bolts are left loose there may not be enough roof seal and may cause a leak. Reinstall the air distribution box and you are done! I did not remove the analog control dials on the air box; I thought it would be a good backup just in case the digital thermostat unit craps out when you needed it most.

The new single zone digital thermostat wall mounted control. It controls the AC, furnace, and the heat strip.

 

Things I did not like about the new t-stat:

• The thermostat display has no backlight.
• The current room temperature display is only viewable when the AC is OFF.