Why Is My AC Compressor Covered in Ice?

It is a blazing 100-degree Texas afternoon, yet inside your outdoor AC unit, the heavy black compressor is completely encased in a solid block of thick, white ice. How is this possible during the hottest part of the year? A freezing AC unit is one of the most common—and most misunderstood—service calls we receive at SunDollar A/C & Heat.

An air conditioner freezing over is always a sign that the delicate balance of airflow and refrigerant pressure has been broken. The most frequent culprit is completely preventable: an extremely dirty, neglected indoor air filter. When the filter turns black and clogs, the indoor blower motor cannot pull enough warm return air across the freezing-cold indoor evaporator coil. Without that warm air acting as a heat source, the temperature of the coil plummets below freezing. The natural condensation forming on the aluminum fins instantly turns to ice.

Once the indoor coil freezes solid, the ice travels like a glacier straight down the copper suction line and directly into the outdoor compressor, leading to the shocking scenario pictured above. The other major cause of an ice block is a slow refrigerant leak. Low refrigerant levels cause the pressure within the system to drop abnormally low, which drastically drops the saturation temperature below the freezing point of water. If you ever notice ice forming on the copper pipes or the compressor, you must turn the thermostat setting to "OFF" immediately, turn the fan setting to "ON" to melt the ice, and call a professional. Allowing a compressor to run while frozen will ingest liquid slugging that will destroy the valves in seconds.