5 Reasons Your HVAC System Is Freezing Up

February 15, 2023
Furnace in Nacogdoches, TX

Having an air conditioner or a heat pump that keeps freezing up can be quite annoying because the system won’t provide any cooling until it can thaw out. Your heat pump can also freeze up when heating during the winter. If your HVAC system does ever freeze, you will want to shut it off immediately. If the system keeps running, more and more ice will continue to build, and nothing can thaw until the system is off. Not only that, but running an AC or heat pump when it’s frozen can also burn out the compressor motor and force you to replace your outdoor unit. Air conditioners and heat pumps can freeze up for a few different reasons.

1. Clogged Air Filter

By far the most common reason that an HVAC system will freeze up is due to an air filter that is clogged from not being replaced often enough; this is the first thing to look for if your system freezes up. If you don’t replace your air filter at least every one to three months, it will eventually collect so much dust, hair, and debris that it will completely clog up. All of that debris built up on the filter will make it so that very little air can flow through it, and this lack of airflow can cause ice to start to form on the evaporator coil.

When your AC or heat pump is cooling, the blower draws warm air in through your return air vents and forces this air over the evaporator coil. Inside the coil is a cold refrigerant liquid that captures heat from the air so that the air blowing out of your vents is much cooler than the air being drawn into the system. If there isn’t enough warm air coming in, the refrigerant will stay too cold, and the condensation that naturally forms on the coil will start to freeze.

2. Closed or Obstructed Return Air Vents

If your return air vents are closed, clogged with hair, or obstructed by furniture, it will also prevent sufficient air from being drawn into the system. As with a clogged air filter, a lack of warm air flowing over the evaporator coil can lead to it freezing, and this is also something that you can easily check for and fix on your own with no issue. We would also recommend vacuuming your return air grilles once a month to prevent clogging. If you have pets, you may want to do this weekly since all of the air will cause the vent to clog more quickly.

3. Dirty Evaporator Coil

Dust and debris will always collect on the evaporator coil, which is one of the many reasons you should have your air conditioning system cleaned and maintained once a year. When too much dust builds up on the coil, it starts to insulate the coil and prevent the warm air from coming into contact with the coil. As with the other issues we’ve discussed, this can lead to the refrigerant remaining too cold and allow the water on the coil to start to freeze.

In this case, you will need to have a technician clean the coil, or your system will continually freeze. While coil-cleaning products are available in most home improvement stores, we would never recommend trying to clean your evaporator coil yourself. This is because you could easily damage the coil and create a refrigerant leak. Should this happen, you will usually need to have the coil replaced, which is far more expensive than hiring a technician to clean the coil for you.

4. Low Refrigerant Level

Your AC or heat pump system has to have a specific amount of refrigerant in order to work properly. Over time, the condenser coil, evaporator coil, and refrigerant lines can all begin to corrode to the point that refrigerant starts to leak out. If there isn’t enough refrigerant in the system, then the system will start to quickly freeze up every time you turn it on.

Unfortunately, this isn’t an issue you can detect on your own because you will need to have a technician check the refrigerant level. If the level is low, you will then need to have the entire system inspected as this indicates that there is a leak in one of the coils or refrigerant lines. Once the leak has been found and repaired, you will then need to have the refrigerant recharged so that your system then works properly again.

5. Broken Reversing Valve

A reversing valve is what allows heat pumps to both cool and heat because it enables the unit to switch the direction that the refrigerant flows. If you find that your outdoor heat pump unit freezes in the winter, it could be that the reversing valve is broken or stuck. Heat pumps need to occasionally defrost to prevent ice from forming on the outdoor coil. When defrosting, the unit reverses the refrigerant flow so that hot refrigerant flows through the unit. If the reversing valve is broken, the unit won’t be able to defrost and will start to freeze up.

If your HVAC is freezing up or having any other issues, you can count on the team at Nacogdoches Sheet Metal, Plumbing & Air Conditioning, LTD. for help. We service all makes and models of air conditioners and heat pumps, and our team can repair any HVAC problems. We also offer professional cooling maintenance and installation services, as well as a range of heating and plumbing services for customers throughout the Nacogdoches area. Give us a call today to schedule an AC inspection or any other HVAC service.