900 L4-1985cc 2.0L SOHC (1988)
Compressor HVAC: Description and Operation
Compressor And Radiator Fan Motor 37
The AC can be switched on and off by means of AC switch 169, which is supplied from fuse 6, via the 29-pole black connector 152C. When the switch
is depressed, the lamp built into the button will be supplied directly (not via the resistor), so it will light up with full intensity. (When the switch is not
activated, the lamp is supplied from the instrument lighting rheostat.)
Compressor 170 and ordinary radiator fan 37 are connected via relay 156, whose contacts are supplied from fuse 25. The relay will be energised when
the following conditions are satisfied:
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Pressure switch 166 is closed, i.e. the refrigerant pressure is at least 2.8 bar.
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Anti-freeze thermostat (cycling clutch contact) 171 is closed, i.e. the ambient temperature is at least about +6 °C.
When the relay is energised, the compressor will be supplied only if temperature switch 168 is closed. (The switch will open if the engine temperature
exceeds around +115 °C.)
Diode 173, which is connected in parallel with the compressor, reduces the voltage transients at the instant when the compressor is switched off.
Delayed connection when starting:
Relay 156 is equipped with two time delay functions. One of them is activated whenever the engine is being started. Ignition switch 20 (in the start
position) supplies pin 50, and if switch 169 is then depressed, the energising of the relay and thus starting of the compressorwill be delayed for around
10 seconds, to avoid an excessive load on the battery.
AC Radiator Fan 172
Extra radiator fan 172 for the AC is connected via relay 155 and is supplied from fuse 6.
The relay coil is supplied from the contacts of relay 156 and from pressure switch 166. The AC radiator fan thus runs when AC switch 169 is depressed
and pressure switch 166 is closed.