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Will Running an Air Conditioner in Cold Weather Damage It?

 

While most homeowners don’t want to cool their homes down in winter, some consider running their central air conditioner in order to test the system.  They may be making repairs or demonstrating to a potential buyer that the system is working.  In addition, home appraisers working on loan applications are required to inspect the HVAC system. Will running an air conditioner in cold weather damage it?

Running the Air Conditioner in Cold Weather is Not Recommended

Air conditioning manufacturers and HVAC professionals agree, an outdoor condensing unit should not be run in cold weather for any reason.  The cause of this prohibition is the oil used to lubricate the compressor. There’s a significant amount of oil in the compressor and it functions like oil in your vehicle’s engine.

Just like engine oil, compressor oil for condensing units has different grades. The oil that is used in central air conditioner compressors is summer-weight oil.  It is a heavy grade of oil that works well in warm conditions.  It can heat up and still provide the compressor with the lubrication and protection required, something lighter grade of oil could not do.  In cold weather, the oil is too thick for the safe functioning of the compressor.

Safe Weather Temperatures for Running an Air Conditioner

Most HVAC technicians and home appraisers won’t run a central air conditioner unless daytime temperatures are above well above 60 degrees F for at least 2-3 days prior to the test.  That doesn’t leave much time of the year for testing in some parts of the country.  In many instances, the appraiser has to note that he or she did not test the AC unit, being prevented by whether conditions.  Most say that they have never been asked by a loan officer to go back later and test the unit.  Usually, a visual inspection of the condensing unit, along with running the gas furnace or air handler indoors, is enough to satisfy the underwriter for the loan.  Running the AC is not a make or break part of the process.

Air Conditioner Sensors Prevent Cold Weather Operation

Some newer AC units are now equipped with low-ambient temperature sensors that prevent the compressor from turning on in cooler weather, protecting the unit.  That’s another reason most home appraisers won’t even test in cool weather.  If the unit doesn’t come on, they can’t know if the condensing unit has mechanical issues or if it’s merely protecting itself against damage from unsafe operating conditions.

What About Heat Pumps?

Heat pumps run in cold weather, obviously.  The difference is that heat pump compressors are filled with a lighter grade of oil that performs in lower temperatures.

Summary

Keep this tip in mind if you are showing your home in cold weather to a prospective buyer.  Explain to them why you can’t run the condensing unit.  You may have to assure them that you’ll fix the AC if it doesn’t work once warm weather arrives, and you’ll probably need to include that in the purchase agreement.  It’s a better choice than running the condensing unit anyway and risking an expensive repair.

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