Short answer
An AC freezes when the indoor coil gets too cold, usually because airflow is restricted by a dirty filter, closed vents or a failing blower, or because refrigerant is low from a leak. Turn cooling off and run the fan to thaw it, replace a dirty filter, and call if it freezes again.
How to thaw it safely
Thawing takes a few hours. Do not chip ice off the coil or lines.
- Set the thermostat to Off and the fan to On
- Put towels or a pan under the indoor unit for meltwater
- Replace the air filter if it is dirty
- Check that the condensate drain is not blocked
Why coils freeze
The indoor coil normally runs just above freezing. Anything that reduces warm air across it, or reduces the refrigerant in it, can push it below freezing so moisture turns to ice. Ice then blocks more airflow and the problem feeds itself.
- Dirty filter or blocked return grille
- Closed or blocked supply registers
- Weak or failing blower motor
- Dirty indoor coil
- Low refrigerant from a leak
- Running the AC on very cool nights
Not sure it is safe to keep running? A local technician can check it today.
Call NowWhen to call a technician
If the coil refreezes after a new filter and open vents, the cause is likely refrigerant or the blower. Refrigerant work requires EPA certification, and simply adding refrigerant without finding the leak only delays the next freeze.
Related questions
Will running the AC frozen damage it?
It can. Liquid refrigerant reaching the compressor and meltwater overflowing the drain pan are the main risks. Thaw it first.
How long does an AC take to thaw?
Often one to a few hours with the fan running, depending on how much ice built up.
Is ice on the outdoor unit normal?
Not in cooling mode. In heating mode, heat pumps frost up and defrost periodically, which is normal.
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HVAC troubleshooting in Fountain ValleyThis guide is general information for homeowners, not a diagnosis of your system. For anything involving gas, carbon monoxide, electricity or active leaks, stop and call a qualified professional.