Which component is responsible for energizing auxiliary heat during the defrost cycle?

The defrost relay plays a crucial role during the defrost cycle of a heat pump system. When the system identifies that frost has built up on the outdoor coil, the defrost relay is activated. Its primary function is to switch the system into defrost mode, allowing the heat pump to reverse its operation temporarily to melt the frost.

During this defrost cycle, the heat pump may require additional heat to ensure the indoor space remains comfortable. The defrost relay controls the activation of auxiliary heating elements, which provide that necessary heat. By energizing these auxiliary heat sources, the defrost relay ensures that the system can maintain the desired indoor temperature while the outdoor coil is being defrosted.

The other components listed do have their functions within the heat pump system. The compressor relay is primarily responsible for turning the compressor on and off, while the auxiliary heat switch controls the overall use of auxiliary heating when needed but is not specifically tied to the defrost process. The main thermostat is responsible for maintaining the set temperature in the living space but does not directly manage the defrost cycle or the activation of auxiliary heat during it.