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Old 11-23-2018, 07:34 PM   #1
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Dometic AC Heat Pump Icing Over

Anyone have any issues with the heat pump on the main AC unit icing up?? Wondering how to fix this? Thanks!Click image for larger version

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Old 11-23-2018, 07:44 PM   #2
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How cold is it outside?
Below 40į heat pumps are basically running but not producing heat and have a tendency to freeze up. There just isn't enough heat in the air at that temperature to be efficient, especially if raining or high moisture/humidity.

Home A/C units often turn off/cycle and/or have a heating blanket to prevent icing.
R/V units do not.
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Old 11-23-2018, 11:52 PM   #3
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Itís been high 40s during the day, high 30s/low 40s at night. And yes, raining always (Seattle). Good info, maybe switch to propane heat this time of year?
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Old 11-24-2018, 04:37 AM   #4
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Hi, here is a link to the Dometic heat pump manual. Check out the section on defrost.

It is possible there is an issue with the timer sequence (usually a circuit board) that controls the defrost cycle or reversing valve (the refrigerant valve the changes the flow from heat to defrost, which is actually the a/c cycle by the way). Also, low refrigerant charge or defective outdoor fan/fan relay could be the culprit.

I have worked on tons of heat pumps but Iíve never pulled one of these apart yet. I have the same unit on my rig so Iím sure at some point Iíll get a chance.

There is also the possibility that because of continual excessive moisture and cooler temps the defrost cycle simply canít keep up. Even though the air temp is in the 40s, the coil temp is way below freezing so with all the moisture, you make ice like crazy. It should be designed to handle it but like most RV stuff, who knows what design conditions they used to design these things.

In any case, with this much ice on the outdoor coil you are getting very little heat out of this unit and continuing to run it in this condition can cause damage to components like the compressor and outdoor fan motor.

You should change over to gas heat until you can troubleshoot the unit.

Best of luck,
Ed

http://manuals.dometic.com/download.php?file=1926
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Old 11-24-2018, 07:38 AM   #5
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Thank you!
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Old 11-24-2018, 01:20 PM   #6
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Running backwards

Quote:
Originally Posted by 5picker View Post
Home A/C units often turn off/cycle and/or have a heating blanket to prevent icing.
R/V units do not.
Actually home heat pumps run backward (that is, run in A/C mode) to de-ice. They also run the electric resistance heating strips when de-icing, so you usually don't notice it.

Here in the mid-Atlantic states, a lot of heat pumps have been installed where they're not really ideal. We like to kid about trying to heat a room to 70 degrees by pumping 70-1/2 degree air into it.

Larry
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Old 11-24-2018, 06:39 PM   #7
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I'm an hvac guy. A heat pump works even when temps are below freezing because their is still heat it is grabbing from ambient air. It's just not as efficient as the heat strips energize to supplement. In your instance you could have several problems. You could be low on refrigerant, dirty filter, malfunctioning defrost system, or you could also be parked under something that is dousing more water than usual on your unit. That unit gets cold up there and water will begin to freeze on it given the right conditions. Get up there with some hot water and douse it down. Turn the unit off first. If it freezes like that in dry conditions then suspect defrost board.
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