Compressor Control (750iL)

IHKA E32 COMPRESSOR CONTROL (750iL)







M70 V-12 compressor control is similar to that on six cylinder vehicles, but some additional components and circuitry are placed between the compressor control relay and the A/C compressor.

On 750iL vehicles produced through August 1989, the relay passes the A/C request to the lock-sensor control module. This module monitors two key inputs in order to decide whether or not to turn on the A/C compressor clutch. These inputs are:
- A/C compressor RPM (sensor in compressor)
- Engine crankshaft RPM (TD signal from the engine control module)

If the two rotating speeds differ by more than 30%, the lock-sensor control module assumes that the A/C compressor is slowing or seizing, and it interrupts power to the clutch. Power remains interrupted until the Ignition Switch is cycled.







Beginning in September 1989, the M70 V-12 lock-sensor control module also monitors engine coolant temperature. If it exceeds 240 °F (117 °C), the lock-sensor control module cycles the A/C compressor on and off (20 seconds on/20 seconds on), to reduce engine load. Above 250 °F (120 °C), the lock-sensor control module shuts off the A/C compressor.


NOTE: On vehicles produced from September 1992, the lock-sensor control module no longer monitors A/C compressor and engine crankshaft speeds for slippage.