Coleman 15K rooftop heat pump

RVcomfort gave you an over-simplified version of what really happens. The thermostat does not know if the furnace is running or not. When there is a 5-degree separation between the set temp and room temp, the thermostat "assumes" you want or need help from the furnace. If the heat pump by itself doesn't bring the room up to the set point over a time period, the thermostat "assumes" it's ineffective and that's when it gets locked out. There's an example of how it works in this document http://www.rvcomfort.com/rvp/pdf_documents/1976497.pdf.

I have like you sometimes wanted to use only the heat pump to raise the temp more than 5 degrees and found the furnace kicking on to be a nuisance. I've considered the toggle switch you mentioned, haven't done it yet. I often set the thermostat to 4 degrees above the room temp and walk it up as the room temp rises. Just another example IMO of poor design, optimized for those who don't care to understand how things work at the expense of those who do. If "electric heat" isn't working I'm perfectly capable of noticing that and switching to "gas heat".

Doug's solution seems the best way to go. the best heat pumps regardless of what they are installed on will only provide a 20* temp difference between cold air return and supply vent closest to the HP. Given your RV has about 280 sq. Ft. of space the HP might not be able to rise the temp you are looking for in many days of running. Is the savings in propane worth the expense of electricity? Follow Doug's advice.

Without propane on, then the furnace will not run.

The problem with a rooftop A/C is they do not have a defrost mode. IN home heat pumps, they turn over to the cooling mode and shut off the outdoor fan for about 4-8 minutes every hour or so. This defrosts any built up frost or ice on the coil, while slightly cooling the house.

Rooftop A/C units have a single fan motor to turn both blower wheels, and thus can not stop one. They also do not have any sort of defrost circuit. You can manually thaw your heat pump by running the cool mode for say 4 minutes, but it probably will take 15 minutes to make up as much heat as you lost in the 4 cooling.

I really wish they had a coil temperature sensor, that allowed them to run the heat pump mode until the return freon line was about 20F, indicating that the coil was covered in frost. Then shut off the compressor for at least 5 minutes, and keep running the outside fan. This will use air over 32F to defrost the coils (much like a walk in refrigerator does). If that sort of system where in use, then the heat pump would work well, even at 40F outside air temps. Yet that is not how they built most heat pumps for RV's.

I work on a lot of PTAC heat pumps at my work in Portland OR. They used to have a simple 40F outside thermostat, and would revert to back up electric heat when it was under 40F outside, and change back to heat pump mode around 45F. But the latest version is digital control, with a temp sensor on the freon line, so it can run more often in the heat pump mode than the electric mode.

It makes a huge difference - in heat pump mode it draws about 4 amps to make 9,000 Btu's at 208 volts. In electric mode, it is 12 amps and 8,000 But's.

Fred.

Once the furnace kicks in due to the 5 degree separation setting, the HP comes on line at the 5 degree mark. Once the RV is AT the set temp, the HP will KEEP it at the set temp without the furnace coming on again. Just use the furnace for that initial heat up. Doug

I would try your switch and see what it does.