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

If your outside AC unit is frozen, that's not 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 too low. This can cause the evaporator coil (part of the inside unit) and/or the condenser coil (part of the outside unit) to freeze. This often leads to your air conditioner icing up.

To help you troubleshoot, we’ll explain the common causes of your AC unit freezing and show you what you can do before calling a professional. If you're asking, "Why is my AC frozen?", this guide will help.

• A Clogged Air Filter
• A Dirty Evaporator Coil
• Obstructed Air Vents
• A Refrigerant Leak
• Thermostat or System Issues
• Mechanical Failures
• Poor Maintenance

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.

A Clogged Air Filter

A clogged air filter restricts air from passing over your evaporator coil (part of the inside unit). When warm, unconditioned air can’t pass over the coil, the temperature of the refrigerant drops too much, causing the coil to freeze eventually. This is one of the most common reasons homeowners ask, “Why is my AC frozen?”

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 completely. Once it is thawed, run the system as usual. If there are additional problems, contact a professional.

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

A Dirty Evaporator Coil

Dust and debris can accumulate on your evaporator coil over time. Even a thin layer of dirt can prevent the coil from effectively transferring heat, leading to temperatures that cause the air conditioner to freeze up.

WHAT TO DO:

Contact an HVAC professional to clean your indoor coil. Because this component contains refrigerant and is located inside the air handler, it should only be serviced by a licensed technician.

OBSTRUCTED AIR VENTS

Blocked or closed vents prevent warm air from properly circulating through your AC system. With limited airflow, the evaporator coil can’t absorb enough heat—causing it to get too cold and possibly freeze.

What to do:

Ensure that all supply and return vents in your home are open and unobstructed by furniture, rugs, or curtains. Proper airflow is essential to prevent your air conditioner from icing up.

A Refrigerant Leak

Low refrigerant levels reduce your AC coil’s ability to absorb heat. When this happens, the temperature of the refrigerant drops too much and can cause the evaporator coil to freeze eventually.

What to do:

Call a licensed HVAC technician immediately. Refrigerant does not deplete naturally—it escapes due to a leak. A technician will need to locate and repair the leak before recharging the system.

Thermostat or System Issues

Incorrect thermostat settings or a faulty thermostat can cause your system to run when outdoor temperatures are too low. This can lead to coil temperatures dropping below safe levels, which can result in your air conditioner icing up unexpectedly.

What to do:

Make sure your thermostat isn’t set too low, especially in cooler weather. If your system continues to freeze up or short cycle, have a technician check for wiring or sensor issues.

Mechanical Failures

A malfunctioning blower fan or broken expansion valve can disrupt airflow or refrigerant flow. If the blower fan isn’t working properly, warm air won’t reach the evaporator coil, and the coil can freeze. A faulty expansion valve can allow improper refrigerant flow, possibly resulting in your air conditioner icing up.

What to do:

Have your system inspected by an HVAC professional. These components require diagnosis and repair from a trained technician to restore proper function and prevent future freezing.

Poor Maintenance

Lack of routine AC tune-ups and overdue filter changes or coil cleaning can lead to a variety of problems, including frozen coils. Regular maintenance helps prevent issues and keeps your HVAC system running efficiently.

What to do:

Schedule routine maintenance with a licensed technician. Regular inspections, cleanings, and filter replacements can prevent many common causes of freezing and extend the life of your AC system.

Final Thoughts

A frozen outside AC unit is a sign that something is wrong—whether it’s restricted airflow, a refrigerant issue, or a mechanical problem. If you're wondering, “Why is my AC frozen?”, start by checking for simple problems like a dirty filter or blocked vent.
Still seeing ice? Don’t risk further damage—contact the professionals at Burgeson’s.

Need Expert Help?

Burgeson’s has been serving the Inland Empire and beyond for over 76 years, and we take. That said, we take our relationships with our customers seriously. When you choose our team, 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. Our certified technicians are trained to diagnose and repair issues like air conditioners icing up with fast, courteous service.

Schedule an appointment online today or call us at (909) 792-2222—we’ll help you get your AC back to healthy, ice-free operation.