AC Frozen Coil (Evaporator Icing Up)

Without enough warm air flowing across the evaporator coil, the refrigerant inside drops below freezing. Moisture condenses on the coil and freezes into ice. Within hours, the coil is encased in a solid ice block.

Pull the air filter. Heavily soiled = found it. Also check for closed vents, blocked return grilles, or pets blocking airflow.

Less refrigerant = lower pressure = lower boiling point. The coil temperature drops below freezing. Moisture condenses and freezes. Repeated freezing despite fresh filter = strong sign of low charge.

Replace filter and let system thaw. If it freezes again within 24-48 hours, refrigerant is likely low. EPA-certified tech can confirm with pressure gauges.

If the blower motor is failing — running slow, fan blade clogged with dust, or capacitor weakening — airflow drops below the minimum needed to prevent freezing.

Hold your hand at a supply vent. Air should be strong and consistent. Weak flow with a clean filter = blower problem. Listen for motor whining, grinding, or running rough.

Closing supply registers ("to save energy") or blocking the return grille with furniture restricts airflow. The system loses enough flow to freeze the coil.

Walk through the house. Are any registers closed or covered by rugs? Is furniture pressed against the return grille (usually large, near floor or ceiling)?

Running AC when outdoor temps drop below 60°F can cause coil freezing. Common when people use AC overnight in shoulder seasons or for dehumidification on cool damp days.

Did you run AC overnight when outdoor temps were below 60°F? Or all day on a 65°F cool damp day?