What happens to an air source heat pump unit when the defrost cycle is activated?

When the defrost cycle is activated in an air source heat pump, the primary purpose is to remove frost buildup from the outdoor coil, which can hinder its performance. During this process, both the condenser fan stopping and the refrigerant flow reversing are critical actions that occur.

The condenser fan stops to allow the heat pump to effectively melt any ice on the outdoor coil without cooling air over it, which could counteract the defrosting process. Meanwhile, the refrigerant flow is reversed to allow the warm refrigerant to circulate through the outdoor coil, transferring heat to the coil and melting the frost. This combination is essential to ensure that the system can clear any ice accumulation efficiently.

By understanding these actions during the defrost cycle, one can appreciate the mechanisms in place that maintain the efficiency of the heat pump system, especially in cold weather conditions. The coordination of stopping the fan and reversing the refrigerant flow is crucial for the smooth operation of the system in maintaining heating performance.