What Makes A Heat Pump Unit Freeze Up?

A heat pump system works by circulating refrigerant to draw warmth out of the outside air in the heating season and bring it inside. Then, in the cooling season, it draws the warmth out of the inside air and disperses it outside. The refrigerant makes a heat differential between the outside coils and the air around them. This is why it’s pretty normal for your heat pump to freeze up every now and then. The system corrects this by switching to cooling mode so that warmth is transferred to the coils to defrost them, why a backup heating system keeps the inside warm.

But sometimes the problem goes further, and while there are some steps you can take at home to troubleshoot and correct the problem, there are some issues that require an HVAC technician. Here are some things to look out for that will need professional attention.

What you can do at home

If there’s not enough airflow over the coils, they can develop ice beyond what it would get in normal operation. You can help prevent this by keeping the space around the unit clear of furniture, appliances, plants, snow, or debris. Make sure the supply and exhaust ducts are likewise clear. Clean or replace the air filter regularly, and make sure the roof or gutter are not dripping water onto the unit.

What you need a professional for


Low refrigerant levels could prevent the defrost cycle from working, as the refrigerant is what carries warmth to the coils. Not enough of it might mean the coils won’t get warm enough to clear the frost and ice.

Defrost controls

The controls, sensors, and thermostats of the defrost cycle could malfunction which will lead to preventing the cycle itself. This, unfortunately, isn’t something that is a simple DIY fix and will require professional care.

Reversing valve

The reversing valve is the component that switches the whole system from heating to cooling and vice-versa. If it sticks and won’t move, the defrost cycle won’t start.

Fan motors

The condenser works in tandem with the fan that forces air over it. If the fans are damaged or their motors are malfunctioning, the system won’t operate properly and may build up ice.


The outside unit is set up on a small concrete slab. That slab might settle a little over time, but if it settles in just the wrong way, it might start pooling water that will freeze and possibly encourage more freezing. Even if it doesn’t freeze anything else, it will cool the air around it and possibly reduce the efficiency of the system.


While you should do what you can to keep large amounts of snow off the unit, the elements might sometimes move too fast for you. A nightlong storm of freezing rain could coat your coils in ice before you get up. And if there’s too much for the defrost cycle to handle, it would be smarter to call a technician than to chip it off yourself.

These problems will require a technician because heat pump repair has too much risk as a DIY project. You would have to connect all the wires correctly, fit all the parts properly, and correctly estimate the amount of refrigerant for the right pressure. Too much can go wrong. So, unless the issue can be fixed with the basic steps we mentioned above, call your local HVAC professionals.

Twin Air, LLC is a family-owned HVAC business in Manassas. We have more two decades of experience in serving the Northern Virginia area. If your heat pump system is freezing up and you’ve tried the proper at-home steps, give us a call at (703) 754-1062 or contact us on our website.


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