A heat pump freezing up is caused by blocked airflow, low refrigerant, or a defrost cycle failure. Turn the unit off immediately and switch to fan-only mode to begin thawing. If the unit refreezes, call a licensed technician — running a frozen heat pump can damage the compressor.
Why Is My Heat Pump Freezing Up?
Normal vs. Abnormal Frost
Some frost on the outdoor coils during cold weather (below 40°F) is completely normal. Heat pumps have an automatic defrost cycle to handle this. The problem is when ice builds up significantly — covering the entire coil or the refrigerant lines.
Causes of Excessive Ice Buildup
- Clogged air filter — restricted airflow prevents proper heat exchange. Check and replace your filter first.
- Blocked outdoor coils — leaves, debris, or snow blocking the outdoor unit reduces airflow.
- Low refrigerant — a refrigerant leak causes the coils to run too cold. This requires an EPA-licensed technician.
- Defrost cycle failure — a faulty defrost board, sensor, or relay can prevent the unit from defrosting itself.
- Fan motor failure — if the outdoor fan isn’t running, heat exchange stops and ice builds up.
What to Do When Your Heat Pump Is Frozen
- Turn the system off at the thermostat to stop the compressor.
- Switch to fan-only mode to run warm air over the coils and help them thaw.
- Check the air filter — replace it if it’s clogged.
- Clear debris from around the outdoor unit.
- Wait 1–2 hours and check if the ice has melted.
- If the unit refreezes or ice is severe, call a technician immediately.
Why is my heat pump freezing up?
Heat pumps freeze due to blocked airflow (dirty filter or coils), low refrigerant charge, or a malfunctioning defrost cycle. A small amount of frost in cold weather is normal, but solid ice buildup is not.
What should I do if my heat pump is iced over?
Turn the heat pump off and switch to fan-only mode to thaw the ice. Do not chip or scrape ice off the coils. If it refreezes within an hour, call a technician.
Can a frozen heat pump damage the compressor?
Yes. Running a heat pump with severely iced coils can burn out the compressor — the most expensive component to replace ($600–$1,200+). Turn the unit off and get it serviced promptly.