How to Fix a Frozen Evaporator Coil

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Air conditioning systems contain two separate coils, an evaporative coil and a condenser coil. The condenser coil sits outside the home, removes the heat gathered from indoors and releases the collected heat to the outdoors. The evaporative coil is placed inside the air conditioning ductwork of the home. It is this coil that gets cold and pulls unwanted heat from the enclosed area. One of the most common reasons for an evaporative coil to freeze over is a dirty air filter or debris on the coil itself.

Things You'll Need

  • Vacuum cleaner
  • Brush attachment for vacuum cleaner
  • New air filter

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Shut off the air conditioning system. Remove all electrical power from the unit by turning off the circuit breakers or pulling the fuses that supply power to the air conditioning unit.

Open the intake air grill and remove the old air filter. Use the vacuum cleaner and remove any accumulated debris found inside the ductwork. (This debris can collect on the evaporative coil and reduce the airflow through the coil’s fins, causing the coil to freeze over.)

Gain access to the evaporative coil. Location varies according to the manufacturer. Consult the specifications for your unit to find access to the coil. If the coil is frozen solid, allow it to thaw completely before using the system.

Clean the aluminum fins on the evaporative coil by vacuuming the fins. Place the brush attachment on the end of the vacuum hose. Move the brush in the same direction as the fins on the coil. Remove as much of the accumulated debris as you can.

Place a new air filter in the intake air grill. Change the air filter at least every month when the unit is operating.

Tips & Warnings

  • Contact a licensed HVAC technician if you are unable to remedy the problem. If the steps above do not aid in the solution, the problem may be internal to the air conditioning system.
  • The evaporative coil can also freeze over if the unit is operated when outdoor temperatures are below 65 degrees F, or if the indoor temperature drops below 72 degrees F. If too many outlet ducts are closed, this will restrict the airflow through the coils and cause a freezing condition.


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