K 3500 Truck 4WD V8-454 7.4L VIN J SFI (1996)
Control Assembly: Description and Operation
Blower Controls
Battery Voltage is supplied at all times to Front High Blower Relay Pin A2 through the RED (542) wire. When the ignition Switch is OFF or the Front
Blower Switch at the Heater Control Module or Heater and A/C Control Module is OFF, no Voltage is applied to the Relay Coil through the ORN (52)
wire and the Relay remains de-energized. Similarly, no Voltage is applied to the normally closed contact at Pin B2 of the Relay. Battery Voltage is not
applied to the Front Blower Motor and it does not operate at any speed.
When the Ignition Switch is in RUN and the Front Blower Switch is in LO, Voltage is applied through all three Blower Resistors to the normally closed
contact in the Relay. The Relay remains de-energized. Reduced Voltage is applied to the Front Blower Motor through the PPL (65) wire and the Motor
operates at its slowest speed. With the Front Blower Switch in either M1 or M2, current flows through fewer resistors in the Front Blower Resistor and
the Front Blower Motor runs faster.
With the Front Blower Switch in HI, the Blower Resistors are bypassed by the energizing of the Front High Blower Relay. The contacts change state and
Battery Voltage from the Underhood Fuse-Relay Center is applied directly to the Motor. The Front Blower Motor then operates at it's fastest speed.
