Vacuum System

A/C System Functional Test - Vacuum System

Vacuum Control System:

1. Engine at normal running temperature - Check that engine vacuum is at least 8-1/2 (Hg) inches.

2. With engine running, select 65 on TEMPERATURE SELECTOR. Wait 1 minute then select Defrost: DEFROST SCREEN OUTLETS should open and provide maximum hot air flow to screen. Air should have equal velocity from each side.

3. There should be a small air bleed to the footwells. Heavy flow indicates a fault with lower heater flap linkage or flap actuator.

4. Select AUTO at MODE CONTROL 65 at TEMPERATURE SELECTOR. Wait 5 minutes for camshaft to travel to full cooling mode and observe the following:

5. The center dash flap should open first and would indicate the vacuum system to this component is O.K. If it does not open, suspect mechanical seizure or vacuum supply fault.

6. Secondly, the heater water valve should close (observe arm movement - should be drawn fully into the unit). If this occurs, it demonstrates the camshaft vacuum switch, water valve and piping is in working order.

7. When the camshaft reaches the end of its travel to the full cooling mode position, the HI speed/Recirculation microswitch puts the fans in HIGH speed. The vacuum solenoid is also energized allowing a vacuum feed to the vacuum actuator on the blower casings placing the air inlet flaps in the recirculation mode. Check that flaps drop down to the fullest extent which indicates vacuum system O.K.

Failure to do this indicates either mechanical seizure or vacuum failure.


NOTE: When the vacuum supply is disconnected from any component, the component should return rapidly to its rest position. Also, bear in mind that the vacuum pipes may be perished, split or pinched causing complete failure or intermittent operation.