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Subscribe to our RSS Feed A Heat Pump Will Sometimes Frost Over — How and Why That Happens

Thursday, January 22, 2015

Dealing with a frosty heat pump this winter? It’s a common problem in colder climates and one that can impact your home’s overall comfort. Knowing the hows and whys of heat pump freezing can help you understand your unit better and keep your Chicago area home out of the cold.

What's Normal and What's Not

When in heating mode, the average heat pump transfers the latent heat found outside and expels it indoors. In short, it operates just like an air conditioner, only in reverse. Reversing valves on the unit help switch it from absorbing and transferring heat out of your home to bringing said heat into your home.

For this reason, it's perfectly normal for a heat pump to be covered with a light coating of frost or even a light sheen of ice during chilly weather. The heat pump will take care of this by using its defrost mode, which essentially heats up the outdoor condenser coil enough to melt the frost and ice.

What isn't normal is seeing a heat pump encased in large sheets of ice. There are several reasons why that could happen and plenty of ways you can correct those issues.

Why a Frosty Heat Pump Happens

A frosty heat pump happens for a wide variety of reasons, including:

  • Lack of airflow caused by a faulty outdoor fan motor or air flow blockage
  • Faulty defrost relay, thermostat or sensor
  • Condensation and ice draining issues, especially if the unit itself has sunken into the ground
  • Low refrigerant charge, which can change the amount of pressure required for proper heat transfer
  • Faulty reversing valve or solenoid coil
  • Freezing rain or leaky gutters introducing freezing water over the unit

What You Can Do

Preventing a frosty heat pump is sometimes as simple as cleaning up surrounding debris or protecting it from water run-off from the roof. In other cases, leaving the unit on defrost or just leaving it off for a while may help de-ice it. For problems requiring replacement parts, you're better off calling your trusted HVAC technician.

For professional help with a frosty heat pump, or for other home comfort concerns, contact

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