Hitachi Outdoor Coil Icing / Defrost Malfunction

Outdoor unit covered with ice in heating mode (heat pump models)

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Defrost control sensor fault, Outdoor coil very dirty, Low ambient temperature with high humidity, Faulty reversing valve or defrost logic

Safety first: Do not chip ice with tools; you may damage the coil.

Steps:

Allow defrost: Most Hitachi heat pumps automatically defrost. Observe if the unit periodically stops the outdoor fan and melts ice.
Clean coil: When ice has melted, clean the outdoor coil to improve defrost efficiency.
Clear drainage: Ensure melted ice can drain away and not refreeze around the base.

If the unit does not defrost or remains heavily iced: A technician should check defrost sensors, reversing valve, and control logic.

Hard 4/5

Outdoor Coil Thermistor / Defrost Control Circuit

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