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Cooling Troubleshooting

Frozen Evaporator Coil

Learn why an air-conditioner evaporator coil can freeze, what low airflow and refrigerant conditions can do, and why the system should not be operated while the coil is iced.

What It Can Mean

Start with the symptom, then narrow the cause

Ice on the evaporator coil or suction line means the indoor coil has been operating below freezing while moisture is present. Once ice forms, airflow becomes even more restricted and cooling performance deteriorates quickly.

Low airflow is one common cause, but refrigerant conditions, metering issues and other system faults can also produce abnormally low evaporator temperatures.

Do not continue running the compressor with a frozen coil. The coil needs to thaw and the underlying cause needs to be corrected.

Possible Causes

Common conditions associated with this symptom

Dirty filter

A heavily loaded filter can reduce airflow across the indoor coil.

Blower or airflow problem

A failed blower, incorrect speed, dirty coil or duct restriction can reduce heat transfer into the refrigerant.

Refrigerant undercharge

Low refrigerant mass flow can contribute to low evaporator pressure and temperature.

Metering problem

A restriction or control issue at the metering device can alter refrigerant feeding.

Closed or restricted duct system

Excessive static pressure can reduce total airflow even when the blower is operating.

Low indoor load

Unusual operating conditions combined with other issues can contribute to excessively low coil temperature.

Important

Do not diagnose by symptom alone

Several different HVAC faults can produce the same homeowner symptom. Proper diagnosis may require electrical readings, refrigerant measurements, airflow testing, static-pressure measurements, combustion testing or control-sequence checks.

Do not bypass safeties, open sealed refrigerant circuits, work on gas piping or perform live electrical troubleshooting unless you are qualified to do so.

Call for Service

Professional evaluation is appropriate when

  • The coil freezes again after thawing.
  • The blower is not moving air.
  • You suspect a refrigerant leak or metering problem.
  • Water from thawing ice is overflowing or reaching electrical components.
  • The system has a history of repeated freeze-ups.
Need More Help Narrowing It Down?

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Related Troubleshooting

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When requesting service, include the equipment type, approximate age, when the problem started, whether the system still operates and any unusual noise, water, odor or thermostat behavior you have noticed.

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