Why Is My Heat Pump Covered in Ice? A Portland Tech Explains

It’s normal for a little frost or ice to form on your heat pump during the winter months. Fortunately, your heat pump contains a defroster that helps melt any ice build-up.

You may have a problem, however, if ice covers your heat pump for longer than four hours.

Note: If you’ve determined that your heat pump isn’t defrosting and ice has covered your heat pump for 4+ hours, turn it off and call a technician. Do not attempt to chip ice off the unit as this can cause further damage.

In this blog, we’ll explain:

  • How heat pumps work (and why a little ice is normal)
  • How your heat pump’s defrost mode works
  • Issues that can cause excessive ice buildup

Rather talk to a heat pump repair professional? Contact Four Seasons to talk to a trustworthy, NATE-certified technician.

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How heat pumps work (and why a little ice is normal)

Heat pumps work by transferring heat from one area to another.

For example, in heating mode, your heat pump absorbs heat and transfers it into your house. In cooling mode, the heat pump moves heat out of your house.

More specifically, in heating mode, your heat pump uses refrigerant-filled coils to collect heat from the outside air (yes, there’s still heat in cold air). The heat collected by the coils then transfers to indoor air and the warm air is then pushed into your home.

Keep in mind that when in heating mode, your heat pump’s outdoor coils are colder than the surrounding air. That means that the warmer outdoor air will condense on the chilly coils. And, in cold temperatures, that condensation can turn into frost. As the warmer outside air continues to condense on the cold heat pump coils, frost/ice will build over time.

Fortunately, all heat pumps have a built-in “defrost mode” that melts any ice or frost that forms on the unit.

How your heat pump’s defrost mode works

In defrost mode, the heat pump reverses its operation and goes into cooling mode. The refrigerant-filled coils now absorb heat from the air inside your home then transfers that heat to the outside unit, where it quickly melts any frost/ice that has formed on the outside coils.

The defrost cycle should melt ice from the unit within five to ten minutes and then return to its regular heating mode.

Of course, if ice covers your heat pump longer than four hours, you likely have a problem with the heat pump’s defrost mode ... Let’s discuss the issues that can prevent defrosting.

Issues that cause ice build-up

Issue #1: A malfunctioning defrost control board

The defrost control board controls when and how often your heat pump goes into defrost mode.

Components that can malfunction and can cause excessive ice buildup include:

  • The defrost thermostat. A malfunctioning thermostat cannot detect cold temperatures and therefore won’t kickstart the defrost cycle.
  • The defrost timer. In normal operation, the timer should kickstart the defrost cycle after a certain time has passed and outside temperatures are still cold enough to cause frost buildup. A faulty timer may never kickstart the defrost cycle.
  • The reversing valve. The reversing valve reverses the flow of the refrigerant so that the outside coils heat up and melt the frost. If the reversing valve is stuck or broken, the outdoor coils will remain cold and frost will continue to build.

Issue #2: A malfunctioning blower motor

If your heat pump’s outside unit fan is malfunctioning, it won’t be able to pull outside air over the cold coils. Without the fan drawing in air, the heat pump can’t absorb as much heat from the outside air, which can cause the already cold coils to drop in temperature and cause ice buildup.

Some of the issues that can cause a blower motor to malfunction include:

  • Dirt or debris in the fan blades
  • Dirt or debris on the coils
  • A bad capacitor

Issue #3: Low levels of refrigerant

Low levels of refrigerant increase refrigerant pressure which results in colder-than-normal coils and inadequate heat circulation and causes the coils to freeze. Low refrigerant is the result of a leak that requires professional repair.

If your heat pump ices up in the summer

While it’s not unusual for your heat pump to ice up in the winter, it’s almost always a problem if ice forms on your heat pump in the summer.

A heat pump that’s icing up during warm weather is most commonly caused by:

  • A dirty evaporator coil
  • Low refrigerant levels

A unit that ices up in the summer will not cool efficiently. You can prevent this from happening by scheduling routine maintenance with a licensed technician who will keep your unit clean and monitor the refrigerant levels.

Want a trained heat pump professional to fix your heat pump?

When you choose Four Seasons, you will always get an honest recommendation, a fair estimate and exceptional service during every step of your heat pump repair.

Our NATE-certified HVAC professionals will thoroughly inspect your heat pump to determine why it’s icing up.

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