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

1. Inspect the vacuum supply to the vacuum/electric solenoid (purple and black vacuum hoses) while the engine is running:

•	The vacuum should be approximately 124 kPa (18 psi) with the engine running.

•	The vacuum should remain at approximately 124 kPa (18 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 and electrical connections.
4. Start the engine. 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 the vacuum actuator retracts incorrectly, replace the heater-A/C control. Refer to Control Assembly Replacement .

•	If the vacuum actuator does not retract, inspect for vacuum leaks, collapsed vacuum hoses or binding valves. If the vacuum actuator is OK, replace the vacuum/electric solenoid.