1992 Volvo 740 L4-2320cc 23L DOHC B234F HVAC Control Module Diagrams
Control Module HVAC: Description and Operation
Fan Control Module (Power Stage):
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The Power Stage amplifies the control signals to operate the blower motor and control compressor operation.
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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.