Can My HVAC System Freeze in the Winter?
By Melanie Dawn
November 15, 2024
If you own an HVAC unit, you’ve probably dealt with it freezing up in the summer at least once. But did you know your system can also freeze in the winter — even when it’s not extremely cold outside?
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Instead of warm air coming from the vents, it may blow cold air or not blow air at all. Outside, you may notice the unit is covered in a layer of frost or ice.
Reasons Your HVAC System Is Freezing Up
An HVAC system freezing up in the winter can be a major problem. For one, it won’t heat properly or as efficiently as it should. Eventually, it will also cause the compressor motor to burn out, and you’ll have to replace your outdoor unit. There are several reasons your heater or AC could be freezing up.
Clogged Air Filter
The most common reason your HVAC outside unit is freezing up is a clogged air filter. This should be the first thing you check for when you experience your AC unit freezing up or your heating unit freezing. As your system runs and air passes through the filter, it collects dust and debris. A dirty filter restricts airflow. This lack of airflow will cause the unit to freeze quickly. Open the filter panel and replace the filter. Check the return vents and replace filters in these areas if needed.
Dirty Evaporator Coils
Outdoor coils can accumulate dirt, grime and dust. When this happens, the unit can’t transfer heat. Lack of airflow will cause moisture on the coils to freeze and prevent normal operation. Turn off the HVAC unit and remove the panel on the inside unit. Check the manufacturer's manual if you're unsure where this is. Use compressed air or a soft brush to clean the coils. Replace the panel and turn the unit back on.
Faulty Defrost Cycle
Heat pumps have a built-in defrost mode that kicks in to remove frost and ice on the outside unit. If the defrost mode is malfunctioning, ice can build up and cause the unit to freeze. If you suspect a faulty defrost system or your HVAC unit is showing an error code, it's important to contact a professional for repairs.
Closed or Restricted Return Air Vents
If you’ve recently moved furniture around and have something sitting in front of a vent, airflow may be restricted. In some cases, vents may be blocked, or you may have closed them by accident. Check all the HVAC vents throughout your home. Open and clean the vents with a wet/dry vac to restore airflow.
Low Refrigerant Levels
An HVAC system must have a specific amount of refrigerant to work properly. Without enough fluid, your unit will freeze. Refrigerant issues should only be handled by an HVAC professional. If your coolant hasn't been checked in a while, it may be time for a maintenance call.
Broken Motor or Fan
Your fan motor and system blower work together to keep the air moving. If either of these components breaks down, airflow can be restricted, and the chance of your HVAC unit freezing up increases. If you notice a lack of airflow or strange noises coming from your vents, you should contact an HVAC technician to diagnose and address any motor or fan issues.
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How to Prevent Your HVAC System From Freezing Up
Regular maintenance is a key factor in preventing HVAC freeze-up, as it keeps your system running as it should year-round. Some maintenance steps you can take on your own include:
Replace Your Filter
Check your air filter at least once a month and replace it at least once every three months. Frequency will depend on how dusty your home is, whether you have pets and what type of filter you have. Typically, thicker filters need to be changed less often, while high-efficiency filters should be replaced more frequently.
Clean the Fan
Locate the blower motor, which is usually in the base of the unit near the air filter. Use a wet/dry vac to remove any dust or debris and clear away any trash or objects blocking the fan.
Check Your Vents
Inspect each vent and make sure it's open and clean. One or two blocked vents can reduce airflow and increase energy costs.
Clean the Outdoor Coils
It’s common for vines and other vegetation to grow in and around your outdoor unit. Clear away leaves, insects and other debris that can restrict airflow.
Contact a Professional
If you’ve performed a routine check and your system is still freezing up, contact an HVAC professional. They'll calibrate your thermostat and properly diagnose any problems you may be experiencing.
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