Vacuum System Test

WARNING: This page is about a different car, the 1995 Pontiac Grand Prix and 1995 Oldsmobile Cutlass Supreme. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Before performing this test, perform OUTLET AIRFLOW INCORRECT test.

Start engine. Check vacuum supply to solenoid box (Black vacuum hose). Vacuum should be about 18 psi (1.2 kg/cm² ) and remain at 18 psi (1.2 kg/cm² ) when engine is turned off.
Check each vacuum actuator by disconnecting vacuum hose and applying vacuum directly to actuator. Repair or replace actuator as necessary. See Fig 1.
Reconnect all vacuum and electrical connections. Run engine and cycle through all A/C-heating modes while observing vacuum actuators. Check for vacuum to vacuum actuators by observing vacuum actuator position. When vacuum is applied, actuator will retract.
If an actuator retracts when it should not, replace A/C-heater control assembly. If an actuator does not retract, check for vacuum leaks, collapsed vacuum hoses or binding valves. If components are okay, replace solenoid box.

Fig 1: Air Delivery Vacuum Distribution Chart

Courtesy of GENERAL MOTORS CORP.