Why is my AC freezing up?

The two root causes behind a frozen coil

The evaporator coil normally hovers just above freezing as refrigerant absorbs heat from household air. Anything that reduces the warm airflow across it, such as a packed filter, closed or blocked registers, a dirt-coated coil, or a weak blower motor, lets the coil temperature fall below freezing so humidity in the air ices onto it. The second path is low refrigerant: a leak drops system pressure, which drops the coil temperature, and the same icing follows. Running the AC on cool days, generally below about 62 degrees outside, can trigger it too.

How to thaw it without making things worse

• ✓Switch the thermostat from cool to off, but set the fan to on so warm air melts the ice faster
• ✓Replace the air filter while you wait
• ✓Open every supply register and clear furniture from return grilles
• ✓Check for water around the air handler and protect the area, since melting ice has to drain somewhere
• ✓Never chip or pry ice off the coil, because the fins and tubing damage easily

Why repeat freezing means a service call

If the system freezes again after a full thaw and a clean filter, the cause is almost certainly a refrigerant leak, a dirty evaporator coil, or a blower problem, none of which are homeowner-serviceable. Running a freezing system also floods liquid refrigerant back toward the compressor, risking the most expensive component in the unit. A technician can find and repair the leak, restore the correct charge, and clean the coil properly. PJ MAC HVAC repairs every major brand and has been doing this work for more than three decades.

Frozen solid at midnight in a heat wave? PJ MAC HVAC runs true 24-hour service, so help is a call away at any hour.