Fix it
Why is my heat pump icing over?
A light frost coat that comes and goes is a heat pump working normally in winter. A unit encased in ice that never clears is a defrost failure — and running it that way can bend the fan into the coil.
What it usually is
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Normal frost and a working defrost cycle
Below about 40°F the outdoor coil runs colder than the air and collects frost; every 30 to 90 minutes the unit reverses briefly, steams dramatically, and clears itself. Steam is not smoke — this is the machine doing its job.
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A failed defrost sensor or control board
If defrost never triggers, ice builds until airflow stops. Thick, persistent ice on the whole coil after a mild day is the giveaway.
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Low refrigerant running the coil too cold
An undercharged system frosts even in mild weather and heats poorly at the same time. This one needs gauges, and the leak matters more than the top-up.
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Blocked airflow or water dripping onto the unit
Leaves against the coil, a fence too close, or roof runoff dripping onto the cabinet all build ice faster than defrost can shed it.
What you can check yourself
Clear debris and snow from around the unit and confirm nothing drips onto it from above. Watch one defrost cycle: reversal, steam, clear coil within ten minutes is a pass. Never chip ice off the coil — fins bend and the damage outlasts the winter. A gentle rinse with a hose on a mild day is the safe manual assist.
When it’s a job for a pro
No defrost within a couple of hours of visible icing, or icing in mild weather, means sensor, board or charge diagnosis. Shut the unit to OFF (use auxiliary heat) if ice reaches the fan blades.
Defrost sensor or board repairs typically run $200 to $650; refrigerant diagnosis and leak repair varies more widely, commonly $300 to $1,000.
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