Express 1/2 Ton Van V6-4.3L VIN W (1999)
Housing Assembly HVAC: Description and Operation
Heating and Ventilation
Auxiliary Heater
An optional auxiliary heater supplies heat to the vehicle. The unit operates independently of the standard heater. The control on the instrument panel
regulates the unit. The system consists of a separate heater core and the blower fan.
The heater hoses extend from the unit to a vacuum operated water valve. The hoses connect to the standard heater hoses.
A 3 position vacuum operated water valve cuts off the coolant flow in the OFF position. The water valve eliminates radiant heat, and reduces the coolant
flow in the LO and MED positions.
Blower Speed Control-Auxiliary
The 3-speed blower switch provides the following settings:
^
LO
^
MED
^
HIGH
The blower switch is located in the instrument panel, above the radio. The blower switch also triggers an electro-mechanical valve to control coolant
flow to the auxiliary heater core.
In the LO speed position, the circuit continues through the heater wiring harness to 2 resistors in the blower motor resistor relay.
In the MED speed position, the circuit continues through the heater wiring harness to 1 resistor in the blower motor resistor relay.
In the HIGH speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, and closes the relay's normally
open contact. This provides full power to the blower motor from the HVAC MaxiFuse(R).
General Information
Within the heater module is a series of valves called the temperature valve, the vent valve and the defroster valve. Valves are hinged components that
direct airflow through the various sections of the heater module. The valves provide the proper airflow for the selected operating mode.
Heater System Description
The heater system provides heating, ram air, power ventilation, and the windshield defrosting. The blower fan draws outside air from the plenum at the
base of the windshield into the heater module. The forward movement of the vehicle forces additional outside air, or ram air, into the heater module.
Within the heater module, the air is heated. The heated air is routed through the ducts to the proper outlets for discharge into the passenger compartment.
A control assembly in the instrument panel allows the operator to control the blower speed, the mode of operation, and the temperature of the air coming
from the heater system.
The heater module contains components that heat the air, and direct the air to the proper ducts and outlets. The components are enclosed inside a two
part housing. The front housing mounts to the front of the cowl panel in the engine compartment. The rear housing mounts to the rear of the cowl panel
in the passenger compartment under the instrument panel.
Blend Mode
When the mode knob moves to the BLEND position, the defroster valve moves to uncover more of the opening to the defroster. An increasing amount of
air flows to the defroster nozzle, and a decreasing amount of air flows to the heater duct.
Defrost Mode
When the mode knob is in the DEFROST position, the defroster valve moves to fully uncover the opening to the defroster nozzle and restrict the opening
to the heater duct. The defroster nozzle receives the maximum airflow, with only a little amount of airflow coming from the heater duct.
General Information
The heater system provides the following 3 basic operating modes:
^
VENT
^
HTR
^
DEFROST
The system also can combine the features of HTR, and DEFROST into 1 position called BLEND.
Heater Mode
When the mode knob is in the HTR position, the vent valve partially closes. The defroster valve remains closed. The blower fan heats the air and directs
the heated air to the defroster valve. The defroster valve sends most of the airflow to the heater duct and some to the defroster nozzle.
Vent Mode
With the mode knob in the VENT position, the vent valve opens so air can flow to the instrument panel outlet ducts.
Temperature Valve and Heater Core
The temperature of the air coming from the heater duct and the defroster nozzle is regulated by controlling the relative amounts of warm and cool air
coming from the heater module. The temperature valve determines the amount of the total airflow that passes through the heater core.
