There are a lot of issues with RF affecting these thermostat controllers. The way the system works is the thermosatat ecu poles the attached units ACs, Heat Pumps, Furnaces, etc. every second. If it doesn't get a response, the system locks up and holds the last setting or displays a 00 in the display. This is usually caused by stray RF being developed by any of several sources, most notably the fluorscecnt lights, and the inverter. the coach manufacturers typically don't use shielded wire for the thermostat to other units, so the RF can easily get on the control wire. RV Comfort recently developed a new and improved thermosatat controller that senses a fault, then continues to pole the devises for 60 seconds before it takes action. If the fault goes away, nothing happens, if it is still there the ecu goes into lock up.
There is a simple way to reboot the system, simply remove the small glass fuse in the thermostat, and wait 5-7 minutes. This forces all systems to reset. When the fuse is replaced the system will go back to working.
You said you replaced the thermostat, look on the control board on the left side and see how many pink dots you have on the board. If it's only one dot, that is the oldest version and very suseptable to RF. If it has 2 dots that is the upgraded board, and better but still not the best. If the display on the board is a large lcd and the buttons are more solid than the others, you have the latest board. Sorry this is so long, but I wanted to give you all the info I have.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))
2003 Fleetwood Expedition 38N 2005 Saturn Vue