Coleman 15K rooftop heat pump

I would try your switch and see what it does.

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

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.

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.

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".

Wayne Dohnal wrote:
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".

RVP decided that IF there is a greater temp called for than 5 degrees, you would have to run the HP a very long time to heat up the RV. So, they have the Furnace come ON if you set greater than the 5 degrees. IT DOES NOT LOCK OUT THE HP IN THIS SCENARIO. The HP is on standby and if the set temp gets to that 5 degrees with the furnace, the HP comes on and heats the rest of that 5 degrees. Normally, unless you have an extreme blue norther hit you and the outside temp drops dramatically, when the inside needs more heat, the tstat calls for Heat and the HP will come on and heat that next cycle. And continue doing so. Doug

dougrainer wrote:

Wayne Dohnal wrote:
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".

RVP decided that IF there is a greater temp called for than 5 degrees, you would have to run the HP a very long time to heat up the RV. So, they have the Furnace come ON if you set greater than the 5 degrees. IT DOES NOT LOCK OUT THE HP IN THIS SCENARIO. The HP is on standby and if the set temp gets to that 5 degrees with the furnace, the HP comes on and heats the rest of that 5 degrees. Normally, unless you have an extreme blue norther hit you and the outside temp drops dramatically, when the inside needs more heat, the tstat calls for Heat and the HP will come on and heat that next cycle. And continue doing so. Doug

They said something about the cycle trying 3 times and then it would lock out heat pump for 2 hours.

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".

RVP decided that IF there is a greater temp called for than 5 degrees, you would have to run the HP a very long time to heat up the RV. So, they have the Furnace come ON if you set greater than the 5 degrees. IT DOES NOT LOCK OUT THE HP IN THIS SCENARIO. The HP is on standby and if the set temp gets to that 5 degrees with the furnace, the HP comes on and heats the rest of that 5 degrees. Normally, unless you have an extreme blue norther hit you and the outside temp drops dramatically, when the inside needs more heat, the tstat calls for Heat and the HP will come on and heat that next cycle. And continue doing so.

Yes, that is correct, but that is when the system cannot function normally and heat up the Interior. The sequence is for when you initially get into a subcold RV and you need the temp raised more than 5 degrees. When the system has reached the temp OR the inside temp is within that 5 degrees the HP will function normally. Doug

This thread gives the a good opportunity to gripe about another bad RVP heat pump design detail: Operation of the optional auxiliary heat strip. The heat strip is triggered automatically in the 35 to 40 degree ballpark. When the temp goes below the switchover point, the heat strip runs instead of the heat pump. Like all heaters, when the heat strip is used after sitting idle for months, it smells for a few minutes. When I de-winterize I run the furnace with the windows open for as long as it takes to get rid of the smell. Can't do that with the aux heat strip, because the automatic design won't allow it (unless you're de-winterizing in near freezing weather). So when you hit the first cold day while camping and the aux heat comes on, it stinks like heck, and the only thing you want to do is shut it off. You want heat, not open windows to get rid of the smell, when it's freezing out. Because of this automatic-only operation, the aux heat strip is a mostly unusable feature. After getting hooked by it this spring I did add a switch to force the switchover manually, but what a pain to have to work around all these automatic things that should make life easier, not harder.

I've not gotten the point of a heat pump in a RV at all because of the single motor fan design. Why not just a regular A/C and a heat strip, although the best bang for the buck is a Cheap Heat system to supplement the RV furnace, and not bother with semi-working heat solutions from a device designed to cool the environment.