Pontiac FIREBIRD 1972 Service Manual page 1426

ACCESSORIES 15-1 1
/WIRE RELIEF LUG
TURN S I G N A L LEVER
- 4
R E T A I N I N G
d
Fig. 15-8 Turn Signal Lever and Engagement Switch
With the solenoid valve winding energized, the valve will
pull up off its seal allowing engine vacuum to enter the
regulator passage and be passed to the servo.
In this position, current also passes to the solenoid valve
frame and through the coupling coil winding to ground.
With the coupling coil energized, the vacuum regulator
plate is engaged. The regulator plate is now mechanically
connected to the governor, regulating the size of the vent
opening.
Now when the engaging switch is released, the contact at
B is broken but A remains complete through the switch,
thus keeping the coupling coil and solenoid valve ener-
gized. Current now flows from the ignition switch through
the fuse block and brake switch to the No. 2 terminal of
the connector at the regulator. In the full up position, the
solenoid valve makes contact with its frame, passing cur-
rent through the frame and through the coupling coil.
Enough current passes from the solenoid frame. through
the solenoid winding to hold the valve up, although not
enough to pull it up once it is released. The driver's speed
is now automatically regulated.
The electrical circuit can be broken by the driver in three
different ways. He may turn off the ignition switch or step
on the brake (open the brake switch), thus the feed circuit
to the engagement switch would be broken. It is also
possible for the driver to disengage the Cruise Control by
pressing in and holding the engaging switch. This will
open both circuits at A and B. The only time the button
CABLE
CONNECl
VACUUM
FROM
REGULATOR
Fig. 15-9 Vacuum Servo
would be held in this position is when the driver wants to
change the speed setting of the Cruise Control downward.
Release of the button once again gives the driver auto-
matic speed control at his new speed.
When the brake pedal is depressed, the vacuum release
switch immediately vents the vacuum hose to the servo.
This renders the system inoperative independently of the
electrical circuit.
VACUUM SERVO
The vacuum servo (Fig. 15-9) is located on the left hand
fender skirt. It is connected through a cable to the throttle
lever and varies throttle opening in relation to vacuum
supplied by the regulator.
VACUUM SOURCE
\
VACUUM TO SERVO
CENTERING' SPRING
ADJUSTMENT SCREW
Fig. 15-10 Regulator Assembly