Steam rising from a heat pump outdoors on a cold morning is usually normal. The unit is melting frost off its coil in a defrost cycle. Ice that stays thick and does not clear is not normal. Turn the unit off and call a licensed pro. Climate Pros Tucson can match you with one.

Why does a heat pump steam in winter?

It steams because it is clearing frost. In heating mode the outdoor coil gets cold and can collect frost. The unit briefly reverses, melts the frost, and the warm coil turns the water to vapor. Fans may stop for a few minutes, and the indoor air may feel cooler during that time.

Tucson’s winters are mild, so this is occasional. The airport averages fewer than 12 nights a year at or below 32F, and the City of Tucson lists a winter design temperature of 35F. A heat pump is the sensible default for a Tucson-basin home. On a clear, cold, damp morning, expect to see some steam.

When is ice a problem?

It is a problem when ice builds up and stays. Signs include a coil wrapped in ice, ice on the lines, or the unit sitting iced for a long stretch with weak heating indoors. That can point to a stuck defrost cycle, a failing sensor or reversing valve, low refrigerant, restricted airflow or a dirty coil.

  1. Look at the unit from a safe distance. Do not chip ice with tools, since you can puncture the coil.
  2. Check that leaves, debris or a cover are not blocking airflow around it.
  3. Check the indoor air filter. See heat pump not heating in Tucson.
  4. If ice stays, turn the unit off at the thermostat and call a pro.

A frozen unit in summer is a different problem. See AC freezing up.

What about Mount Lemmon and Summerhaven?

Colder places behave differently. Mount Lemmon and Summerhaven are far colder than the basin, with about 53 nights a year at or below 32F against fewer than 12 at the airport. There, a cold-climate heat pump or backup heat is a question for the pro, not a default. See HVAC in Mount Lemmon and Summerhaven.

What should you ask the pro?

Ask whether the defrost controls and reversing valve were tested, and whether airflow and the coil were checked. See heat pump reversing valve and heat pump maintenance in Tucson. Check any contractor’s license at roc.az.gov. See heat pump service and the Tucson HVAC hub.

When the ice won’t clear

Call (520) 353-2520 and we’ll match you with a licensed local pro.