Furnace AC Evaporator Coil Frozen — Causes and Fix

Published: July 23, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC

Why the Coil Freezes

The evaporator coil (sits on top of your furnace for AC) freezes when: airflow is restricted (dirty filter, closed registers, dirty coil), refrigerant level is low (leak), the outdoor temperature is too low for AC operation (below 15°C), or the blower is not running at full speed.

Emergency Steps

Turn off the AC at the thermostat but leave the fan set to ON — the fan will thaw the coil. Do not run the AC with a frozen coil — this can damage the compressor. Once the coil is thawed (2-4 hours), turn the AC back on and check for proper operation. If it freezes again, call for service.

Prevention

Change the air filter monthly during cooling season. Keep supply registers and return grilles open and unobstructed. Schedule annual AC maintenance to check refrigerant charge and coil condition. Do not run the AC when outdoor temperatures are below 15°C unless your system is designed for low-ambient operation.

Related Services

Safety Reminder

If you smell gas, suspect carbon monoxide or believe there is an immediate danger, leave the property and contact emergency services or the appropriate gas emergency authority. Do not remain inside — exit the building immediately and call for help from outside.