An evaporator coil freezes when too little warm air crosses it or refrigerant pressure drops too low. Common causes are a dirty filter, blocked returns, a failing blower, a dirty coil, or a refrigerant leak. Turn cooling off, run the fan to thaw it for a few hours, replace the filter, and request diagnosis if it refreezes.
Technical Consideration
How do I thaw a frozen coil safely?
Set the thermostat to Off for cooling and the fan to On. Place towels near the air handler for meltwater.
Thawing can take a few hours. Do not chip ice off the coil.
What airflow problems cause freezing?
Dirty filters, closed or blocked returns, a matted coil, or a blower running at the wrong speed.
Fixing airflow is often inexpensive.
When is it a refrigerant problem?
If airflow is good and the coil still freezes, low charge from a leak is likely.
A technician should find and repair the leak, not only add refrigerant.
Can running it frozen cause damage?
Yes. Liquid refrigerant returning to the compressor can damage it.
Stop running cooling until the cause is found.
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Local verification resources
Before authorizing work, use the Delaware license lookup. For projects that may require approval, consult the City of Wilmington permit information or the authority serving the property.