System Tests - Volvo 850 Accessories Manual

Vacuum pump and regulator are contained in one unit, located
in left front corner of engine compartment. When cruise control system
is operating, a 12-volt electric motor pumps vacuum when accelerator
is depressed, sucking air out of tube which leads to vacuum servo. Air
is pumped out through right coupling. Each coupling is equipped with a
check valve to prevent air from entering tube via lower part of pump
housing.
Another tube provides constant atmospheric pressure to upper
pump housing. Regulator releases air to vacuum system when accelerator
is released.
VACUUM SERVO
Vacuum servo is located next to accelerator pedal and
consists of a housing and bellows. See Fig. 2. Bellows is pulled
toward housing when pressure decreases inside bellows, thereby pulling
on wire connecting throttle linkage and bellows.
ADJUSTMENTS
BRAKE & CLUTCH VALVES
Valves are self-adjusting. If manual adjustment is desired,
depress pedal until pedal arm does not make contact with valve. Pull
out plunger as far as possible and pull pedal up slowly. Plastic
catches in valve will hold piston in correct position.
VACUUM SERVO THROTTLE CABLE
Ensure throttle cable is taut at idle. Cable must not affect
position of throttle. See Fig. 2.

SYSTEM TESTS

NOTE: Diagnostic unit for retrieving codes is located in right
front section of engine compartment. Diagnostic unit is
equipped with an LED indicator, activation button and
function select cable. See Fig. 4.
All fault codes contain 3 digits (example 3-1-1). Since codes
have 3 digits, each code requires 3 series of flashes. A 3-second
interval separates series of flashes. Ensure all testing and diagnosis
is performed in the following order.