Saab 900 Service Manual page 106

854-94 Heating and ventilation system, air conditioning system
The electrical system
VIR system
The magnetic clutch of the compressor is
supplied from fuse 18 in the electrical distribu-
tion box. The circuit includes one normally-open
and three normally-closed contacts and a fuse.
On cars with automatic transmission, the same
circuit also contains a time-delay relay with nor-
mally-closed contacts. If the air distribution con-
tro I is set to AC max., AC fresh or defroster, a vac-
uum switch (169) will close the circuit. A
temperature switch (165) which senses the in-
coming air temperature will open the circuit ifthe
air temperature is below about +3°C. A time
relay (167) (only fitted in cars with automatic
transmission), which is activated by throttle
switch (137). breaks the circuit for about 16 se-
conds when the throttle opening is excessive. In
other words, the compressor is isolated to avoid
loss of power during acceleration. A thermocon-
tact (168) which senses the tem perature of the
coolant is connected across the circuit and is
primarily intended to ensure that the engine re-
ceives adequate cooling. If the tem'perature
goes above 230°F (115°C), the thermocontact
will break the circuit to the compressor's magne-
tic clutch.
An over-pressure cut-out (164), activated by the
pressure in the high-pressure side ofthe system,
breaks the circuit if the pressure exceeds 350 Ib/
in
2
(25 kglcm
2
)
for any reason. A temperature-
sensitive switch in the compressor closes if the
temperature in the compressor becomes exces-
sive. This. switch loads a fuse (162) in the
magnetic clutch circuit which blows, breaking
the circuit. Blown fuses must be replaced.
A device (142) which increases the idling speed
of the engine is connected in parallel with the
magnetic clutch circuit.., On _ fuel injection en-
gines this consists o(a"so'lenbid which boosts
the supply of airto the inlet manifold and, on car-
burettor engines, a solenoid which activates the
throttle.
An over-pressure switch (166) which senses the
pressure in the high-pressure side of the system
is connected in parallel with the ordinary cooling
system's thermocontact (39) for the radiator fan
motor. When the pressure in the system reaches
a predetermined level the contact closes and the
radiator fan is started.
Saab900