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Concerns for a Frozen A/C Unit

Frozen AC

A common problem with air conditioners is the indoor evaporator coil freezing up. A frozen A/C unit can't cool your home and may not work at all. If this happens repeatedly, frozen evaporator coils can damage your central cooling system.


  • Insufficient airflow across the evaporator coil.In a central air conditioner, the indoor evaporator coil draws heat energy from the air as pressure is reduced on refrigerant flowing through the the coil. This makes it convert into a gas and become cooler. If not enough air flows across the coil, the refrigerant can't absorb much heat. As a result, its temperature will continue falling and the coil may freeze up. The airflow may be restricted as a result of a clogged air filter (which should be replaced) or a dirty evaporator coil (which can be cleaned). Check registers and vents to make sure nothing is blocking them. Kinked or leaking ductwork also can impede airflow.
  • Low refrigerant level.An air conditioner that's leaking refrigerant, or didn't get enough in the first place, can freeze evaporator coils. The lesser amount of refrigerant will be forced to expand the same amount as the prescribed amount, which will make it cool more quickly. Airborne moisture will freeze as it comes in contact with the coil. This should be addressed by an HVAC professional.
  • Making your A/C work too hard.If you set the thermostat to a very cool temperature inside, at the same time as it's very hot outside, this can place an unreasonably high demand on the equipment. This can lower pressure in the system and result in freeze-up. Don't expect your A/C to work miracles during excessively hot weather.
  • Mechanical defects.Any number of mechanical problems can cause the indoor coil to freeze. These include a broke blower fan, a kinked refrigerant line, or a clogged filter dryer. This likely will require professional intervention.

If you can't fix your frozen A/C unit, contact your trusted HVAC professional. In the South Bay Peninsula and Santa Cruz, that's Valley Heating, Cooling, Electrical. Call us today at (408) 868-5500.

Our goal is to help educate our customers in the South Bay Peninsula and Santa Cruz areas of California about energy and home comfort issues (specific to HVAC systems).

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