Vacuum System

Ports on rotary vacuum valves are illustrated to provide simplicity when following vacuum schematic lines. The ports are numbered in consecutive order on the actual valve.

1. Start the engine. Let the engine idle.




Check each position of the rotary knob. Use the vacuum diagrams in order to check the following functions:
- The airflow
- The air door functioning
- The vacuum circuits
2. If an air outlet is not working, inspect the hose connections at the vacuum actuator's control head valve and at the vacuum tank.
3. Inspect the vacuum source circuit. Execute the following operations:
- Install a vacuum tee at the vacuum tank outlet. Use a gauge with a restrictor. Idle the engine and read the gauge. A normal vacuum is equivalent to the manifold vacuum at all positions on the selector lever.
- If the vacuum is insufficient at all positions, remove the tee. Connect the vacuum gauge line to the tank. Check the gauge reading. If the vacuum remains low, the problem is at one of the following locations:
- The feed circuit
- The feed circuit to the tank
- The tank
- If the vacuum is now normal, the problem is downstream.
- The vacuum may be less than normal at some positions. A leak exists in these circuits.
- If the vacuum is normal at all of the positions, the malfunction may be caused by one or more of the following conditions:
- Improper connections
- Plugged lines
- Split lines
- Malfunctioning vacuum valves
4. Inspect the vacuum circuit:
1. Place the rotary knob in the malfunctioning position.
2. Inspect for vacuum at the pertinent vacuum actuator.
3. If a vacuum exists at the actuator but the door does not move,the actuator is defective or the door is jammed.
4. Vacuum is low or nonexistent at the actuator. First check the vacuum harness. Check the vacuum valve.
5. Inspect the vacuum harness circuit:
- Disconnect the vacuum harness at the control head.
- The gray line should show engine vacuum. If not, trace the gray line back through the connector to the vacuum tank.
- In order to inspect individual circuits, place the selector lever at the proper circuit position. Inspect for vacuum.