With RPO C67

CIRCUIT DESCRIPTION
AIR DELIVERY
With the ignition switch in "RUN," voltage is applied through I/P fuse #20 to the H-A/C control. The operating mode of the system is determined by buttons on the front panel. Ground signals determine which air valves are to be operated as well as the position of the temperature valve.

The vacuum/electric solenoid contains the solenoid valves that control the vacuum actuators. When the solenoids are de-energized, the valves vent the vacuum actuators, allowing the vacuum actuator to return to the vent position.

AIR DELIVERY
H-A/C CONTROL
With the ignition switch in "RUN," voltage is applied through I/P fuse #20 to the H-A/C control. The operating mode of the system is determined by buttons on the front panel. Ground signals determine which air valves are to be operated as well as the position of the temperature valve.

VACUUM/ELECTRIC SOLENOID
The vacuum/electric solenoid contains the solenoid valves that control the vacuum actuators. When the solenoids are de-energized, the valves vent the vacuum actuators, allowing the vacuum actuator to return to the vent position.

RECIRCULATION VALVE
The recirculation valve closes off most of the outside air inlet, so that the air from the inside of the vehicle is recirculated through the A/C system for maximum cooling. The outside air inlet is partially closed when vacuum is applied to the actuator. When the air inlet valve actuator is vented, the recirculation valves close off the in-car air inlet which allows outside air to be drawn into the vehicle.

DEF/HEATER
The DEF/heater valve determines whether air flow will be directed to the windshield defrost outlets. With vacuum applied to the gray hose at the defroster valve actuator, the valve is positioned to allow air flow to the windshield defrost outlets, with some bleed to the heater outlet.

UPPER/LOWER MODE
The upper/lower mode valve can assume three positions and is operated by a bi-directional vacuum port which can move the valve to either of two positions. If no vacuum is applied to either vacuum port, the valve is in mid-position. Air flow with the valve in mid-position will he delivered to the panel outlets and the floor outlets (Bi-Level). When the upper/lower solenoid (#3) (tan vacuum hose) is operated, the valve is positioned to direct air flow to the A/C outlets. When the upper/lower solenoid (#4) (red vacuum hose) is operated, the valve is positioned to direct air flow to the heater outlets and defroster outlets.

DIAGNOSTIC AIDS
1. Make sure that ground G200 is clean and tight.
2. Check I/P fuse 20. If open, check for a short to ground in CKT 241.
3. Check for normal operation of engine vacuum check valve.
With engine warm and running in idle:
4. Check manifold vacuum at the black hose from the engine to the vacuum tank.
5. Check for vacuum at the violet hose from the vacuum tank to the electric solenoid.
6. Check that the vacuum hoses from the electric solenoid to the vacuum actuators are connected and in good condition.
7. Check for a broken (or partially broken) wire inside of the insulation which could cause system failure but prove "GOOD" in a continuity/voltage check.
8. Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems.

VACUUM DIAGNOSIS
1. Check vacuum supply to vacuum/electric solenoid (black vacuum hose) while engine is running.
^ Vacuum should be approximately 38 to 43 cm Hg (15 to 16 inch Hg) with engine running.
^ Vacuum should remain at approximately 38 to 43 cm Hg (15 to 16 inch Hg) when engine is turned off.
2. Test each vacuum actuator by disconnecting the vacuum hose and applying vacuum directly to the actuator. Repair or replace as necessary.
3. Reconnect all vacuum and electrical connections. Run engine and cycle through the operating modes and full temperature range of the H-A/C control while observing the vacuum actuators.
^ Check for vacuum to the vacuum actuators by noting vacuum actuator position. When vacuum is applied, the actuator will retract, refer to image above.
^ If a vacuum actuator retracts when it should not, replace the H-A/C control, after performing the diagnostics on Chart.
^ If a vacuum actuator does not retract when it should, check for vacuum leaks, collapsed vacuum hoses, binding valves or bad connections at the vacuum/electric solenoid. If OK, replace the vacuum/electric solenoid.