When do the positions of the N.O. and N.C. switches change in a time initiation/temperature termination defrost?

In a time initiation/temperature termination defrost cycle, the positions of the normally open (N.O.) and normally closed (N.C.) switches change at specific intervals to maintain the efficiency of the heat pump system during defrosting. The choice of every 30 or 90 minutes reflects a common practice in such systems, allowing sufficient time for ice to build up on the evaporator coil yet also ensuring that it is removed at regular intervals to restore optimal performance.

This timing is critical because it balances the need for ice removal with energy efficiency. If the intervals are too short, the system may engage in unnecessary defrost cycles, wasting energy and straining components. Conversely, if the intervals are too long, frost can build up excessively, hindering heat transfer and leading to reduced performance. The 30 to 90-minute framework is designed to optimize the defrost cycle based on both time and temperature measurements, ensuring effective operation of the heat pump during winter conditions.