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Old 08-26-2015, 04:04 PM   #1
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Join Date: Jun 2015
Posts: 13
Heat pump fan cycling

It has started to cool off at night here, not enough to use the propane furnace, but enough to run the heat pump in my 2016 30ds.

The heat pump blows warm air and I can hear the compressor running so I think that part is fine.

However, the fan that moves the air throughout the rv's ducts cycles on for 7 seconds or so and then shuts off for a minute, in a repeating cycle.

The colder it is it seems that the fan runs a little longer before shutting down.

I have tried the fan selection in all speeds and auto. Opening the bypass vents on the unit doesn't seem to change anything.

Is this normal? Or a problem I could fix, or shall I schedule a warranty visit?

Thank you

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Old 08-26-2015, 05:41 PM   #2
Join Date: Aug 2015
Location: Central Illinois
Posts: 56
Not that I am an expert on the unit on the fr3 but I do have 25 years of experience in the HVAC business. First blush is that the operation in heat pump mode the fan cycling could be normal for that particular unit. The cycling could be the thermostat or a discharge air temp sensor. Since you mentioned the fan stays on longer when it is colder outside, try raising the set point of the thermostat a couple of degrees and see if the fan stays on longer.

Remember the outside unit on the roof will go through a defrost cycle and since the condenser is very small it will defrost often. The manufacturer may even have the controls set so the unit heats for 90 seconds or so and then a short defrost cycle. They never let it the condenser get too cold as it could ice up and take a long time to get the condenser thawed out.

If the discharge air temp sensor is in play then when the fan comes on the sensor cools off and turns the fan off to warm the evap coil again and then repeats.

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Old 08-26-2015, 05:56 PM   #3
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Join Date: May 2015
Posts: 48
Read the manual on it. I seem to remember something about the outside temperature being in the 40s that the unit will reverse cycle to defrost the unit. The interior fan shuts down when this happens. These heat pumps do not work at very cold temps.
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Old 08-26-2015, 08:53 PM   #4
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Funny. I just noticed this today as it's the first time we have used ours as well. Warmed up pretty quickly, though we were only in the mid 50's overnight. I also was going to read the manual, but was quickly sidetracked by the wife with adult beverages.
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Old 08-26-2015, 10:00 PM   #5
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We just had ours installed and are in northern Michigan, so we need it in heat mode. I noticed this also and called Atwood tech support. They said this is normal operation for their unit. I think the idea is to keep the air temp consistent throughout the coach. It is different, but I am happy to have a heat pump.


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Old 08-27-2015, 02:25 AM   #6
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Thank you all!

It has not been cold enough to need the defrost cycle 60-65 so I kept digging.

I found the service manual online this evening and I was able to enter into one of the service modes that showed realtime read outs of all the thermistors.

The main board temp appears to be driven by the return air and controls the interior fan. This temp rises rapidly when the interior fan kicks in while the panel temp doesn't change.

It appears the heat pump unit is working properly but warm air output is leaking into the return air side causing the circulation fan to short cycle. While the control panel sensor is not getting warm enough to stop the heat cycle due to the cabin temp.

When I get a chance I'll pull the cover and see what can be done to stop the air from intermingling due to the leaks, and see if it helps the fan run longer and cabin warm to the set point.

I'm including the manual pages from both the thermistor viewing mode as well as the troubleshooting page that apply in case others have similar issues down the road.

I agree it is really nice to take the chill out of the rv without using propane.

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Old 11-10-2015, 10:26 AM   #7
Join Date: Apr 2015
Location: Thousand Oaks, CA
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Thank you for that info, pantanke.

Our heat pump has similar behavior, except that the cabin temp never changes, because the compressor doesn't run long enough to accomplish anything. The same thing happens when in Cool mode. The cabin doesn't cool down, because the compressor only runs for a few seconds, and then shuts off.

In both cases, it acts like the A/C thinks the cabin has already reached the desired temperature. I'll bet it's because of an air leak, as you suggested.
2016 FR3 30DS
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Old 11-24-2015, 09:23 AM   #8
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I have the same issue in my 2016 FR3 32DS (Atwood AirCommand 18K BTU). Its in the 50s outside and I have both thermostats set to auto/auto. What I set the temp to doesn't seem to matter too much. It runs as expected for a while and then thinks its reached temp and starts doing the 7 second cycle all night. If you raise the thermostat by 2 degrees it runs normally again until it thinks its reach temp. To keep the coach warm overnight I ended up with the thermostat set to 78 starting at 70, then 72, and so on.
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Old 01-19-2016, 11:18 AM   #9
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Patanke, just curious if you have found a solution to the warm air output leaking back into the return and messing with the on board thermostat?
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Old 01-23-2016, 01:27 AM   #10
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I pulled the inside cover and duct taped all the seams and joints in the return side (sucking half) that I could reach. I also closed off the blowing side of the ceiling unit as well as the ceiling vents nearest the unit. It helped a lot but did not totally fix the problem.

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