Why is my AC unit freezing up?

HVAC technician determining why an AC unit is freezing up

October 26, 2022

If your air conditioning unit freezes up on a hot summer day, you know you’re in trouble. It’s about to get dangerously uncomfortable in your home. But what causes AC units to freeze up?

Unfortunately, AC units freezing over is one of the most common ways your unit can fail. Some people might see ice forming on their units and think “Oh, it’s working really well!” But in reality, it’s the tell-tale sign of impending disaster.

Let’s discuss what makes your AC unit freeze over and how you can avoid it in the future.

Clogged Air Filters & Ducts

If your AC unit’s air filter is dirty, your unit will suffer from insufficient airflow. The same applies to clogged ductwork.

Even if the other mechanical components of your HVAC system are working fine, air not passing properly through the evaporator coil leads to a layer of ice developing.

Manufacturers recommend changing the air filter every few months. Some recommend changing it each month, especially if your home is particularly high-activity. Be mindful of dusty indoor environments!

HVAC Mechanical Issues

Your AC unit can freeze over and suffer from decreased performance if your blower fan stops working properly. Blower fans are what many HVAC technicians check first when a system is going through mechanical issues.

Since the blower fan can’t send warm air through the system, the cold builds up and creates a layer of ice that simply won’t melt over time. At critical mass, that ice can cause your system to shut down altogether.

Keeping your blower fan working properly is tied to routine preventative maintenance. Make sure you schedule such services with your HVAC company to avoid a frozen AC unit!

Check Your Thermostat Settings

You might think keeping your AC fan set to “low” means you’ll use less energy. But in reality, that means it has to do twice the work, which can strain your entire AC system.

Air circulation is critical for keeping appropriate refrigerant levels in the system. If that cold refrigerant moves too slowly, it can cause ice to form on your evaporator coils.

Additionally, you shouldn’t run your air conditioning on cool when temperatures outside are particularly low. This can cause the internal temperatures in the machine to go way lower and the system will freeze over.

Additional Issues

Other causes of AC units freezing over include:

  • Clogged condensate drain lines
  • Low refrigerant levels
  • Dirty evaporator coils
  • Faulty compressor
  • Damaged condenser fins

If your AC unit keeps freezing up and you aren’t sure of the cause – or if you need an immediate fix, contact the professionals. At Charlie’s Tropic Heating & Air, we know exactly how to solve your issue and keep it from happening in the future. Contact us today to schedule HVAC services for your home!

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