Barometric Pressure Switch: Testing and Inspection

Fig. 34 Vacuum Switch:

OPERATION

1. While driving the vehicle at high altitudes, there is a tendency to accelerate more to make up for a lack of power.
2. When the vacuum of the intake manifold nears the atmospheric pressure (less than 60 mm Hg), the vacuum switch, Fig. 34, will turn off and signal to the control unit.
3. The control unit will then send a signal to the A/F solenoid of the carburetor to supply more fuel.

Fig. 35 Inspection Of Vacuum Switch W/Voltmeter:

TESTING ON THE VEHICLE

1. Run engine at idle.
2. Connect a voltmeter to the vacuum switch connector G terminal as in Fig. 35.
Voltage reading should be below 1.5V.
3. Disconnect the vacuum sensing tube from the switch, and then plug the tube.
Voltage reading should be approximately 12V.

Fig. 36 Applying Vacuum To Vacuum Switch And Checking Continuity:

TESTING OFF THE VEHICLE

1. Remove the vacuum switch.
2. Connect a vacuum pump to the vacuum switch Fig. 36.

Fig. 40 Vacuum Switch Continuity Chart:

3. Connect a circuit tester to the switch, and then check the continuity between the switch terminals Fig. 40.