My HVAC System Froze In The Winter Weather… Now What?

Air Dynamics HVAC | #AirDynamicsCares | HVAC Frozen In Winter | Heat Pump

Estimated reading time: 9 minutes


Your heat pump is frozen; It’s Wintertime and you’re not sure what to do. First, check to ensure that your outdoor unit has proper airflow. Too much overgrowth or recent snowfall can impact your unit’s ability to breathe.

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Recent snowfall, overgrowth, or drifting snow can impede your unit’s airflow. Be sure to shovel the area around your outdoor unit and/or remove any overgrowth to ensure your outdoor unit has adequate airflow.

If you do not see anything blocking your unit’s room to breathe; don’t fret just yet. Although seeing your heat pump frozen on a cold day can be alarming; it is likely completely normal. So, how can you tell if the amount of ice buildup on your outdoor unit is normal or not? First and foremost, it’s important to understand how a heat pump works when it’s set to heating mode.


Contrary to what some may think, heat pumps do not create heat. Rather, they redistribute heat from the air or ground using a refrigerant that circulates between the air handler inside of your home and the outdoor compressor. The resulting heat can now be redistributed throughout your home. To understand how this works in more detail; check out the following video from This Old House on how a heat pump works in both heating & cooling modes. To see how a heat pump works in heating mode skip to 4:18 in the video below.

It is well known that heat pumps are versatile, highly efficient heating & cooling systems. Simply put, when your heat pump is in cooling mode, it absorbs the heat inside of your home and releases it outdoors. In heating mode, your heat pump will absorb heat from the ground or outside air (including cold air) and then release it indoors.


As mentioned above, when your heat pump has been operating in heating mode for a while; it is using a refrigerant to move the heat from outside of your home indoors. As the cool air makes its way outside it can create condensation.

The resulting condensation can then freeze on your coil as a result of cold outdoor weather. If your heat pump doesn’t defrost when it’s programmed to, it can prevent your heat pump from working properly. This is why it is important for your heat pump to switch to defrost mode every 30, 60, or 90 minutes. When your system is running in defrost mode, it will begin to blow warm air over the condenser coils inside of your outdoor unit. This process should take no more than 30 minutes to complete. You might even notice steam coming off of your outdoor unit as it goes through the defrosting process. This is completely normal and is not cause for concern.


Now that we have gone over how a heat pump works in both heating and cooling modes. We can better understand why frost/ice can easily accumulate on your heat pump on cold weather days. While this accumulation is completely normal as discussed, you should only see a thin layer of frost that does not cover your entire unit. This is a good indication that your heat pump is likely functioning as it should and will cycle through defrost on its own.

As noted by NACHI “a heat pump unit will defrost regularly when frost conditions occur. The defrost cycle should be long enough to melt the ice, and short enough to be energy-efficient.”

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However, there are some instances where a frozen heat pump could bring cause for concern indicating a problem with your unit. For instance, if you see a significant amount of frost/ice buildup covering your entire unit. This is a clear signal that your heat pump is not able to properly defrost on its own.

Not Cycling Through Defrost & Needs Service
Air Dynamics HVAC | #AirDynamicsCares | HVAC Frozen In Winter | Heat Pump
Fully Frozen Over Unit In Need Of Service

Your unit should never appear as though it’s trying to create its own personal snowman. If you step outside and see a large amount of ice buildup encapsulating your entire unit, you may have a more serious problem on your hands and it’s time to call in a professional like the ones at Air Dynamics HVAC. A trained qualified technician will be able to identify the underlying issue and address it in order to get your unit back to functioning as it was designed.


Your heat pump is designed to handle the possibility of ice buildup in cooler weather. In fact, your heat pump’s built-in defrost cycle is designed specifically to handle frost accumulation as a part of its normal operating cycle. This built-in defrost cycle will temporarily kick on in order to allow your unit to use the heat from the refrigerant to melt the frost/ice away. This process should only last an average of around 10-15 minutes.

Defrost mode usually lasts about 10-15 minutes, before the unit will start to heat again.

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While your unit is in defrost mode it will automatically switch into air conditioning mode for a short period of time until it unfreezes itself; at which point it will be able to return to functioning in heating mode once more. But don’t worry, you’re not likely to notice the difference. While all of this is happening, a backup heating cycle will automatically kick on. Keeping you and your family warm until it has finished. If however your unit is still frozen after 30 minutes and you feel the temperature dropping in your home; it’s time to consider calling a professional.


There are several things that can cause a heat pump to freeze unexpectedly. One of the most common causes is restricted airflow. This is why it is imperative to ensure your unit has adequate breathing room. Aside from simply ensuring that the area surrounding your outdoor HVAC unit is clear from snow and other debris. You should check your unit’s HVAC filter and ducts. Clogged air filters or debris can add to restricted airflow. Choking your unit of the air it needs to function properly. Without adequate airflow, ice can build up and cause your outdoor unit to freeze over.

Air Dynamics HVAC | Dirty Filter | Indoor Air Quality | #AirDynamicsCares |

Check your HVAC filters, and change them every 90 days as needed. This will help to keep your unit functioning as it should. Avoiding unexpected issues caused by restricted airflow.

Another thing you can do is to check your ducts for airflow. Do you feel air blowing from your vents when your unit is running? If not, then you may have a bad blower motor or other part that has gone bad on your unit. You should also check the fins on your outdoor unit. If you see any dirt or debris be sure to remove them.


When your HVAC unit freezes over it’s understandable that you may be worried. Especially if you’ve now determined that this is more than the normal ice/frost accumulation that your unit is prepared to handle. So, how do you unfreeze your HVAC unit when this happens? First, avoid the temptation to pour hot water over your unit or manually scrape away excess ice; we do not recommend this.

If your unit is fully frozen over, turn your unit off completely and contact a professional like the ones at Air Dynamics HVAC.

Air Dynamics HVAC | #AirDynamicsCares | HVAC Frozen In Winter | Heat Pump

Instead, turn your unit off completely and call in a professional. This will allow your unit to defrost on its own naturally while you wait for the technician to arrive. Avoid the temptation to speed up this process by scraping at the ice with a sharp object or taking any other means to speedily defrosit it on your own as these actions have the potential to cause unexpeted damage to your HVAC unit. As we mentioned earlier in this article; your unit should never look like the image above. This is not normal and is a clear signal that it’s time to call in help.


If you’re still struggling to get your HVAC unit to defrost on its own, contact a professional at Air Dynamics HVAC today. Our knowledgeable HVAC technicians can assist you in getting your heat pump back to functioning as it was designed.


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