Important: To avoid misdiagnosis, complete Diagnostic Starting Point before beginning vacuum diagnosis.

1. Test 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 as necessary.
3. Reconnect all vacuum connections. Run the engine and cycle through the operating modes of the heater-A/C control while observing the valve actuators.

•	Test for vacuum to the mode valve actuators by noting the 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, test for vacuum leaks, collapsed vacuum hoses or binding valves. If OK, replace the heater-A/C control. Refer to Control Assembly Replacement .