Express 1/2 Ton Van V8-5.7L VIN R (1999)
Control Assembly: Description and Operation
Heating and Ventilation
General Information
The control assembly in the instrument panel contains a blower switch, a mode knob, and a temperature knob. The controls are back-lit when the
headlamps are ON. Electrical voltage passes through instrument panel lighting circuit. The instrument panel dimmer switch controls the dial illumination
brightness.
Blower Speed Control
The blower switch operates in the following 4 blower speeds:
^
LO
^
MED 1
^
MED 2
^
HIGH
The blower switch receives power from the heater and the a/c fuse when the ignition switch is in the ON position.
In the LO speed position, the circuit continues through the heater wiring harness to the 3 resistors in the blower motor resistor relay.
In the MED 1 speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but bypasses 1 of the 3 resistors.
In the MED 2 speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but bypasses 2 of the 3 resistors.
In the HIGH speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, but bypasses all 3 resistors and
closes the relay's normally open Contact to provide full power to the blower motor from the HVAC MaxiFuse.
From the blower resistor relay, the circuit moves to the blower motor terminal. The blower motor circuit completes to ground by a wire in the heater
wiring harness that moves from the blower motor terminal to the generator or the a/c compressor bracket.
Mode Control Knob
A vacuum from the mode knob controls the doors in the heater module, which controls the airflow through the heater module. The mode knob positions
are the following:
^
HTR
^
VENT
^
DEFROST
The intermediate positions are the following:
^
HTR
^
DEFROST
^
BLEND
When the mode knob is in the BLEND position, the controls are set to provide a combination of the features of the 2 nearest modes.
Temperature Control Knob
When the temperature knob is in the BLUE (cold) end of travel, the heater system delivers unheated air. When the temperature knob is in the RED (hot)
end of travel, all the air passing through the heater module is heated before being discharged. Intermediate positions of the temperature knob mix heated
and unheated air to provide more moderate air temperatures.
