Express 1/2 Ton Van V6-4.3L VIN W (1999)
Housing Assembly HVAC: Description and Operation
HVAC System - Manual
Ducts and Outlets
A system of ducts and outlets directs air to the passenger compartment. In case of poor air output, inspect for obstructions in the following vent ducts:
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The defroster
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The heater
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The air conditioning
General Information
NOTE: R-12 refrigerant and R-134a refrigerant must never be mixed, even in the smallest of amounts, as they are incompatible with each other. If the
refrigerants are mixed, compressor failure is likely to occur. Refer to the manufacturer instructions included with the service equipment before servicing.
The air conditioning system delivers air that has been heated or cooled and dehumidified for occupant comfort. This system also provides the following
functions:
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Power ventilation
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Windshield defrosting
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Side window defogging
During most operating conditions, the blower motor takes in the outside air through the heater and air conditioning module assembly. Vehicle forward
movement forces in additional outside air.
Within the evaporator module, the blower motor pushes air through the evaporator, through the heater core, and then into the passenger compartment.
For air conditioning or defroster operation at ambient temperatures above 6°C (43°F), the refrigeration system chills the evaporator to almost freezing.
As air passes through the evaporator, the air temperature drops, causing the moisture in the air to condense on the evaporator core fins. This moisture
leaves the vehicle by gravity feed through a drain hole, dehumidifying the vehicle.
From the evaporator, some or all of the air may pass through the heater core, which is then warmed by the engine coolant. Any of the air that is not
heated mixes with the heated air before the air enters the passenger compartment.
When you select the maximum air conditioning mode, most of the air entering the blower motor is taken from the passenger compartment, or
recirculated. This air is most likely cooler than the outside air. All of the other modes use the outside air.
Cargo Van Rear Temperature And Mode Controls
A single front auxiliary HVAC control module located over the Instrument Panel (IP) controls the cargo van's auxiliary A/C air delivery and temperature
controls. Both temperature control and mode control for circulating the inside air is possible. The rear auxiliary mode valve directs air either through the
overhead vents or through the lower vents along the left side of the rear compartment. The rear auxiliary temperature valve directs the air flow either
through or around the heater core in the rear auxiliary ventilation system. Electric motors control the positions of both valves. Both the rear auxiliary
mode valve and seal assembly and the rear auxiliary temperature valve assembly receive operating voltage through CKT 341 (BRN) from RR HVAC
fuse 24. This voltage is available only when the ignition switch is in the START position or in the RUN position. Both valve assemblies ground through
CKT 150 (BLK) to ground G400. Each valve assembly positions in response to a voltage signal from the rear auxiliary HVAC control module. The rear
auxiliary mode valve and seal assembly receives the positioning signal through CKT 733 (LT BLU). The rear auxiliary temperature valve assembly
receives the positioning signal through CKT 734 (DK GRN). The rear auxiliary HVAC control module also receives power from RR HVAC fuse 24
through CKT 341 (BRN). The rear auxiliary HVAC control module also grounds through CKT 150 (BLK) to ground G401. In the control module,
current flows through 2 parallel rheostats. The temperature control dial moves the wiper arm of one rheostat. The mode control dial controls the wiper
arm of the other rheostat. The wipers select a portion of the voltage dropped across each resistance. The connected actuator motor receives this voltage
in order to position the valve.
Front Temperature Controls
The temperature valve actuator operates in response to a voltage signal from the heater and A/C controller's temperature control knob. When the ignition
switch is in the RUN position, operating voltage is available to the temperature valve actuator motor from HTR-A/C fuse 12 through CKT 141 (BRN).
The motor grounds to ground G201 through CKT 150 (BLK). The motor positions the air temperature valve in a position consistent with the voltage
signal from the heater and A/C controller. The actuator motor receives the signal in CKT 733 (LT BLU).
The heater and A/C controller also receives power from the HTR-A/C fuse 12 through CKT 141 (BRN). The heater and A/C controller also grounds
through CKT 150 (BLK) to ground G201.In the controller, current flows to ground through a rheostat. The temperature control moves the wiper arm of
the rheostat in order to select a portion of the voltage dropped across the resistance. The actuator motor receives the voltage in order to position the
valve.
Passenger Van Rear Temperature And Mode Controls
The passenger van's air delivery and temperature controls operate in a manner similar to the controls of the cargo van. The difference is the passenger
van has two control modules and an A/C control logic module.
The front auxiliary HVAC control module is over the IP. The rear auxiliary HVAC control module is overhead behind the front seats. The heater and
A/C control logic module is overhead, just ahead of the front auxiliary HVAC control module. The front auxiliary HVAC control module's blower switch
