Compressor Clutch

WARNING: This page does not describe the selected car, but rather 41 other vehicles, including the 2003 BMW M5, 2003 BMW M3, 2003 BMW 540i, 2003 BMW 530i, and 2003 BMW 525i. However, it is still accessible from the selected car via links, so may be relevant.

The compressor pulley is driven by a belt from the crankshaft; a compressor clutch is used to engage/disengage the pulley and driveshaft. The clutch is electromagnetic. When power is provided to the clutch, the clutch engages and rotates the compressor drive shaft. When the power is cut off, the clutch disengages and the compressor pulley freewheels. On BMW A/C systems, the compressor is cycled on and off, according to evaporator temperature; it is also cycled off at full-throttle, standing start acceleration conditions.

Fig 1: Identifying Compressor Clutch

Courtesy of BMW OF NORTH AMERICA, INC.

A diode is used to prevent induced current and voltage from damaging the control module/relays when the clutch solenoid is disengaged. The diode allows the voltage spike created when the clutch solenoid is disengaged, to flow in a loop back through the solenoid coil, until the energy is dissipated. Different vehicles use different control modules to control the compressor clutch.

Fig 2: Identifying Control Modules To Control Compressor Clutch Circuit

Courtesy of BMW OF NORTH AMERICA, INC.

The compressor clutch is unit replaceable.