IHKA/ECM Interfaces
The IHKA signals the ECM when A/C is requested (KO signal), this alerts the ECM to stabilize idle speed (EML on 750iL) and compensate for the additional load. This signal is Pulse Width Modulated (5 Hz), which informs the ECM of the "get ready" request and the anticipated compressor load. On the 99 MY (E38/39/46), the A/C on signal is transmitted via the K-Bus/CAN-Bus.
On E38/39 models, the ECM sends a reply (KOREL) signal to the IHKA control module. If input conditions are correct, the IHKA will activate the A/C compressor. In addition this separate signal circuit is used to signal the IHKA to deactivate the compressor in the event that stand still full load conditions are present.
On E46/36 models, the A/C compressor relay is activated by the ECM.