Short answer
AC coils freeze when too little warm air passes over them (dirty filter, closed vents, weak blower) or the refrigerant charge is low from a leak. Turn cooling off, run the fan to thaw, replace the filter, and call a tech if it freezes again.
Thaw it safely
Set the thermostat to Off and fan to On. Thawing takes 1–3 hours. Put towels near the air handler, since melting ice can overflow the pan.
Common causes
Airflow and charge account for almost every frozen coil.
- Dirty filter or coil
- Closed or blocked supply registers
- Failing blower motor or capacitor
- Low refrigerant from a leak
- Running the AC on cool nights below about 60°F outdoors
What the tech checks
Static pressure and blower operation for airflow, then superheat and subcooling for the refrigerant charge. If it's low, the leak should be found and repaired.
Questions
Is it safe to chip ice off the coil?+
No. The fins and tubes are thin and easily punctured. Let it melt.
Editorial note: this guide is general information for homeowners, not a diagnosis. Desertline Heating & Air is a referral service; a licensed contractor should inspect your equipment before repairs.