Heating and Air Conditioning: Description and Operation

With the engine running, the GENERATOR applies Battery voltage through the normally closed contacts of the Restart Relay to the coil of the Heater and A/C Relay. Because the coil of the Heater and A/C Relay is permanently grounded at G102, the relay is immediately energized. With this relay energized, voltage is applied through Fusible Link FL-2 and Fuse E-1 to the BLOWER MOTOR. When the BLOWER SPEED SELECTOR SWITCH is moved to any position other than "OFF," the BLOWER MOTOR is provided with a ground through the BLOWER MOTOR RESISTOR and BLOWER SPEED SELECTOR SWITCH at G202.

With the BLOWER SPEED SELECTOR SWITCH in position "1," current must travel through the entire resistor element before reaching ground through the BLOWER SPEED SELECTOR SWITCH. As a result, the reduced voltage caused by the BLOWER MOTOR RESISTOR maintains the BLOWER MOTOR at speed "1."

With the BLOWER SPEED SELECTOR SWITCH in position "2," current travels only partially through the resistor element before reaching ground through the BLOWER SPEED SELECTOR SWITCH. Since less of the BLOWER MOTOR RESISTOR is part of the circuit, the resistance in the circuit is lower, the voltage is higher, and the BLOWER MOTOR operates at a higher speed than in position "1."


Operation in position "3," is identical to operation in position "2" with the exception that even less of the resistor element is used in the circuit. This causes the BLOWER MOTOR to operate faster in position "3" than in position "2," due to the increase in voltage.

When the BLOWER SPEED SELECTOR SWITCH is in position "4," current enters the BLOWER MOTOR RESISTOR but is not subjected to the resistor element. The BLOWER MOTOR operates on full Battery voltage.

The Restart Relay, when energized during cranking, stops heater operation by interrupting the circuit between the GENERATOR and the Heater and A/C Relay making heater system operation impossible during engine cranking.