K 2500 Truck 4WD V8-379 6.2L DSL VIN C FI (1989)
Blower Motor: Description and Operation
With A/C
CIRCUIT OPERATION: BLOWER CONTROLS
Battery voltage is applied at all times to Terminal 1 of the Low Blower Relay through RED (2) wire. When the Heater and A/C Controller is OFF, both
the Low Blower 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 951 and 963 of the Heater and A/C Controller are grounded, energizing the Low Blower and High Blower
Relay. Voltage is applied through the closed contacts of the Low Blower Relay, the YEL 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 applied to the Motor. With both Blower Resistors in the
circuit, the applied voltage is low and the Blower runs slowly.
In the Medium speed position, Terminal 963 of the Heater and A/C Controller is not grounded which de-energizes 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.
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/WHT (963) wire and the closed contacts of the High Blower Relay to the Blower
Motor. With battery voltage applied directly to the Motor, it runs at maximum speed.
