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Why Are My AC Coils Frozen?

Posted on: September 21, 2022

Close-up view on AC unit fan blades spinning.

Frozen air conditioner coils will do anything but help you chill out. When your evaporator coils freeze up, it’s a sign that your air conditioner isn’t functioning correctly and requires your attention.

Depending on the cause of the problem, you may need to schedule an air conditioner service so a qualified HVAC technician can accurately diagnose the problem.

If you have frozen evaporator coils, these are some of the possible reasons and what you can do about it.

Insufficient Airflow

This is the leading cause of frozen AC coils. It can happen because you have dirty air filters, debris around your coils, or problems with your air ducts, such as leaks or obstructions. This reduces your system’s ability to keep the AC coils warm and prevent them from freezing.

Refrigerant Leaks

Another common cause of frozen AC coils is refrigerant leaks. As the leak progresses, it reduces the pressure within the coils and the ability of the AC coil to absorb the heat. This causes the coil to absorb more heat than it’s designed to, resulting in the coils freezing over.

Blocked Condensate Lines

These lines drain excess moisture from the humid air before depositing it via pipes to your floor drain. When this path gets blocked, it can freeze, and if it occurs near the AC coils, it can cause them to freeze over.

Broken Fans

A broken fan means air isn’t being adequately pushed through your air conditioner system. If you have a broken fan or a malfunctioning blower motor, this will reduce airflow and cause your AC coils to freeze.


It’s rare for the temperature to drop below freezing here, but it can happen. If there’s a sudden temperature change, it can cause your AC coils to freeze.

Preventing Frozen AC Coils

Preventing frozen AC coils is always better than trying to repair them. This is why we strongly recommend homeowners perform regular checkups of their system to confirm everything is working properly.

To that end, here are some simple steps you can take to protect yourself from the inconvenience of frozen AC coils:

  1. Regularly inspect your air conditioner for leaks. If you notice pooling water or visible refrigerant, schedule an AC service immediately.
  2. Clear away debris. Ensure all vents and areas around your air conditioner are clear of leaves, branches, trash, and other debris.
  3. Check your ductwork. Visually inspect your ductwork and registers. Make sure they’re not blocked and that the ducts are properly secured and sealed.
  4. Listen to your AC. How does the motor sound? How about the fan blades? Schedule a service with a certified HVAC technician if you hear rattling, banging, grinding, screeching, or notice your system is short-cycling.
  5. Maintain your air conditioner. A certified HVAC technician should perform AC maintenance every spring, and an inspection should be scheduled again in the fall. Staying on top of maintenance will stop your AC from freezing and help preserve any warranty coverage.

Have more questions about frozen evaporator coils? Contact SM Air at (512) 212-4777 to speak with our certified, licensed, and insured HVAC technicians.

We’re always ready to answer your questions and help you find the best ways to keep your air conditioner ready on the hottest days of the year in San Marcos, TX.