Heat Pump Freezing Up
Quick Answer
A light frost on your heat pump's outdoor unit is normal during heating season. However, if the unit is encased in thick ice, the defrost system has failed. Never pour hot water on it! This can crack the coils. Call for service if ice persists.
Safe Checks You Can Do
- 1Replace air filter - Restricted airflow can contribute to freezing problems.
- 2Clear debris - Remove snow, leaves, and debris. Maintain 2 feet of clearance around unit.
- 3Watch for defrost - The unit should defrost periodically. You'll see steam and hear clicking.
- 4Run cooling mode - Briefly running in COOL mode can melt ice, but don't do this if it's very cold.
Likely Causes
- Failed defrost control
The defrost timer or sensor may have failed, preventing the defrost cycle from running.
- Stuck reversing valve
The valve must switch to cooling mode for defrost. If stuck, defrost won't work.
- Low refrigerant
Low charge causes the outdoor coil to run colder than normal, leading to excess ice.
- Fan motor failure
If the outdoor fan isn't running, airflow is reduced and ice accumulates faster.
- Restricted airflow
Debris, fencing, or shrubs too close to the unit restrict airflow.
When to Call a Pro
- Ice covers most of the outdoor unit
- Defrost cycles aren't happening (watch for steam)
- Ice doesn't clear after 24 hours of normal operation
- The outdoor fan isn't running
- You hear unusual noises from the frozen unit
Related Symptoms