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Old 01-21-2016, 10:15 AM   #1
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Heating at zero degrees

I had an interesting experience running the heater in our Forester 2401R while extremely cold out (zero degree range) when charging the batteries with the generator (AC power on, not plugged in to outside power). I turned the thermostat's fan setting to HI and then to Furnace with the thermostat set high (80). The furnace came on with the fan on high and put out good heat but the heat pump/AC fan also came on. It just blew a lot of cold air into the house and didn't seem warm at all. The heat pump is not even supposed to work at this temperature so I was surprised it was on at all. I then found if I switched the fan speed to either LO or AUto, the furnace worked normally without the heat pump. Does anyone know why the heat pump would come on at the HI setting in this temperature range and whether or not this is normal? Thanks!


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Old 01-21-2016, 06:13 PM   #2
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I'm actually surprised it does not run all the time on the LO setting as well (mine runs on both Hi and Lo). Leave it on AUTO and the only fan that will run is the furnace fan (at least that's how mine works).
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Old 01-21-2016, 06:41 PM   #3
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See Fan mode middle of page 9: in attached manual. Fan mode should be Auto.
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File Type: pdf Dometic Thermosat.pdf (1.40 MB, 91 views)
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Old 01-22-2016, 05:46 PM   #4
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Thanks Major and Flybob! Good to know and certainly glad it's not a defect.


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Old 01-23-2016, 12:59 PM   #5
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When using the furnace, we also found out that you should have your fan on auto. That is normal
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Old 01-23-2016, 12:59 PM   #6
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The reason it works when on HI is because it is assuming that you don't have enough heat, which is why you chose HI. Therefore, it is trying to supplement the furnace heat with the heat pump in order to get your coach up to the temperature you are trying to achieve.
It may not have actually been pumping cold air. A heat pump doesn't supply really warm air. However, it DOES send out air that is warmer than the room temperature, but because it is blowing, it is perceived as cool to the skin. If you put a temp gauge in the outlet, you may see that the air is warmer than the room air by a few degrees. If it is not, then there is something wrong with your heat pump and you need to have it serviced.
Additionally, residential heat pumps have emergency heat strips that will supply heat electrically if something is wrong with the compressor portion of the unit. Not sure if that is the case with RV units.
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Old 01-23-2016, 01:42 PM   #7
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Are you sure the heat pump was on? Normally the heat pump will not work when it is that cold out. Maybe it was just the fan blowing since you had it on manual high and turned to the furnace setting. I do not think you can turn the furnace and heat pump on.
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Old 01-23-2016, 09:59 PM   #8
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No, the heat pump was not on. It was simply the fan blowing cold air around. It's a logical fault, because the heat pump does not run at this temperature range, however if you select LO or HI, the fan comes on. It thinks you want the AC/heat pump fan on (not just the furnace fan) even though it's 0 out. They actually should change this (and with the thermostat, the system DOES know what the temperature is). But under the current setup, AU gives you the furnace fan and it automatically selects HI speed if the temperature differential is >5 degrees.

The fact that the heat pump is not running is proven by this from the Dometic thermostat manual:

Low Ambient Heat Pump Lock Out
All heat pumps are constrained to operation at a temperature range that is determined by outside conditions. Since all heat pumps lose their efficiency at low outside ambient temperatures, the Dometic heat pump has a lock out feature that prevents heat pump mode of operation when temperatures fall below 30 F. If you have the system set in the Auto Mode the fan will be turned OFF. Only the fan will remain ON if the fan setting is set at Low or High, however the compressor will not run and there will be no heat function below 30 F.


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Old 02-12-2016, 09:29 AM   #9
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Simple solution the thermostats fan setting only controls the fan connected to the AC/Heatpump. Furnace setting only controls furnace. So it is possible to do just what happened, as you set both at same time. If you go back into fan setting and set to off the AC/Heatpump fan will not run. I will occasionally run the AC fan in zone 2 to help move air while the furnace is on.
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Old 02-12-2016, 10:24 AM   #10
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Quote:
Originally Posted by Rich5117 View Post
Simple solution the thermostats fan setting only controls the fan connected to the AC/Heatpump.

* Of course, that is true -the fan control sets the fan only.

Furnace setting only controls furnace.

* Incorrect. The furnace setting also turns on the heat pump fan as demonstrated by me and confirmed here by others, if the fan is set to HI (and as others have reported, to LO, which I have not confirmed or disproven).

So it is possible to do just what happened, as you set both at same time.

* You have to set the fan to something, so when you turn the furnace on you have always set both in some manner.

If you go back into fan setting and set to off the AC/Heatpump fan will not run.

* There is no fan off setting. There is only system off including furnace. The solution to run the furnace but not the heat pump fan is set the fan to AU.


I will occasionally run the AC fan in zone 2 to help move air while the furnace is on.

*Thank you, however I do not have zones. Also A/C and furnace are separate settings that cannot both be on with the Dometic single zone thermostat.




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