Heat Pump Freezing Up? Here’s What to Do

In the cold winter months, a thin layer of ice may form on the coils of your heat pump. Don’t worry! That’s completely normal.

However, if an excessive amount of ice starts accumulating on your heat pump, something is wrong.

In this article, I’ll go over what you need to do if your heat pump is freezing up. I’ll also explain how a heat pump’s defrost cycle works and how to manually defrost your heat pump so you can get your home warm and toasty again.

What to do when your heat pump is freezing up

If your heat pump is freezing up, the first thing that you need to do is turn it off.

Next, take a look at the air filter on the indoor unit. A dirty air filter can cause airflow restrictions that lead to frost build-up on the heat pump outside. If the air filter is dirty, remove the air filter, clean it, and reinstall it.

Check the heat pump outside and see if there are any nearby sources of moisture that are contributing to the frost build-up. A leaky water hose or rain gutter near the heat pump can sometimes cause excess frost to build up on a heat pump. Take some time to patch up any leaks so that there is no moisture near your heat pump.

If your heat pump has a defrost cycle that you can start manually, turn your heat pump back on and engage the manual defrost cycle. 

If you complete the above steps and your heat pump is still freezing up, then it could be due to one of the reasons below:

  • The outdoor unit’s fan motor is malfunctioning or broken.

  • The outdoor unit’s fan blades are dirty, warped, or broken.

  • A sensing element in the outdoor unit, such as a thermostat, frost sensor, or refrigerant metering device is broken.

  • There is a refrigerant leak in the system.

  • The reversing valve is malfunctioning.

In any of the above situations, it’s best to call your local HVAC professional to troubleshoot the issue. 

If you need to manually defrost your heat pump to quickly get it up and running, check out my instructions below.

How does the heat pump defrost cycle work?

The heat pump defrost cycle works by sensing when there is frost build up on the outdoor unit. When the frost sensor triggers, the heat pump’s reversing valve engages, and the heat pump goes into defrost mode.

While in defrost mode, the heat pump operates like an air conditioner—the outdoor coil gets hot. This is known as reverse cycle defrosting (RCD). 

During the defrost period, hot gas is pumped into the outdoor coil to melt away the frost. The heat pump runs like this for a few minutes until all the frost melts away.

After the frost melts away, the frost sensor resets and the heat pump returns to normal heating operation.

Will emergency heat defrost a heat pump?

Turning on the emergency heat will not help defrost your heat pump. The emergency heat setting on your heat pump provides heat to your home, it does not heat up the outdoor unit of your heat pump.

Most heat pumps come with a two-part system: the primary heat pump, and the secondary/emergency source of heat. Typically the emergency source of heat is an electric resistance strip heater, however some systems utilize gas, oil, or hot water heating as an emergency heat source.

The emergency heat source is designed to be used when the outdoor air temperatures are too cold to run the heat pump. Typically, a heat pump will shut off when outdoor temperatures dip below 25°-30° F, but some newer heat pumps can operate in temperatures below 0° F. After the heat pump shuts off, then the backup heating system will engage and keep your home at a comfortable temperature.

If your heat pump’s normal defrost cycle is not working, then you will need to defrost your heat pump manually to get it running again. 

How to defrost a heat pump manually

If you need to defrost your heat pump manually, follow these steps:

  • Turn off the power to your heat pump at the disconnect or circuit breaker.

  • If there are large, loose chunks of ice on your heat pump, these can be removed by hand. DO NOT use tools to chip away ice from your heat pump—this could result in damage.

  • Using a garden hose, spray water at the frosted parts on the heat pump to remove the frost.

  • If there is frost buildup on the interior of coils, you may need to open the top of the heat pump outdoor unit to access the inside of the unit. Remove the top cover and fan from the heat pump to gain access to the interior of the unit and spray it down with water to remove the frost.

  • After the frost is removed, reassemble the heat pump. Inspect the electrical parts of the heat pump to ensure that they didn’t get wet while defrosting the heat pump. If the electrical parts are wet, let them dry first before turning the power back on.

  • If everything looks good, go ahead and turn the power to the heat pump back on!

If you don’t have a garden hose to spray down your heat pump, then you can use a heat gun or blow dryer to melt off the ice. However, using a heat gun or blow dryer to remove frost will be much slower than using a garden hose.

After removing the frost from your heat pump, you’ll need to figure out why your heat pump got frosted up in the first place. 

Take a look around your heat pump for any signs of moisture, such as a leaky faucet or rain gutter. Sources of moisture around your heat pump will cause it to frost up.

Another common cause of a frosted heat pump is a faulty frost sensor. The frost sensor is a sensor that’s attached to the inside of the coil on the heat pump.

The frost sensor detects when there is a frost buildup on the coil. When it detects frost, it lets the heat pump know to enter the defrost cycle.

If you need a visual guide, check out this video below from Anthony Hoekstra on how to defrost an iced up heat pump: