Important: In order to avoid misdiagnosis, complete Diagnostic System Check before beginning the vacuum diagnosis.

1. Inspect the vacuum supply to the mode selector (purple and black vacuum hoses) while the engine is running.

•	Vacuum should be approximately 83 kPa (12 psi) with the engine running.

•	Vacuum should remain at approximately 83 kPa (12 psi) when the engine is turned OFF.

2. Test each vacuum actuator by disconnecting the vacuum hose and applying vacuum directly to the actuator. Repair or replace a vacuum actuator as necessary.
3. Reconnect all of the vacuum connections. Run the engine and cycle through the operating modes of the heater-A/C control while observing the valve actuators.

•	Inspect for vacuum to the mode valve actuators by noting mode valve actuator position. When vacuum is applied, the actuator will retract, refer to the Air Delivery Vacuum Distribution table below.

•	If a vacuum actuator retracts incorrectly, replace the heater-A/C control. Refer to Control Assembly Replacement .

•	If a vacuum actuator does not retract, inspect for vacuum leaks, collapsed vacuum hoses, or binding valves. If these components are OK, replace the heater-A/C control. Refer to Control Assembly Replacement .