Heat Pump Outdoor Unit Frozen? Frost Is Normal, Ice Is Not

Heat pumps pull heat out of cold air, and the side effect is frost on the outdoor coil. The unit knows this and defrosts itself several times a day. So the question isn't "is there frost" — it's "is this the normal kind."

Safety first, every page: if you smell gas anywhere in the house, leave and call your gas company from outside.

Normal: a coating of frost that comes and goes

• A white, even frost on the coil fins on a cold, damp day.
• Every so often the outdoor fan stops, the unit makes a whoosh, and steam rises off it for a few minutes. Indoors, the air may go briefly cool. That's the defrost cycle — the unit is melting the frost on purpose.
• A wet spot or a small puddle under the unit afterward.

If that's what you're seeing, nothing is wrong. Don't intervene.

Not normal: a solid block of ice

• Ice so thick the fins are hidden, or the fan blades are frozen in place.
• Ice that's been there for days and never clears.
• Ice on the top of the unit over the fan, or a thick sheet up one side.
• The indoor air stays cold, or the house can't hold temperature.

That means defrost isn't keeping up, or isn't happening. Time to check.

What to check (no tools, no panels)

1. Turn it off. Set the thermostat to OFF, or to EM HEAT if the house is cold — that keeps you warm on the backup strips while the outdoor unit thaws. Running a frozen heat pump can damage the compressor.
2. Let it thaw on its own. Hours, maybe a full day if it's cold. Never chip at the ice — the fins bend and the coil punctures easily. Don't pour hot water — it refreezes into a worse block.
3. Look for what's dripping on it. A gutter overflowing or a downspout aimed at the unit will re-freeze it every night. Redirect the water.
4. Check the filter indoors. Restricted airflow makes the coil run colder than it should and can contribute to icing.
5. Clear the base. Snow packed around the bottom, or leaves blocking the drain holes, traps the defrost water where it refreezes. Keep 2 feet clear all around.

After it thaws

Switch back to HEAT and watch it over a day. If it frosts lightly and defrosts on schedule, you're done. If it turns back into a block within a day or two, the defrost control, a sensor, or the refrigerant charge is the problem — a technician fix.

When it's a pro

Re-freezing after a full thaw with the base clear and the filter clean; the outdoor fan not spinning even when thawed; or the unit humming without the fan. Call — and use EM HEAT in the meantime so the house stays warm.

Run the free troubleshooter first. It captures the ice pattern, the thaw result, and what you cleared, and gives you a summary to read to the dispatcher.

Related symptoms

• Heat pump not heating
• Emergency heat on the thermostat
• Ice on the AC line

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