A/C Signal: Description and Operation

AIR CONDITIONING:
When the air-conditioning system is switched on, the heating/air-conditioning control unit sends a signal to the DME control unit (terminal 69). The size of the signal depends on the current power consumption of the air-conditioning compressor and results in changes in the basic air quantities which the DME control unit supplies to the engine using the idle air control valve.

The DME control unit then sends a signal to the air-conditioning relay via terminal 62, this closes and connect the compressor coupling.
The following conditions must apply before the air-conditioning relay is actuated:
- Engine temperature between 3 and 117°C
- Intake air temperature > 3°C
- Time after engine start > 5 seconds

Additional Function:
If, when the air-conditioning system is switched on, the engine undergoes heavy acceleration, the compressor is switched off for 15 seconds.

If the AC button is actuated and the engine started, the air-conditioning relay is not activated until the system detects that the engine is running.

If an automatic exhaust emission test is carried out, the air-conditioning compressor switches off.

If the DME control unit performs the tank venting diagnosis, the current compressor status is retained for the duration of the diagnosis.

Pressure Switch:
The air-conditioning system pressure switch closes with pressures > 16 bar. Ground potential is applied to the DME control unit via terminal 14. As a result, the radiator fan is switched to speed 2 when the engine is running.