In the above vehicles, incorrect service programming or incorrect coding could cause the air-conditioning compressor to no longer be activated.
The signal of the activating/deactivating switch for the air-conditioning system is forwarded to the electric system control unit. This control unit communicates with the engine control unit via the CAN bus. The compressor coupling relay is driven by means of the engine control unit. A diagnostics tool can not only read out the event memory, but can also check the function of the magnetic coupling by means of an actuator test. In addition, the diagnostics tool can "recognize" in what way the activating and deactivating signal of the switch arrives at the control unit.
If the fuses and wiring are OK, the activation circuit of the magnetic coupling and the switch have been checked, and the control unit does not contain any system-relevant error codes, then it may be possible to correct the problem by repeating the coding/service programming of the control unit. This should be performed by an authorized dealer.
Important safety note