A/C Compressor Control: Notes

Activation of the compressor clutch is an output control function of the IHKA module. As with the E38 IHKA, activation is carried out directly through a final stage in the module (no relay required).

The signals KO and AC have been combined into one signal providing multiple data through a stepped increase in signal duty cycle.

Fig 1: Identifying A/C Compressor Control Function

Courtesy of BMW OF NORTH AMERICA, INC.

SIGNAL KO: 

• 15% Duty Cycle: IHKA is OFF.
• 30% Duty Cycle: IHKA is switched ON (Standby).
• 45% Duty Cycle: Snowflake button is pressed, the IHKA signals the engine control module to raise the idle speed in preparation of the compressor being switched on. This takes place before the IHKA energizes the compressor.