Saab 900 Service Manual page 110

854-98 Heating and ventilation systeni,air conditioning system
Cycling clutch system, 1980 models
The magnetic clutch of the compressor is
supplied from fuse 18 (16A) in the electrical dis-
tribution box. The circuit includes one normally-
open and two normally-closed contacts. The cir-
cuit is earthed across a pressure-sensing switch
on the high-pressure side of the compressor.
When the air distribution control is set to AC
max., AC fresh or defroster, a vacuum switch
(169) will close the circuit. At the same time, the
AC relay (155) will close, thus starting the extra
radiator fan (37).
In the case of an AC installed as an accessory
(not U.S.A., Canada), a switch (164) is fitted in-
stead of the vacuum switch (169). The switch
(164) is mounted in the facia and enablesthe AC
to be started and stopped, regardless of the set-
ting of the air distribution control.
The thermostat switch (165) which is integrated
into the anti-frost thermostat senses the temper-
ature at the evaporator outlet and regulates the
operation of the compressor clutch.
A time relay (167) (only fitted in cars with
automatic transmission), which .is activated by
throttle switch (137), breaks the circuit for about
20 seconds when the throttle opening is exces-
sive. In otherwords,·it isolates the compressor to
avoid loss of power during acceleration. A ther-
mocontact (168) which senses the temperature
ofthe coolant is connected across the circuit.and
is primarily intended to ensure that the engine
receives adequ?lte cooling. If the temperature
goes above 115°C (230°F), the thermocontact
will break the circuitto the compressor's magne-
tic clutch.
A device (142) which increases the idling speed
of the engine is connected in parallel with the
magnetic clu'tch circuit. This device consists of a
solenoid which' boosts the supply of air to the
inlet manifold.
An over-pressure switch (166), which senses the
pressure in the high-pressure side ofthe system,
is connected in parallel with the ordinary cooling
system's thermocontact (39) for the rad iator fan
motor. When the pressure in the system reaches
a predetermined level the contact closes and the
radiator fan is started.
Saab900
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