COMPRESSOR CONTROL
Control of the A/C compressor is a function of the Engine Control Module as in the E36.
However, the control has changed to include the regulated auxiliary fan operation.
Pressing the snowflake button is a request for A/C activation. As long as the evaporator
temperature is Above 36° F, the IHKA will signal the DME control module to activate the
compressor.
The IHKA control module sends the following signals to the DME over the K-Bus and CAN
Bus via the instrument cluster:
• Request for A/C activation (signal KO)
• Load torque for switching the compressor on
• Requested auxiliary fan speed
The IHKA determines the load torque for compressor activation and required auxiliary fan
speed from the pressure sensor mounted on the receiver/dryer.
The pressure sensor provides a linear voltage input signal (0 - 5 volts) to the IHKA control
module. The IHKA processes this signal and determines the load torque of the system (0
to 30 Nm with a variable displacement compressor). The higher the pressure in the system,
the higher the voltage input signal to the IHKA.
The output signal to the DME will enable the engine control module to modify the idle
speed, timing and fuel injection amount based on the load that will be imposed when the
compressor is activated.
The auxiliary fan is now a variable speed fan (15 stages) based on the system load. The
DME will activate the fan through a pulse modulated final stage control.
8
E46 Climate Control
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