K 2500 Truck 4WD V8-454 7.4L (1988)
Blower Motor: Description and Operation
With A/C
The AC clutch and blower motor are controlled by three relays that respond to output from the control panel relay driver. The driver will energize one or
more of the relays as needed to set the selected blower speed or engage the compressor clutch. Power to the relays is supplied through circuit 50 which
originates in the control head.
The control head controls the operation of the two blower relays to direct current through or bypass the blower resistors depending on the set blower
speed. The AC relay is also operated by the control head.
Circuit 50 supplies 12 volt switched ignition to the coil of each relay. The control head operates the circuit ground. By activating one or both of the two
relays, LO, MED, or HI, blower speed is achieved.
The blower speed is controlled by two resistors and two relays. When both relays are energized, current passes through the two resistors in series for
LOW speed. When the LOW blower relay is energized the second resistor is bypassed for MED speed. When the HI blower relay is energized, both
resistors are bypassed and the motor is connected directly for HI speed.
