When the contacts of the room thermostat close making terminals R to Y & G, the low voltage circuit of the transformer is completed. Current now flows through the magnetic holding coils of the compressor contactor (CC) and fan relay (RFC).
This draws in the normally open contact CC, starting the compressor and condenser fan motors. At the same time contacts RFC close starting the indoor fan motor. When the thermostat is satisfied, it opens its contacts, breaking the low voltage circuit, causing the compressor contactor and indoor fan relay to open, shutting down the system.
If the room thermostat fan selector switch should be set on the “on” position, then the indoor blower would run continuous rather than cycling with the compressor.
Heat pumps energize the reversing valve thorough the “O” circuit in the room thermostat. Therefore the reversing valve remains energized as long as the thermostat subbase is in the cooling position. The only exception to this is during defrost.
