K 3500 Truck 4WD V8-454 7.4L (1994)
Blower Motor: Description and Operation
With A/C
CIRCUIT OPERATION
Battery voltage is supplied at all times to Terminal 1 of the Low Blower Relay through RED (2) wire. When the Heater and A/C Controller is
OFF, the Low, Medium and High Blower Relays are de-energized. In this state there is no voltage path through the relay contacts to the Blower
Motor so the Blower Motor does not run.
With the Blower Mode in Low, Terminals 1649 and 1650 of the Heater and A/C Controller are grounded, energizing the Low Blower and High
Blower Relay. Voltage is supplied through the closed contacts of the Low Blower Relay, the YEL (51) wire and the two Blower Resistors to the
Blower Motor. The Blower Motor is a variable speed motor which runs at a speed proportional to the voltage supplied to the Motor. With both
Blower Resistors in the circuit, the supplied voltage is low and the Blower runs slowly.
In the Medium speed position, Terminal 1650 of the Heater and A/C Controller is not grounded which deenergizes the High Blower Relay. In the
de-energized state, the contacts of the Relay shunt one of the Blower Resistors allowing the Blower Motor to operate at increased speed.
Blower Relay Positions
With the Blower Mode in High, the Low Blower Relay is de-energized and the High Blower Relay is energized. The voltage path is then through
the normally closed contacts of the Low Blower Relay, the DK GRN (249) wire and the closed contacts of the High Blower Relay to the Blower
Motor. With battery voltage supplied directly to the Motor, it runs at maximum speed.
