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TOPIC: Running the AC on heat pumps during cold weather.

Running the AC on heat pumps during cold weather. 10 years 6 months ago #47025

Since we are trained to not run the AC during cold weather, what about when the unit is a heat pump? Does this make a differance? After all, when running on heat mode we are running the AC compressor so it should be warmed up enough to use in cooling mode?
Thanks for the advice...

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Re: Running the AC on heat pumps during cold weather. 10 years 6 months ago #47027

Just attended a 4 hour class put on by the East Coast Tech Director for Lennox.  He stated his manufacturer and the other top 2 (Trane & Carrier) are most concerned about the difference between the outside temp and the inside temp. 

The inside temp air will flow over the coils.  He is looking for at least a 10 degree difference between inside and outside.  If a foreclosed home with inside temp of 60 and outside temp of 60, no heat will be exhanged.  If outside temp of 30 but inside of 60, the air temp is 30 degrees different and the HVAC system will have no problem.  He also stated you can flip back and forth between cooling and heat as fast and as often as you like with no damage to the equipment.

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Bruce Ramsey, ACI

Re: Running the AC on heat pumps during cold weather. 10 years 6 months ago #47043

I don't understand about anything you said except the last line that relates to this question?

You can not evaluate the unit in cooling in the cool season, but you can run it and see if the parts work.

My procedure is to run the HP in heat(without the auxiliary heat), then the aux. heat, then with the house up to a normal temp is switch over to cooling.

If you run a heat pump with the same indoor-outdoor temps in some winter regions you may not get a refrigerant pressure differential to operate the reversing valve. This does no damage to the equipment, but you may think it's broken.

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Re: Running the AC on heat pumps during cold weather. 10 years 6 months ago #47051

Outside of verifying if the reversing valve is switching, what possible benefit is there to running the heat pump in cooling mode in the winter? The heating mode will indicate if the system is transferring heat and frankly checking a temperature differential isn't the end all of A/C tests anyway.

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Title: Home Inspection Peoria, IL
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Re: Running the AC on heat pumps during cold weather. 10 years 6 months ago #47091

How long does it take to purge the oil from the freon when the power has been cut off? I had one hum for about an hour but never came on. It was a heat pump but it was not cut on. it i got there. It was about 50 when I got to the home.

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Re: Running the AC on heat pumps during cold weather. 10 years 6 months ago #47127

24 hours is the recommended waiting period.

This can be accelerated if you have the appropriate tools.

It is about outgassing the refrigerant from the oil, not purge the oil from the Freon. It's all relative to temperatures in the previous 48 hours. That's the indoor temperatures in the outdoor temperatures of the equipment. High temperatures on the indoors drives refrigerant to the exterior cold equipment where it migrates into the oil. Depending on the pressure differential between outside and inside and temperature determines the time.

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Home Inspector
HVAC Systems Design
ITC Level III Thermography - Building Science Thermographer
Thermal Imaging
Serving Clarksville - Nashville TN and the Mid TN area
www.MidTnInspections.com
www.ThermalImagingScan.com
To link to my pages:
www.midtninspections.com/link-submission
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