What Causes Ice on my Air Conditioner?

Air conditioners need regular attention to maintain a comfortable home during the heat of the summer. However, on rare occasions, an AC will freeze up, and it helps to know what causes this problem so that you can avoid it. The cause can be as simple as missed maintenance, or result from a serious problem within the unit. If you suspect issues with ice or any other serious mechanical problems for the AC in your Mount Pleasant, Texas, home it’s best to promptly contact a professional for service.

Mechanical Problems

A faulty thermostat can cause the AC to cycle too slowly, causing ice build-up. A malfunctioning or maladjusted thermal expansion valve may allow refrigerant to expand too quickly. Low refrigerant is a common cause of an AC freezing up. It’s low either because there’s a leak or because not enough refrigerant was used in the first place.


In humid weather, an air conditioner can produce a quart and half of water every hour from condensation in the evaporator. Don’t be alarmed if you occasionally see a lot of water drainage. However, if it doesn’t drain fast enough, ice can form under coils and obstruct the drain. Check the drain pan for wear, obstructions, and rust. Your technician can clear out the drain line regularly by flushing it with a high-pressure hose. A shop vacuum can be used to remove any clogs.


An AC that is starved for air can’t evaporate moisture on the coils fast enough to prevent ice. To help keep the airflow going:

  • Follow the manufacturer’s recommendations for the air filter. Always change it on time and check it in between changes. What causes air conditioners to ice up is often a dirty filter.

  • You don’t save cooling costs by closing registers. Leave registers open for best airflow. Avoid placing furniture or any other large object over the registers.

  • Have your ducts checked as holes, gaps or damage to ductwork can impact airflow.

What to do when the AC Freezes

Turn off the AC at the thermostat immediately and allow it to thaw. Running a frozen AC may damage or destroy the compressor. Contact your HVAC technician who will make the necessary checks, tests, and repairs to get your AC functioning again.

Contact Wood Air Conditioning & Plumbing today at 903-285-6550 for expert help and to prevent ice buildup on your air conditioner.

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