A common problem with these units is the RV Comfort thermostat hanging up. This is caused by stray RF interference. Fluorenct lights, inverters, etc. have been found to be a source of this problem. The way the system works is the thermostat controller requests an acknowledgement from each device, AC, heat pump, furnace, etc. every second. If it doesn't get a response, the controller locks up in several different ways, usually staying in the last setting except for the device that failed. It can also display an 88. and completely lock up. You can reset it easily by turning the thermostat off, removing the cover from the thermostat, and removing the fuse. Wait between 5-7 minutes. This forces the controller to reset. Replace the fuse and turn the thermostat back on. This will often return the systen to operating mode.
RV Coleman has a new upgraded thermostat with better logic that, when a failure occurs, the controller will continue to request an acknowledgement for to 60 seconds. If during that time, it gets an acknowledgement, it discards the failure and keeps running. This has solved at least 99% of or issues. Good luck.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))
2003 Fleetwood Expedition 38N 2005 Saturn Vue