Why Your AC Freezes Up in Summer, and What to Do

An air conditioner freezes when the indoor coil gets colder than 32 degrees and moisture in the air turns to ice on it. The usual causes are restricted airflow, such as a clogged filter, closed vents or a failing blower, and a low refrigerant charge from a leak. If you see ice, switch the system from Cool to Off, run the fan only to help it thaw, check the filter and call for service. Do not chip at the ice.

The indoor coil, or evaporator, is where refrigerant absorbs heat from the air blowing across it. Normally the coil is cold, but warm air flowing over it keeps it above freezing, and the moisture it pulls from the air drains away as water. If too little warm air reaches the coil, or the refrigerant pressure drops too low, the coil gets colder than freezing. Moisture freezes on it, the ice blocks more airflow, and the problem feeds on itself.

Within hours, the coil and the copper line leading to the outdoor unit can be coated in ice, and the house stops cooling.

Restricted airflow is the most frequent cause. A clogged filter is the classic example, especially in a dusty Coachella Valley spring. Blocked return grilles, many closed supply vents, a dirty indoor coil, crushed or disconnected ducts and a weak blower motor can all have the same effect.

A low refrigerant charge is the other major cause. When there is less refrigerant in the system than it was designed for, the pressure in the indoor coil drops, and so does its temperature. A low charge always means a leak, because the system is sealed. See refrigerant leak repair for how leaks are found and fixed.

Turn the thermostat from Cool to Off, then set the fan to On so air keeps moving across the coil. That helps the ice melt faster. Check and replace the filter if it is dirty. Put towels around the indoor unit, because melting ice can overflow the drain pan. Thawing can take several hours.

Once the ice is gone, you can try cooling again, but if it freezes a second time, leave it off and call. Running a system that keeps freezing can damage the compressor.

The coil's fins and tubes are thin and easy to damage. Chipping or scraping ice can puncture a tube and create a refrigerant leak, which turns an airflow problem into a much bigger repair. Let it thaw on its own.

When a large block of ice melts, the drain pan and condensate line handle far more water than usual. If the line is partly blocked, water can spill into a closet, garage or ceiling. A technician checks the drain as part of the visit, and a spring AC tune-up keeps it clear.

Most freeze-ups are preventable. Change the filter on a regular schedule, more often in dusty months. Keep supply vents open and return grilles clear of furniture and boxes. Have the indoor coil and blower checked during a yearly service, and have any refrigerant leak found and repaired rather than topped up. Systems that run long hours in Indio's heat benefit most from that routine, because small airflow losses add up over a long season.

If your system has a history of freezing, mention it when you call. It helps the technician focus on airflow and charge from the start, and it often shortens the visit because the likely causes are already narrowed down.

A frozen coil is the system telling you something is wrong with airflow or charge. Fix the simple things, let it thaw, and if it happens again, have it checked before the compressor pays the price. For every service, see AC repair Indio.