How the defrost cycle is terminated: coil sensor, time, and control logic

Defrosting should not continue longer than necessary. The controller uses specific criteria to decide when the outdoor heat exchanger has been cleared.

Coil temperature

When the outdoor heat exchanger temperature rises above a predetermined threshold, the system can determine that the ice has melted.

Maximum time

There is usually a safety time limit so that the defrost cycle does not remain active indefinitely.

Combined logic

Many systems use temperature, time, and other parameters simultaneously.

Termination problem

If the defrost cycle ends too early or too late, the sensor, sensor position, and controller logic should be checked.