Heat Pump Freezing Up – Troubleshooting and Repair Tips

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A frozen heat pump is a commonly occurring problem in HVAC units. While it usually happens during winter, heat pumps could freeze up during summer too. Such heat pump issues occur due to different reasons, some of them easier to fix than others. This article will discuss why a heat pump freezes up and how to troubleshoot it.

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Why is my heat pump freezing up?

Most reasons for heat pumps freezing up vary from weather-related reasons to internal causes. In less serious cases, the defrost cycle usually kicks in as programmed, so there would be nothing to worry about. But if it doesn’t, that’s where you should start examining the heat pump.

We’ll briefly tackle the season-related problems before discussing more general reasons. Some of these general causes might need professional maintenance. Not to worry as there are problems you can still troubleshoot by yourself.

What is a defrost cycle

A defrost cycle is one of the three cycles of a heat pump. The other two are heating and cooling. If you would like to know more about how does the heat pump work, check out this article.

When the outside temperature drops below 30 F, the moisture in the air freezes on the heat pump exchanger. Once the sensor measures the low temperature, the unit goes into the defrost cycle automatically.

The reversing valve activates and runs the refrigerant backward, extracting heat from the house and delivering hot refrigerant to the outdoor coil melting ice and defrosting the system.

It is easy to recognize when the system goes into the defrost cycle. Heating stops, indoor and outdoor fans also stop running while the compressor keeps operating. The unit can be in a defrost cycle of up to 10 min.

Keep in mind that each time the defrost cycle begins, a supplemental heating system activates to keep an inside temperature stable.

If the ice is not removed, the efficiency gets lower, or even worse, some of the elements get damaged.

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Winter-related problems

During winter, it’s typical for frost and snow to gather on the unit. If the unit stops working, however, you need to check on the outdoor unit. DO NOT pick on the ice with sharp objects. Hose it down with water if you can (and weather permitted) to avoid damaging the parts of the heat pump, such as the coils and fins.

Here are some possible causes for your heat pump freezing in winter.

Clogged or dirty coils

Dirty or clogged up coils are a common reason for your heat pump getting frozen. Dirt, snow, and other debris could be blocking the evaporator and condenser coils. This might hinder air from properly flowing through the unit, preventing other functions from working, such as the defrost cycle.

Cleaning the coils is a good first step to keep this from happening. You may also want to clear the surrounding area of the outdoor unit. Clear any snow and vegetation that could be affecting the proper work of the outdoor unit.

Dripping gutter water and freezing rain

Any water on the heat pumps during the cold weather can cause your heat pump to freeze up. Water dripping and gathering on your unit could most likely come from freezing rain. If not freezing rain, the moisture could come from leaking gutters and the roof. If too much moisture gathers on top of the unit, it will eventually freeze up the sensitive elements, if not attended to immediately.

That is why the correctly selected location of the heat pump is essential. As much as possible, heat pumps should be installed away from gutters. But if it can’t be helped, repair the gutter if it’s starting to leak on your heat pump or build a shelter for the unit.

Unstable grounding

Water does not only come from above. Your heat pump could sink into the ground (settling) if it is not supported correctly. Like gutter water and freezing rain, water from below or standing groundwater could also be the cause of the unit freezing up. This water usually comes from moisture in your unit that has not drained off properly. You can contact your local technician to help you level the outdoor unit as it should be.

Heat pump concrete slabs should be at least a few inches above the ground surface.

These are some of the common, fixable causes. Most of these repair methods usually just involve proper and regular maintenance. The same goes for summertime problems though the causes and troubleshooting are still slightly different.

Summer-related problems

Even in hot weather, heat pumps can still freeze up while cooling your home. Some of these summertime heat pump problems can be fixed on your own in less serious cases. Here are some common causes and problems for heat pumps freezing up during summer.

Poor airflow from dirty components

Like winter-related problems, lack of proper airflow could also freeze your unit in the summertime. Your unit most likely has a dirty filter or dirty coils, including faulty blower and blocked return vents. Air will not flow properly if these components are blocked, making the coils colder than usual.

Cleaning them should do the trick. For air filters, make sure to clean them regularly, and doing it every six weeks should be good enough. Wiping or washing them should do unless they’re damaged, then you should replace the filters. The coils might be a little harder to reach for which you might need the help of a technician.

To keep this from happening, clear the outdoor unit of any nearby vegetation and debris. You should also check the heat pump’s air filters every 4 to 6 weeks at best.

Poor thermostat settings

Just like many heat pump problems apart from freezing, the problem might be in the thermostat. One problem could be is that the temperature is set too low. There’s a quick fix for this using the thermostat, especially if your heat pump has a defrost cycle.

You can wait for 30 to 45 minutes to see if the defrost cycle has kicked in. Set the system to fan mode or heat mode to reverse the process. The heat from your home should be able to defrost the coils in your heat pump.

Blocked or closed vents

Dirty filters and coils are not the only reason for poor airflow. The vents are either closed or blocked if the vents are the problem. Keeping the vents open in only one room will limit the warm air flowing in the coils, eventually freezing them. Always keep the vents open in all areas of the house to keep free airflow. On the other hand, if the vents are dirty, make sure to get an HVAC technician to help clean them up.

These are some of the causes of heat pumps freezing up in summer. Like the winter problems above, you can fix some of these problems by yourself. However, if these are not the causes, the problem might be something more serious.

Other causes

Not all causes for frozen heat pumps can be fixed alone. Here’s a quick rundown of other serious causes for frozen heat pumps that are common for both seasons:

  • Refrigerant leaks – if your unit is running low on refrigerant, the heat pump will deal with the low pressure so it might not be able to transfer heat properly.
  • Broken reversing valve – this determines the flow of the refrigerant. If the refrigerant is fine, but the heat pump still froze over, check the valves.
  • Faulty thermostat – your heat pump might not be pulling the right amount of heat due to the thermostat. If the heat pump still does not work after multiple thermostat adjustment, it needs to be replaced.
  • Insufficient fan speed – the fan must blow air at the proper speed and over the evaporator coil.
  • Issues with the fan motor.
  • Wiring problems.

These are some more problems that might cause a heat pump to freeze over. For these cases, you need to call your local HVAC repair to fix these problems.

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Maintenance tips

Proper and regular maintenance of the unit always goes a long way to preventing problems from occurring, and the same goes for frozen heat pumps. Here are some tips you can keep in mind both for maintenance and troubleshooting.

Always keep the unit and its surroundings clean. This is a very common cause of HVAC breakdowns. Keep the unit’s area clear of vegetation and debris.

Clean or replace the filter as often as needed. Cleaning the filter every six weeks is good enough. Replace the filter is if it’s damaged or uncleanable.

Regularly check all the components of the unit for leaks or any other damage it might have sustained.


These are some of the tips you can adopt to keep your unit from freezing over. Keep in mind that it is normal for the outer evaporator coils to get cool during heating, but it is not normal to have the whole unit covered in ice for a long period of time, or have a thick layer of frost/ice.

As the frozen evaporator coil of heat pumps and air conditioners is one of the most common problems during the cooling process, regular maintenance before the hot summer is your best choice. 

If you feel there are problems you can’t find on your own, contact the local maintenance just to be sure.


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