Heat pump outdoor unit covered in ice

Symptoms

• Visible ice or frost coating the outdoor unit's coil or fan
• Ice doesn't seem to clear on its own over several hours
• Reduced heating performance alongside the ice

Likely causes

• CommonNormal light frost during cold, humid weatherSome frost is expected and clears automatically during periodic defrost cycles.
• CommonFailed defrost control board or sensorIf the system can't properly trigger defrost cycles, ice builds up unchecked.
• PossibleLow refrigerantReduced refrigerant can cause the coil to run too cold, leading to excess ice.
• PossibleOutdoor fan not running properlyWithout adequate airflow, ice can accumulate faster than normal defrost cycles can handle.
• Less commonUnit installed too low to the ground or blocked by snowSnow piling up around or under the unit can restrict airflow and worsen icing.

What to do

1. Clear away any snow piled around or under the outdoor unit, keeping at least a foot of clearance on all sides.
2. Watch for a normal defrost cycle: the outdoor fan may pause and you may see steam rising as ice melts, usually every 30–90 minutes in cold weather.
3. If ice has been building for several hours without any sign of a defrost cycle occurring, treat it as a fault rather than normal operation.
4. Don't chip or pick at the ice yourself, since this can damage the delicate coil fins.
5. Check that the outdoor fan is spinning freely and not blocked by ice itself.
6. Call an HVAC technician if ice keeps building without clearing, since the defrost control board or refrigerant level likely needs attention.

When to call a pro

Call an HVAC technician if ice on the outdoor unit doesn't clear through normal defrost cycles; the defrost control board or refrigerant level likely needs attention.

Safety