Control Module HVAC: Description and Operation

Fan Control Module (Power Stage):
^ The Power Stage amplifies the control signals to operate the blower motor and control compressor operation.
^ The blower speed is controlled by a power transistor. A relay is connected into the circuit at the highest speed reduce the load on the transistor, while a second relay controls the operation of the compressor through the low-pressure pressostat on the air receiver/dryer.