Solutions for a Heat Pump Icing Up During Winter

By | October 12, 2023

Solutions For a Heat Pump Icing Up During Winter
Heat pumps can ice up when it is very cold outside and have a certain frost covering them.

While some ice is normal, something is wrong if the entire unit is encased in ice and frozen solid.

Air must pass between the fins of the outdoor unit to work correctly.
Heat Pump Freezing Up
If the condensing fan motor cannot pull air in and out through the fins, there is a problem.

Why Does a Heat Pump Freeze Up?

A heat pump freezes up when the temperature drops below its operational rating, or it has malfunctioned.

While Heat pumps are becoming much more efficient every year, they each have a set low temperature at which they can work and not freeze up.

If the temperature becomes too cold, a heat pump will temporally go into defrost mode to melt the ice.
Heat Pump Icing Up During Winter
Defrost mode switches the heat pump into air conditioning mode (yes, air conditioning) for a short time until it unfreezes itself and can go back into heat mode.

Defrost mode usually lasts only 10-15 minutes. While a unit is in defrost mode, supplemental heat, usually heat strips, kicks on to keep the air warm.

Heat strips are large elements that work like a big space heater, by using electricity to heat the elements up and send out heat.

Heating a home with heat strips is terribly inefficient and not designed to be on for long periods. However, if they are used a lot, the cost will show up on an electricity bill.

How Do You Unfreeze a Heat Pump in the Winter?

The heat pump should melt and unfreeze the outside condenser automatically by temporarily going into air conditioner mode.

This is called defrost mode, and the heat pump will blow out cold air while it defrosts the unit.
Heat Pump Icing Up During Winter 2
Defrost mode usually lasts 5-10 minutes, and then the unit will start to heat again.

In very cold weather, the unit may go into a constant heat and then defrost mode cycle.

What to Check When a Heat Pump is Freezing Up

  • Check if the air filter is dirty and replace it. Airflow is a must for a heat pump to work correctly.
  • Does any air blow from the vents at all? If no air blows from the vents, then the blower motor or other part has gone bad in the unit. A quick way to test this is to manually set the thermostat to Fan Only mode and see if any air blows from the vents.
  • When a heat pump runs, the large fan on the outdoor unit (called the condensing fan motor) should kick on at some point and blow air out through the outside unit fins.
  • Check the outside unit fins for any debris that may be blocking air from passing through, such as dirt or leaves.

What Does it Mean When a Heat Pump Freezes Up?

A heat pump will freeze up when the outside weather becomes too cold for the unit to operate or it has malfunctioned and needs repair.

Each unit has a different low temperature that was designed to operate and will begin to freeze when the temperature drops below this.

If it is very cold outside, the unit likely will go into defrost mode and start to heat again when done.

If the temperature is above 32 degrees Fahrenheit and the unit is freezing up, there likely is a malfunction and may have low refrigerant or a bad component.

The outside unit on a heat pump will freeze up if the temperature is too cold.

How efficient a unit is will depend on how low a temperature it can work without icing up.

Some heat pumps are designed to work in very cold temperatures, while others do not so much.

A water hose can be used to melt the ice buildup if needed, but don’t use salt or any other abrasive, as this will only cause corrosion of the unit.

If the unit is frozen solid but still blowing hot air, more than likely, the heat strips have activated and are heating the home.

Heat strips will quickly run up an electricity bill and be expensive if done long-term. A day or two may not be that bad, but weeks or a whole month of heating a home this way will definitely be
noticeable. If this is the case, call out a repairman as soon as possible.

Category: Heat Pump HVAC how to

About Aaron H. Benetti

Aaron H. Benetti an HVAC technician who has worked in the field since 1991. He began his career as an HVAC installer and later began doing troubleshooting and repairs. Around 2010, he began to write books on HVAC topics, mainly tutorials and how-to information. Currently, Aaron works as an HVAC tech and also writes many articles and posts for websites as well as books and videos on HVAC topics.

2 thoughts on “Solutions for a Heat Pump Icing Up During Winter

  1. Inland Empire Comfort

    Absolutely! If your heat pump is blocked by ice or doesn’t seem to be defrosting enough to allow it to run normally, there are a few things you can check. Make sure that the air filter is in good condition. Replace the filter if it seems to be full of buildup.

  2. Sidney

    I had a problem with a Lennox. Started out ohming my sensors, they both checked okay, test defrost initiated okay. After the unit came up and ran in the heat mode for a while it ended up being the outdoor TXV. It had dropped my pressure down and put the board in a low pressure lockout. Homeowner would have never had a clue it was happening but it was 77° yesterday (broke a record high) and they turned on the AC and it never cooled the house down. That’s when they went out back and noticed the ODU wasn’t running. It’s surprising that Infinity didn’t trip out on some kind of fault. I’ve always hated that style of package unit and what a terrible idea putting those control boards inside of the blower compartment.


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