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What Does It Really Mean When Your AC Freezes And Why Does It Happen?

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You've probably heard of frozen air conditioners before and may have even experienced this condition yourself. Many people believe that air conditioning systems will freeze up when they run for too long, but this is only one potential source of the problem, and it often indicates another underlying issue. Understanding a little more about why this situation occurs can help you avoid some costly repairs.

Frozen Air Conditioners Defined

When your HVAC contractor tells you that your AC is freezing, they typically mean that your evaporator coil has ice on it. Although ice can form on other parts of your system, including your coolant lines, you won't usually notice until there's a solid coating on the evaporator. Once the problem reaches this point, you'll usually start noticing other symptoms with your air conditioner.

Your evaporator coil's job is to efficiently transfer heat from the air in your home to your air conditioning refrigerant. This process causes the coils to get cold, but AC designers carefully choose pressure levels that keep temperatures above freezing. This design ensures that water can condense onto the coils and drip away, helping to dehumidify the air in your home.

If temperatures drop too low, this condensed water will begin to form a layer of ice on the coils. The ice layer will reduce the coil's efficiency by acting as an insulator while preventing the AC from dehumidifying. As a result, you'll likely feel slightly colder, more humid air from your vents. Eventually, the compressor will overwork itself and shut down, stopping your system altogether.

How Air Conditioners Freeze

Although there are numerous potential reasons that an air conditioner might freeze, they all come down to two core problems:

  • Low refrigerant pressure
  • Restricted airflow

Refrigerant pressure and temperatures roughly correlate in an air conditioning system, which means lower pressure will lead to lower temperatures. Anything that causes a pressure drop will reduce the temperature at the evaporator coil, potentially leading to icing. The core problem may be a leak or even a restriction somewhere in the system.

Likewise, the evaporator needs warm air to help convert the refrigerant back into a vapor state. If there's insufficient airflow over the coils, the temperature will continue to drop, and the coils will ice over. Clogged filters, blocked vents, faulty blower motors, and even damaged evaporator coils can all potentially impact system airflow and cause your evaporator to freeze.

Whichever cause is true for your system, a frozen evaporator coil isn't a problem to ignore. Not only will it stop your system from working efficiently, but it can also damage your compressor. Never assume that your coils are freezing because your AC has been running for too long. Instead, call an AC repair professional to diagnose the issue so you can keep your home cool and avoid a more costly repair.