Heat Pump Frozen? What's Normal and What Needs a Tech

What you're seeing

• Light frost that clears every so often: normal.
• Steam coming off the unit during defrost: normal.
• Thick ice covering the coil, the top, or the fan: not normal.
• Heat in the house getting weaker and the electric bill climbing.

How to track it down

Work through these in order, or follow along in the video above. Each step rules something out before you spend money on parts.

1. Check that it's actually defrosting

   During defrost the outdoor fan stops and you'll often see steam. If the unit never goes into defrost, look at the defrost board, the defrost sensor, and the reversing valve.

2. Look at the outdoor fan

   If the fan isn't running in heating mode, the coil will ice fast. Check the fan motor and its capacitor.

3. Check the outdoor coil

   A coil packed with dirt, leaves, or cottonwood runs colder and frosts faster. Clean it and make sure nothing is blocking airflow around the unit.

4. Check the charge

   A heat pump that's low on refrigerant runs a colder outdoor coil and ices up faster. This takes gauges and a tech who knows the heating-mode charging method.

5. Check where the water goes

   Gutters dripping on the unit, or a unit sitting too low in snow or standing water, can refreeze melted ice. Units should sit up off the ground so defrost water can drain.

If you're a homeowner

Don't chip at the ice. The coil fins are thin and easy to puncture. If the unit is solid ice, switch the thermostat to emergency heat so the house stays warm, and call a tech. With the power off, you can melt ice off with a garden hose. Never use a sharp tool or hot water from a kettle.