Modify RV Air Conditioning System Digital Thermostat

December 26, 2016 Trailer Mods / Repairs


There are significant differences in the way RV systems work in comparison to home systems. My goal with this mod is to move those differences in air and heat closer together. We have totally separate heating and air conditioning systems, the short falls are there is little air movement when the heat is running and Gas furnace, alone, really tends to dry out the air, moreover, neither unit has a particularly accurate thermostat, this mod fixes that.

Changes in the System

Removing the analog thermostat and replacing with a digital is key to the entire operation. We are well aware of our optimal winter and summer temperature preferences and analog is so difficult to set up. Digital tends to be more “set and forget”. We plan to run the fan in the AC system with an electric heat element to warm the air without drying it so much, and whenever the gas furnace does operate we want the AC unit to help distribute the heat (air) more evenly.

Parts Required

Parts in the RV:

  1. Coleman 48000 Series (48203) Roof Top AC System (Mechanical Controls)
  2. Atwood AFSD12 Furnace
  3. Atwood Mechanical Thermostat

Parts necessary to perform Mod:

  1. Coleman 9330C755 heat ready control box
  2. Coleman 9233A4551 heat kit
  3. Coleman 6536A3351 2 Stage Heat Pump Digital Thermostat (12VDC)
  4. Altronix Timer Relay (2)
  5. 3 General purpose Diodes

We will provide a schematic of our hook ups for this unit below.

The Mechanical controls on both heat an AC systems are to be removed for this mod.

Video Description of Mod Testing


This mod operates very well. We, actually, also carried an oil filled space heater along and between the space heater and the heater in the AC we never once had the furnace kick on. This trip we camped out in 20 degree weather in a significant cold snap in north Texas, just before Christmas. We also have very accurate control of the AC and Heat Temps and this all totally worked better than ever before. In this mode of operation, we are completely hooked!!

Realize, however, the AC and Electric heat will only work when connected to 110 V …. heat from the furnace will always work with 12VDC. Boondocking is no problem in the wintertime. For this mod to work, and clearly to have AC, one must use a generator or inverter to create 110V while boondocking.

Support Documents

Schematic is not available at this time …. leave a message or subscribe to this post and you will be notified when it is available.