With Time Delay

Operation

Compressor 170 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 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:

- Pressure switch 166 is closed, i.e. the refrigerant pressure is at least 2.8 bar.

- 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 should exceed about +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 compressor will be delayed for about 10 seconds, to ensure that combustion in the engine will be stable after starting, before the the AC load is applied.

Idling Speed Compensation And Cut-Out At Full Load

8-valve 900 and 16-valve 900 without catalytic converter

Auxiliary air valve compensates for frictional losses in conjunction with starting from cold, by by-passing air at the throttle butterfly.

Solenoid valve 142, which is kept open when the compressor is running, is used for idling speed compensation for the increased load caused by the AC.

16-valve 900 with catalytic converter

On cars with catalytic converter, the auxiliary air valve is replaced by an Automatic Idling Control (AIC) valve which also compensates for instantaneous load increases at idling speed.

The control unit receives a signal via relay pin 16 when the time delay of the relay is activated, and it then starts idling speed compensation. After 0.3 seconds, the relay will be energised and the compressor will start. The relay electronics are supplied (in the drive position) via pin 15.

When the engine is running at full throttle, pin TK of the relay will be earthed through throttle angle transmitter 203, and the relay will trip the compressor.

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.

Recirculatlion Valve 38
Recirculation valve 38, which controls the recirculation damper, will be switched on when recirculation switch 143 is depressed. The switch is supplied from fuse 6. When the switch is depressed, the lamp built into the switch will light up with full intensity.

The recirculation valve is also connected across main switch 149, when the air distribution control is in position 0 or < - > (regardless of the position of switch 143). The supply is taken from fuse 9, via ventilation fan resistor 74.