Heat pumps

[Retired tom]

2008 monico diplomat, I have two heat pumps on the roof, temp got down to 20 last night so I thought I would go out this morning and turn the heat pumps on. I first turned on the gas furnace for 5 minutes then shut the gas fce off. Then I turned on the heat pumps but they would not start, but air would start blowing out the floor vents, just air not heat. How can this happen the heat pumps are not ducted to the floor vents are they. Any one got any ideas.

[00 Buckshot]

20 degrees is too cold for the HP's to work. I suspect your system defaults to the furnace and it was cold air when it first came on.


Hope that is all it was.

[BCam]

If you have a Coleman, "basement air" heat pump system, there are some non-intuitive running characteristics when in heat mode. The details can be found here (pgs 5-10):

http://techsupport.pdxrvwholesale.co...ice-Manual.pdf

This is applicable even if yours isn't the exact same model number, they're all pretty much the same except for the duct connections.

[Retired tom]

Thanks will try when warmer

[Newmar2856]

My heat pumps won’t work when it’s under 40 degrees. I usually revert to the furnace when it’s going to be 45 or below.

[TXiceman]

Most of the RV heat pumps will not start the heat pumps if the interior temperature is more than 5 degF below the thermostat set point. It will bring on the furnace. If it is . below 40 degF outside, don't even bother with the heat pumps.

You need to get or download the manual for your thermostat and see the sequence of operation for the unit.

Ken

[DFord]

There's no escaping the fact that RV heatpumps only have one blower motor and there's no way turn off the outdoor fan which is required to defrost the outdoor coil. The outdoor coil will always frost up below 40 degrees F and must be defrosted. There's an outdoor thermostat that prevents operation below 40 degrees F.



(The heatpump in my house doesn't have that limitation. A couple of days ago, we had temperatures down below minus 10 F. Of course, it needed a boost from the auxiliary heat strips to keep the house warm but the compressor never stopped capturing as heat as it could from the outdoor air. Every 90 minutes, it went into a defrost cycle where the outdoor fan stops while the heatpump becomes an air conditioner for a few minutes until the outdoor coil is warm enough all the ice is gone.)

[tmw188]

Originally Posted by BCam

If you have a Coleman, "basement air" heat pump system, there are some non-intuitive running characteristics when in heat mode. The details can be found here (pgs 5-10):

http://techsupport.pdxrvwholesale.co...ice-Manual.pdf

This is applicable even if yours isn't the exact same model number, they're all pretty much the same except for the duct connections.

No he said he had two rooftop units.

[jacwjames]

Originally Posted by DFord

(The heatpump in my house doesn't have that limitation. A couple of days ago, we had temperatures down below minus 10 F. Of course, it needed a boost from the auxiliary heat strips to keep the house warm but the compressor never stopped capturing as heat as it could from the outdoor air. Every 90 minutes, it went into a defrost cycle where the outdoor fan stops while the heatpump becomes an air conditioner for a few minutes until the outdoor coil is warm enough all the ice is gone.)

Yup, we got down to almost 0F on Saturday AM and the heat pump was still operating and I don't think my heat strips were coming on as I never saw them on the thermostat.

When the system was installed in 2017 I wanted a high seer system plus 6" exterior stud walls and a foam flash prior to R19 batt insulation and +R40 in the ceilings, the house is very energy efficient.



With newer technology in regards to HVAC systems I'm surprised the RV industry hasn't improved the roof AC's to run at lower temperatures.

[Persistent]

RV's require light weight and compact design. Evaporator and condenser radiators are small and inefficient. They condense moisture that freezes on the evaporator side. Active defrosting is required.

Home systems can have much larger and more efficient radiators. Some even have two external radiators so one can be defrosting while the other is still providing heat. (Much more expensive.)

The next step up is in-ground evaporator. Ground temperature rises as you go deeper. These can continue to work even at very low outside temperatures. Ground temp is 50 degrees in Wisconsin if you go down 20 feet. Air temperatures drop to -20 degrees F.

Installation cost is extremely high. Sometimes a well is drilled and 50 degree ground water is used for the evaporator. Water is recycled back into the ground. (Not always permitted by law.)

I know, I am Persistent and annoying. I can't resist.

[96 Wideglide]

Originally Posted by DFord

There's an outdoor thermostat that prevents operation below 40 degrees F.

Not on mine!

Few weeks ago I was getting 85F heat out of one when it was 35F outside.

[groveln]

I completely covered (cut to size) my two Coleman 9000 Mach Polar plenums with Thermo-Tec heat & insulation product. Since they're just HVAC tin it seem to make sense to me if I insulate them from excessive heat of the summer & cold of the fall/winter they'd be more efficient doing both jobs & I haven't been disappointed. They sound quieter being dampened by the insulation. They are original EQ on my '04 American Eagle & have performed flawlessly & I also installed Micro-air Easy Starts on both hoping to get many more years out of them.

[TXiceman]

Originally Posted by DFord

There's no escaping the fact that RV heatpumps only have one blower motor and there's no way turn off the outdoor fan which is required to defrost the outdoor coil. 8-.)

The Coleman Mach * units have separate evaporator and condenser fan motors.

Another point is the air is blown over coils, not radiators.

Ken

[Retired tom]

Worked fine when it warmed up. Thanks