Express 3/4 Ton Van V8-6.5L DSL Turbo VIN F (1999)
position grounds the coil of the auxiliary blower motor low speed relay through the wire for CKT 1926 (DK BLU) and CKT 60 (YEL). Placing the rear
auxiliary HVAC control module in the MED position grounds the coil of the auxiliary blower motor medium speed relay through the wire for CKT 1925
(RED) and CKT 63 (TAN).
Placing the rear auxiliary HVAC control module in the HI position grounds the coil of the auxiliary blower motor high speed relay through the wire for
CKT 1924 (WHT) and CKT 52 (ORN).
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 three resistors in the resistor assembly, near the
blower motor.
When the blower switch is placed in the medium speed position, the circuit continues through the heater wiring harness to the resistor assembly. This
circuit then bypasses one or two 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 then bypasses
all three resistors in order to provide full power to the blower motor.
From the resistor assembly, the circuit goes to the blower motor terminal in order to operate the blower motor.
Controls
The heater control head in the instrument panel contains the following controls:
^
A blower speed control knob
^
A desired operation selection knob
^
An air temperature control knob
These controls are illuminated when the headlamps are ON. The instrument panel lighting circuit provides the voltage. The dimmer control of the
headlamp switch controls the brightness of the dial illumination.
Mode Control Knob
The mode knob operates a rotary vacuum that routes engine vacuum to specific hoses in the vacuum harness. These hoses control vacuum actuators on
the HVAC module. Each actuator operates a valve, a door-like hinge deflector, that routes airflow to the various outlets of the heater system.
The mode knob has the following positions:
^
MAX A/C
^
NORM A/C
^
BI-LEV A/C
^
VENT
^
HTR
^
BLEND
^
DEFROST
Temperature Control
When the temperature knob is in the COLD (blue) position, the air delivered by the HVAC system is unheated. When the temperature knob in the HOT
(red) position, all of the air that passes through the heater module is heated before the air is discharged. Intermediate positions of the temperature knob
result in a mixture of heated and unheated air in order to provide more moderate air temperatures.
When you move the temperature knob away from the cold position, the temperature valve moves away from the heater core in order to allow for some air
flow through the heater core. The more you move the temperature knob toward the hot position, the greater the air flow through the heater core. Heating
a greater portion of the airflow in this manner results in a warmer discharge of air from the outlets.
When the temperature knob is in the full hot position, the temperature valve blocks off the passage that allows air to bypass the heater core. This causes
all of the airflow to go through the heater core for maximum heating. This method of temperature control provides a very rapid response to any change in
temperature selection throughout the entire range when the engine is warmed up.
An electric motor, not a cable system, controls the temperature door.
