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Heat Pump Fan Cycling

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bobkbusch

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Heat Pump Fan Cycling
« on: June 06, 2022, 01:20:47 pm »
I have a 2022 2552 with two Dometic ac/heat pumps.  I’m camping in Grand Teton NP where the temps are dropping to the low 30s at night.  I have my front unit set to heat pump at night with the fan speed set to “ LO.”

This does a nice job keeping the coach warm and the constant fan noise helps us sleep.  However, after 5 or 6 hours, the fan shuts off for a minute or so.  After a minute or so, it starts up again and then randomly shuts off/starts up the rest of the night.

Anyone else experience this? Is the fan stopping for a deice cycle?

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mikeh

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Re: Heat Pump Fan Cycling
« Reply #1 on: June 06, 2022, 04:14:16 pm »

Bob, I can't tell you why it does it because I've never investigated--but my unit does the same thing on both cooling and heating settings of the heat pump.
It has always done that and it doesn't seem to affect performance in any way, so I've just not worried about it.  I would be interested, however, if you happen to discover the reason.
Mike

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parkgt

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Re: Heat Pump Fan Cycling
« Reply #2 on: June 06, 2022, 06:31:09 pm »
Why not call Dometic?  Might even reach a human that can answer the question.

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CalCruiser

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Re: Heat Pump Fan Cycling
« Reply #3 on: June 06, 2022, 07:48:56 pm »
Is your Dometic  an actual heat  pump, or just an air conditioner with an electric heat strip?
Regulating a resistive heat strip requires a programmable PID controller to vary the amperage, but a fan can be switched on and off by a simple thermostat. Just a SWAG.
Goin' where the wind goes...

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bobkbusch

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Re: Heat Pump Fan Cycling
« Reply #4 on: June 06, 2022, 10:11:32 pm »
Tried calling Dometic, but so far haven’t reached an “expert.”  Also spoke to Doug at PC, but he hadn’t heard of the issue, and wasn’t able to provide an answer.  BTW, he is always super helpful and knowledgeable if I call for help! 

I have a heat pump, not heat strip.

I did find this…possibly related… post #18 in the linked thread.

https://www.forestriverforums.com/forums/f15/heat-pump-question-now-that-cold-season-has-arrived-196478.html#post2225272

« Last Edit: June 06, 2022, 10:16:33 pm by bobkbusch »

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bobkbusch

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Re: Heat Pump Fan Cycling
« Reply #5 on: June 08, 2022, 06:56:05 am »
After more research and a little bit more “experience,” here’s what I believe is happening.  This is my first RV with a heat pump, so I’m learning as I go.   Apparently, heat pumps don’t work well below 40 degrees.  They will start going through more defrost cycles as the temperature gets colder. 

In my case, although the fan was set to constant “LO,” the fan would shut off as the unit was presumably going through a defrost cycle.  As the temp dropped below 40, the unit kept working, but went through more frequent defrost cycles.

Last night, at 2:30 am, I woke up because it was 80 degrees ((I have a portable thermometer) in the bedroom area!  The front thermostat was set to Heat Pump and 66 degrees.  However, I noticed the display was blinking between Heat Pump and Furnace.  The heat pump wasn’t running but the furnace was.  Apparently there is some logic that below a certain outside temperature, it will automatically switch to the furnace.  I’m camping in Yellowstone and the outside temp had dropped below freezing.  Not sure how low, but the outside hose was frozen. 

The temp differential between the forward thermostat and bedroom actual temp was 14 degrees warmer in the bedroom due to only one furnace vent forward of the bedroom.  Next trip, we will bring our ceramic heater and try to balance forward and aft temps better.

Also, just for grins, I tried to turn the rear heat pump on, using the bedroom thermostat, but it wouldn’t even turn on, most likely due to the outside temperature in the 20’s.

Time for a nap…




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custerhank

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Re: Heat Pump Fan Cycling
« Reply #6 on: June 08, 2022, 03:39:42 pm »
You are correct about the heat pump switching to furnace below a certain temp. Kind of depends on heat pump model but below 40 is a good guide. We too use an electric space heater and it works great in our "large" model 3100. We place it at the front behind the cab seats and it handles the whole coach. Much more efficient (and quieter) than using the furnace. The heat pumps in our previous several motorhomes all worked like this.

Not to hijack this thread, but, we have a heat pump in the front and the "add-on" A/C (manual controls) in the rear of our 50-amp unit. We too use the Fan-on-Low at night to drown out noise. A couple nights ago the heat pump started to clatter/chatter a bit on Low. Last night I switched to High fan and it seemed to quiet down. Did not expect a heat pump issue on a 2019 model already. Is my fan starting to go? We will be on the road another week and then must head home so no lengthy service right now if we can help it. But also do not want to blow something up.

Hank
Hank & Joyce Whitney
Custer, SD
2019 PC Model 3100

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Free2RV

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Re: Heat Pump Fan Cycling
« Reply #7 on: June 09, 2022, 05:30:11 am »
Bobkbusch, I think your conclusion is correct for the reason your heat pump is starting and stopping.  We have the same issue on A/C with ours when it is very humid.  The unit goes into a defrost mode, starting and stopping with changes to the fan speed when it does it.  Our research determined that it was to defrost the cooling coils of the A/C.  They say it is designed to do that and not to worry about it.  I suspect the same is true for the heat pump because ours did the same as yours when we used the heat pump in "cool" weather. 
We ended up getting a ceramic heater and using it at night and it keeps the unit very comfortable instead of having the furnace run.  We set ours on the floor in front of the kitchen cupboards and plug it into the power tower outlets on the kitchen counter.
Gary

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bobkbusch

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Re: Heat Pump Fan Cycling
« Reply #8 on: June 09, 2022, 11:20:42 pm »
Thank you guys for the feedback!