A frozen air conditioner is both inconvenient and potentially costly. It prevents you from cooling your home and, unless it’s addressed quickly, could burn out your compressor, the most expensive component of your AC system. There are five reasons your AC unit is freezing up. Some can be fixed on your own, while others require professional help.

Poor Airflow

Every air conditioner has two sets of coils that work in tandem. The evaporator coils absorb heat; the condenser coils dispel it. Each one requires steady airflow to manage its respective task. Unless air is moving constantly through the system, the condenser coils will overheat and the evaporator coils will freeze up.

Poor airflow is normally the result of a clogged dust filter. Filters trap dirt, debris, and pollen before they can be blown out into your home. However, over time, they can become so dirty no air can get through. Without warm air to moderate their temperature, the evaporator coils will become so cold they freeze.

However, if the filter’s fine, then your vents may be the problem. Furniture or heavy curtains can block circulation, forcing cold air back through your ducts and into the air conditioner.

Dirty Coils

When dirt builds up on your evaporator coils, it acts like an insulator, preventing them from absorbing heat. As a result, the temperature inside the coils starts to drop until eventually, they start to freeze. This creates a feedback loop. The ice on the coils reduces heat absorption, which leads to more freezing.

Dirt also hinders airflow. Filters are supposed to catch dirt before it reaches your coils, but even the best filters won’t catch all of it. Eventually, enough can accumulate to stop air from flowing over your evaporator coils, at which point they’ll likely freeze up.

Blocked Condensate Line

Whenever warm air comes into contact with a cold surface, it cools the air until it eventually reaches its dew point and forms condensation. This same process occurs inside your cooling system as warm air comes into contact with your evaporator coils. Normally, this excess moisture is collected and drained by the drip pan and condensate line. However, if the line is blocked, moisture will build up inside the unit and eventually freeze, if the coils are cold enough.

Broken Fan

Fans circulate air through your system and your home. When they break down, the cold side of your air conditioner stops absorbing heat. Without a way to balance the temperature, ice starts to accumulate inside.

Low Refrigerant

Refrigerant is a chemical that circulates through your cooling system, absorbing heat inside your home and transferring it outside. The temperature of your refrigerant depends on its pressure. When the pressure is too high, the system overheats. When it’s too low, the temperature drops and freezes the moisture inside the unit.

Air conditioners are closed systems. All the refrigerant is supposed to stay safely sealed inside. If the pressure drops, the unit was either charged incorrectly or one of the refrigerant lines has sprung a leak. Regardless, you’ll need to call an HVAC technician to fix the leak and refill the system.

What to Do When Your AC Unit Freezes Up

A frozen AC unit generally isn’t hard to detect. The first sign is your air conditioner isn’t cooling your house properly. There will also be ice around the outdoor refrigerant line and moisture on the condensate drain. You can also remove the panel on your air conditioner with a screwdriver and check inside.

Once you know your AC unit is freezing up, shut it off, and let it defrost. Running the fan will speed up the process, as long as the cooling system is disengaged. After the ice is gone, check your air filter. If it’s dirty, replace it with a clean one. Also, examine your indoor vents to make sure they’re unobstructed.

When that’s done, reactivate your cooling system and monitor its performance. If it starts cooling again like normal, then the unit was suffering from poor airflow and nothing else needs to be done. However, if you see ice forming again, shut it down, and call an HVAC contractor to diagnose the problem.

Protect Your Cooling System

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