Pontiac Fiero 1988 Service Manual page 934

.1 Y E L
188
.8 Y E L 1 8 8
I-
.5 Y E L
V A C U U M J U N C T I O N
R E D
V A C U U M S O U R C E
A A
V E N T
M E C H A N I C A L
V A C U U M
V A L V E
V A C U U M S O U R C E
A A V E N T
S O L E N O I D
— 4 V A C U U M
V A L V E
S I N G L E DIAPHRAGM MOTOR
NO V A C U U M V A C U U M
3 W I R E S A R E SHOWN
C O N N E C T E D
T O G E T H E R WITH A
P I G G Y B A C K C O N N E C T O R
E A S Y FLOW
D I R E C T I O N
_r
T
V A C U U M
C H E C K
V A L V E
V A C U U M
T A N K
WHEN T H E V A L V E
IS IN T H E " A T R E S T "
POSITION, P O R T B
IS V E N T E D .
T H E V A C U U M A T
P O R T A HAS NO
E F F E C T .
WHEN T H E V A L V E IS M O V E D
TO T H E " O P E R A T E D " POSITION
V A C U U M F R O M P O R T A IS
C O N N E C T E D TO P O R T B
NO FLOW
D I R E C T I O N
D O U B L E DIAPHRAGM MOTOR
NO V A C U U M
T H E S O L E N O I D V A C U U M V A L V E
USES T H E S O L E N O I D TO M O V E
T H E V A L V E
Vacuum motors operate like electrical sole-
noids, mechanically pushing or pulling a shaft
between two fixed positions. When vacuum is
applied, the shaft is pulled in. When no vac-
uum is applied, the shaft is pushed all the way
out by a spring.
•
NO VACUUM
Double diaphragm motors can be operated
by vacuum in two directions. When there is no
vacuum, the motor is in the center "at rest"
position.
S E R V O MOTOR
P A R T I A L V A C U U M
Some vacuum motors such as the servo
motor in the Cruise Control can position the
actuating arm at any position between fully
extended and fully retracted. The servo is
operated by a control valve that applies vary-
ing amounts of vacuum to the motor. The
higher the vacuum level, the greater the retrac-
tion of the motor arm. Servo motors work like
the two position motors; the only difference is
in the way the vacuum is applied. Servo motors
are generally larger and provide a calibrated
control.