Express 1 Ton Van V8-5.7L VIN R (1999)
has an additional rear CNTL position. With the selection of the rear CNTL position, control of the rear auxiliary mode door is from the rear auxiliary
HVAC control module. With the front auxiliary HVAC control module in any other position, the rear auxiliary HVAC control module has no control.
Each control module receives power from RR HVAC fuse 24 through CKT 341 (BRN) when the ignition switch is in the RUN position or the START
position. Each control module grounds through CKT 150 (BLK) to ground G400. Each control module has a pair of rheostats for temperature and mode
control. The voltage developed at the wipers of these rheostats routes to the heater and A/C control logic module. CKT 734 (DK GRN) delivers the
temperature control signals. CKT 733 (LT BLU) delivers the mode control signals. If the front auxiliary HVAC control module is not in the rear CNTL
position, the relay in the heater and A/C control logic module remains de-energized. The signals from the front auxiliary HVAC control module then
route through the normally-closed contacts to the valve actuators.
When the front auxiliary HVAC control module is in the REAR CNTL position, a ground path is available fro the heater and A/C control logic module's
relay coil. Because the heater and A/C control logic module's relay coil receives voltage through CKT 341 (BRN) from RR HVAC fuse 24, current flows
through the relay coil, through CKT 203 (LT BLU) to the front auxiliary HVAC control module. Current then flows through the rear CNTL contacts in
the control module and continues to ground G400. The coil energizes. The contact change state in order to connect the positioning voltages from the rear
auxiliary HVAC control module to the valve actuators.
Vacuum System
Vacuum actuated doors regulate the airflow through the HVAC module. At various positions of the knob on the control assembly, mode doors mix and
direct cooled, heated, and outside air through the ducts.
In the event of vacuum line/harness leakage or hose collapse, you do not need to replace the entire vacuum harness assembly. Replace the vacuum
harness assembly by cutting the hose and inserting a plastic connector. If an entire hose must be replaced, cut the hose off at the connector, and then
attach a new hose directly to the vacuum solenoid control assembly.
