Subaru XT 1988 Service Manual page 1262

6-2 BODY ELECTRICAL SYSTEM
CONSTRUCTION OF VACUUM SYSTEM
Hose
Valve ASSY
valve
Eccentric
shaft
Fig. 82
1) Pump
The pump is controlled by the vacuum switch built into the
valve ASSY tank, and is used to supply vacuum to the tank.
Power to the pump is fed when the vacuum switch is turned
ON, and the diaphragm is moved up and down by the rotation
of the offset shaft fixed to the motor shaft.
2) Valve ASSY
The vacuum valve, vent valve, and safety valve are provided,
and their open-close operation lead vacuum/atmospheric
pressure to actuator. Also to attached to this assembly is the
tank for storing vacuum generated by the pump, and the
vacuum switch for controlling the pump to maintain a con-
stant vacuum level in the tank.
If the cruise control is turned on and a constant car speed
is attained, the safety valve connected to the atmosphere is
closed. Also, the vacuum valve connected to the tank and the
vent valve connected to the atmosphere operate to lead the
atmosphere/vacuum to the actuator. When the cruise control
is cancelled, the vacuum valve closes to shut off the tank
vacuum, and the safety valve opens to allow atmospheric
pressure to enter the actuator.
52
Actuator
Diaphragm
To engine
throttle
L6-566
The vacuum in the tank is consumed by the operation of the
vacuum valve. If the vacuum in the tank reaches
-42.7
kPa
(-320
mmHg,
-12.60
inHg) the vacuum switch is turned ON,
and the pump feeds the vacuum into the tank. When the
vacuum in the tank reaches
-50.7
kPa
(-380
mmHg,
-14.96
inHg) the vacuum switch turns OFF to stop the pump.
Signal from control unit and valve operation
Safety
Vacuum Vent
valve
valve valve
System OFF Open Close Open
Memory
<
actual
Close Close Open
car speed
System Memory = actual
Close Close Close
ON car speed
Memory
>
actual
Close
Open
Close
car speed