Why Do Air Handlers Freeze Up in Central AC Units?

Anne C. Watkins

Frozen air handlers are signs of serious problems in a central air conditioning unit. Several issues cause ice to form on air handlers, which can result in a failure to produce cool air or damage to the entire unit.

Problems with the Indoor Fan Unit

A working unit should send cold air through the vents.

The fan inside the unit should be blowing. If there are problems with the wiring or the breaker, the fan will not run and the unit will freeze up. If the fan is blowing correctly, something else is causing the freezing.

Clogged Air Filters

Air filters should be clean, dust-free and properly installed. Poor airflow contributes to freezing and can be remedied by replacing the clogged air filter with a new one. Be sure that nothing is blocking the area around the filter and preventing proper air flow.

Low Refrigerant Levels

When refrigerant levels drop too low the air handler freezes. Levels 1 to 2 pounds low can impact the unit's performance. It may still run but will not cool. Once the coils have frozen, continued operation of the air conditioning system can result in damage to the unit.