Defrost cycle in a heat pump: exactly what happens step-by-step

Defrost is the process by which the heat pump removes ice from the outdoor exchanger.

Initiation

The controller decides that a defrost is needed using temperatures, operating time, and other parameters.

Cycle reversal

The four-way valve temporarily reverses the refrigeration cycle so that the outdoor exchanger heats up.

Ice melting

Thermal energy is directed to the outdoor exchanger and the ice melts.

Termination

When the sensor indicates that the exchanger is clear or the specified limit is reached, the system returns to heating.

What the user sees

For a few minutes, heating may be reduced and water vapor may appear around the outdoor unit.