Why Is My Outside AC Unit Frozen? A Tech from Southern California Explains

By Your Advisor 4/22/21 12:17 PM Time to read:

If your outside AC unit is frozen, this isn’t normal.

Here’s a very simplified explanation for what’s happening: Your AC is freezing up because something in the system is causing your refrigerant temperatures to drop. This can cause the evaporator coil (part of the inside unit) and/or the condenser coil (part of the outside unit) to freeze up.

A few different AC problems can cause your refrigerant temperatures to drop and freeze up the system, including:

  • A clogged air filter
  • A dirty evaporator coil
  • Obstructed air vents
  • A refrigerant leak

To help you troubleshoot, we’ll explain each of the issues above and show you what you can do to try and fix the problem before calling a professional.



If you’ve exhausted the tips below, you’ll need a professional to inspect, diagnose and repair your AC. If you live in or around the Redlands/Inland Empire area, just contact us and we’ll send a licensed technician over as soon as possible.

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Problem #1: A clogged air filter

Why this causes the AC to freeze up:

If your air filter is clogged, it restricts air from passing over your evaporator coil (part of the inside unit). If warm, unconditioned air doesn’t pass over the coil, the temperature of the refrigerant inside the system drops and can freeze over.

clean-dirty filters - crop

What to do:

Start by replacing the clogged air filter with a new one. Then, turn off your system and allow it time to thaw out. Once it is thawed, run the system as usual. If there are additional problems, contact a professional to evaluate your AC system. 

Burgeson’s can help. Simply contact us online or via phone and we’ll send a technician to your home as soon as possible.

Problem #2: A dirty evaporator coil

 

Why this causes the AC to freeze up:

Over time, dirt, dust and other contaminants from your home’s air can cling to your AC system’s evaporator coil (inside unit). Even a thin layer of dirt on the coil can cause it to freeze over.

That layer of dirt can act as a barrier between the cold coil and warm unconditioned air from your home. If the evaporator coil doesn’t get enough contact with warm air, the temperature of the refrigerant inside the coil will continue to drop until it freezes over.

hvac-air-conditioner-evaporator-coil-dirt-and-air-flow-4

What to do:

Have a professional clean your indoor coil. This repair shouldn’t be attempted by a homeowner as your evaporator coil is located inside your air handler and contains refrigerant, a gas that can be harmful to humans.

Problem #3: Obstructed air vents

Why this causes the AC to freeze up:

Your AC system cools by pulling in warm air from your home and stripping it of heat. If there isn’t enough warm air being sucked in through your return air vents and blown over the evaporator coil (the equipment that strips away the heat), then the evaporator coil could freeze. 

If furniture, curtains, or other objects are obstructing the air vents in your home (see below), this prevents air from being passed through the system. Restricted airflow can cause the coil to ice over.

blocked air vent

What to do:

Check to make sure that all of your vents are unobstructed and have plenty of space for the air to circulate in your home.

Problem #4: Low refrigerant levels

Why this causes the AC to freeze up:

Refrigerant is the substance in your AC system that absorbs heat from your home’s air. If refrigerant levels are low, the system can’t absorb as much heat as it’s supposed to. Over time, the refrigerant will drop in temperature, which will eventually cause your AC’s coil to freeze over.

What to do:

Hire a professional HVAC contractor immediately. The refrigerant in your AC system doesn’t get “used up” like gas in a car. That means that if levels are low, there is a refrigerant leak somewhere in the system. A professional will need to inspect the system to find the leak, fix it, then recharge the system.

Need help getting your AC back to a healthy operation? Choose the Pros at Burgeson’s!

Burgesons’ has been serving the Redlands and Inland Empire area for over 72 years. That said, we take our relationships with our customers seriously. When you choose us, you’re not just getting a highly qualified and skilled technician, you’re also getting a polite professional who has been trained to put your comfort first. 

If you need help getting your frozen AC back to a healthy operation, Burgeson’s is here to help!