Vacuum System

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

Start the engine and allow it to idle. Move the rotary knob to each position and refer to the vacuum diagrams and operational charts for airflow, air door functioning, and vacuum circuits. If airflow is not out of the proper outlet at each rotary knob position do the following:

Inspect
1. The hose connections at the vacuum actuator's, control head valve, and vacuum tank.

Vacuum Schematic:

2. The vacuum source circuit:
- Install a vacuum tee and gauge (with restrictor) at the vacuum tank outlet. Idle the engine and read the vacuum. At all selector lever positions, normal vacuum is equivalent to manifold vacuum.
- If vacuum is less than normal at all positions, remove the tee and connect the vacuum gauge line to the tank and read the vacuum. If still low, then the problem lies in the feed circuit, the feed circuit to the tank or in the tank itself. If vacuum is now normal, then the problem lies downstream.
- Vacuum may be less than normal at some positions. If vacuum was low at one or several of the selector lever positions, a leak is indicated in these circuits.
- Vacuum may be normal at all positions. If vacuum was normal and even at all positions, then the malfunction may be caused by improperly connected or plugged or split lines or a malfunctioning vacuum valve or valves.
3. Specific vacuum circuit check:
- Place the rotary knob in the malfunctioning position and check for vacuum at the pertinent vacuum actuator's.
- If vacuum exists at the actuator but the door does not move, then the actuator is defective or the door is mechanically bound.
- If low or no vacuum exists at the actuator, determine whether the cause is the vacuum harness or the vacuum valve.
- Check the vacuum harness first.

Vacuum Harness Routing:

Vacuum Harness To The Rotary Valve:

Vacuum Harness To The Air Inlet Valve:

4. Vacuum harness circuit check:
- Disconnect the vacuum harness at the control head.
- The gray line should show engine vacuum. If not, trace back through the connector to the vacuum tank.
- To check any individual circuit, place the selector lever at the involved circuit position and check for vacuum.