Vacuum System Test
WARNING: This page is about a different car, the 1992 Lincoln Continental. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
A continuous hiss at control panel indicates a major vacuum leak somewhere in system. It does not necessarily indicate leak is at control panel.
- Start engine and depress control panel function buttons slowly from one position to another. A momentary hiss should be heard as each button is pressed. Hissing indicates vacuum is available at control panel.
- If hiss is not heard, check for a kinked, pinched or disconnected vacuum supply hose. Also inspect check valve between intake manifold and vacuum reservoir to ensure it is working properly.
- If momentary hiss is heard as each function button is pressed, vacuum is available at control panel. Cycle function buttons through each position with blower on high position, and check air discharge at ducts.
- If a vacuum motor fails to operate, airflow at ducts will be incorrect. See Fig 1 . If vacuum motor is inoperative, apply vacuum to motor. If motor operates, check vacuum hose (going to motor) for leaks or other damage.
- If vacuum system works normally at idle, but goes to defrost during acceleration, a small leak exists in vacuum system. Locate leak by shutting engine off and using a vacuum gauge to check for vacuum loss, while selectively blocking off vacuum hoses.