C 1500 Truck 2WD V8-5.3L VIN T (1999)
Control Assembly: Description and Operation
HVAC System - Manual
HVAC Blower Controls Circuit Description
Battery voltage is supplied to the blower motor resistor relay assembly connector C1 cavity G via CKT 540 (ORN) at all times. When the ignition switch
is OFF or the blower switch is in any position except HI, no voltage is applied to the relay coil via CKT 52 (ORN) and the relay remains de-energized.
With the blower switch in HI, the blower resistors are bypassed and voltage is supplied to the coil side of the permanently grounded relay. This closes
the contacts and supplies full battery voltage from the Underhood Bussed Electrical Center (UBEC) to the blower motor which will operate at the
highest speed.
When the blower switch is in LO to any medium speed, voltage is reduced through the appropriate resistors which will limit the blower speed
accordingly.
The blower motor resistor relay assembly is located next to the blower motor under the right side of the glove compartment.
Blower Motor Speed Control
The blower switch provides a choice of various blower speeds. A fuse in the fuse block provides power to the blower switch when the ignition is turned
to the ON position. In the low speed position, the circuit continues through the heater wiring harness to the 4 resistors in the resistor assembly. The
resistor assembly is near the blower motor.
When the blower switch is in the medium speed position, the circuit continues through the heater wiring harness to the resistor assembly. This circuit
then bypasses 1 or 2 of the resistors.
When the blower switch is in the HI position, the circuit continues through the heater wiring harness to the resistor assembly. The circuit bypasses all 3
resistors in order to provide full power to the blower motor.
Controls
