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 H29-3 or 33-pole blue connector H33-3. 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 via fuse 6.)

Compressor 170 and ordinary radiator fan are connected via relay 156, whose contacts are supplied from fuse 25. The relay will be energized when the following conditions have been 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 energized, power will be supplied to the compressor only if temperature switch 168 is closed. (The switch will open if the engine temperature should exceed about +115 °C.)

Delayed Connection When Staring
Relay 156 is equipped with two time delay functions. One of these is activated whenever the engine is started. Ignition switch 20 (in the start position) supplies pin 50, and if switch 169 is then depressed, the energizing of the relay and thus starting of the compressor will be delayed by about 10-20 seconds (depending on the engine variant), to ensure that combustion in the engine will be stable after starting, before the AC load is applied.

Idling Speed Compensation and Cut-out at Full Load

Cars without AIC valve
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.

Cars with AIC valve
On certain variants, 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 14 when the time delay of the relay is activated, and it then starts idling speed compensation. After 0.3 seconds, the relay will be energized and the compressor will start. The relay electronics receive their supply (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 angled transmitter 203, and the relay will trip the compressor.