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Common Causes of Air Conditioning Freeze-Ups

common causes of ac freeze ups
Reading Time: 2 minutes

A frozen air conditioner is a very common occurrence. Let’s have a look at the why’s of a frozen AC unit and what needs to be done before repairs can be made. Typically, there are three things that cause a unit to freeze.

The first is a lack of air flow. A lack of air flow across the indoor coil can be caused by an extremely dirty filter or the coil inside the air handler itself is very impacted with debris. You, as the home owner, can prevent units from freezing up simply by changing your filter on a regular basis. Depending on the filter the interval can be anywhere from 30-90 days. Of course, every home is different. Very simply I recommend checking the filter every 3-4 weeks and if it looks dirty change it. Impacted coils are generally caused from a lack of maintenance to the unit and or not changing the filter. If the coil is impacted DO NOT attempt to clean it yourself. You will very likely create damage to the coil that could lead to needing the coil replaced which can be very costly vs. having a professional perform coil sanitation.

A refrigerant leak is the next most common cause of a frozen air handler. I won’t bore you with a big long air conditioning lesson; the long story short version when it comes to refrigerant is it travels from the indoor to the outdoor unit in the copper lines that run between the units. The refrigerant changes back and forth from a liquid to a gas as it travels through the indoor and outdoor coils thus absorbing and releasing heat. This change of phase happens only when the levels of refrigerant inside the system are correct and operating at the correct pressures. If the pressures drop too low it will make the entire refrigerant circuit freeze. You just do not see the outside unit freezing as typically the heat of the day melts the ice on the outside lines. Again, if you have a refrigerant leak you will need to turn to the professionals for help.

Eskimos are guilty of the third reason coils freeze. I said Eskimos because the third reason is people set the thermostat below 68 degrees. In a properly working air conditioner the coil operates 20-25 degrees below whatever the thermostat is set at. If you turn the thermostat down to 60 degrees our coil can be running at 45 degrees, combine that with a slightly dirty filter and coil and boom… frozen coil.

What do you do if you find yourself with a frozen coil you ask? We will need you to head to the thermostat and set the button that says heat/off/cool to off and then set the fan button to on. This turns off the outdoor unit and sets the fan to run constantly. We cannot fix a frozen coil if it is still frozen when we arrive.  This turns off the outdoor unit and we stop the refrigerant from cycling, stop the coil from freezing and the air movement will thaw the coil. I suggest putting some old towels or some other means of catching water as the coil thaws to prevent water damage to the home. A frozen coil can hold a couple gallons of water depending on how long it has been frozen.

Okay my friends, after all this frozen talk and I think I want a margarita, until we meet again May the Force be with you. House Whisperer out!!       


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