BMW TSB B64 11 92 (3569)
E31 850, E32 750 AC compressor shut down

Situation: AC compressor shuts down during heavy rain, or when driving thru deep standing water. The customer complant is loss of cooling. The condition disappears when engine is stopped and restarted.

Cause: The AC compressor clutch is disengaged by the slip monitoring function of the AC lock sensor control module. This module continiously monitors the engine speed and compares this to the AC compressor speed. The magnetic clutch of the compressor is automatically disengaged by the lock sensor module if the amount of slip exceeds 30%. The intent of this system is to prevent broken v-belt or reduced engine cooling if the AC compressor locks up. If the vehicle is driven in heavy rain or if standing water is spashed up into the engine compartment belt area, the v-belt and pulley may get wet enough to cause slippage in excess of 30%. The lock sensor control module perceives this as possible AC compressor lock up and opens the clutch circuit to prevent damage. The control module will remain in this state with the compressor clutch deactivated until the ignition is turned off and back on, clearing the condition.

Note: in addition to slip monitoring, an engine coolant temperature check has been incorporated into the lock sensor module on E32 vehicles produced since 09/1989, and E31 vehicles since the start of production. If engine coolant temperature rises above 240 degrees F., the AC compressor clutch is pulsed off at regular intervals to reduce engine load. If the coolant temperature rises above 250 degrees F., the clutch is switched off completely. As of 09/1992 production the slip monitoring fuction of the AC lock sensor module will be dropped on both E31 and E32 models.

Solution: If a customer complaint of AC cooling loss is received, the following items should be checked before proceeding with this repair:
-AC compressor belt tension adjusted to specification
-No oil leaks have contaminated the AC compressor belt, causing slip
-AC system pressure is within specificaion, not overloading compressor and belt.

If the above checks do not isolate the source of the slippage, proceed with the following repair. The remedy for this siwation varies with the model and production date of the vehicle. Refer to the appropriate ETM for diagrams showing connector, pin and control module locations.

750iL vehicles from the start of production thru 08/1989
Remove the lock sensor control module from the from the left hand side of the drivers footwell. The unit has 2 connctors, 4-pin and 5-pin and is located in the recesss of behind the kick panel.
Unplug the connectors X77 and X80 from the lock sensor control module body.
Remove pin 1 of connector X77 and pin 3 of connector X80 using a perminals removing tool.
Cut off the terminals and connect the loose wires with an insulated crimp connector. Shrink tubing may also be necessary to prvide proper insulation.
Tape or tie-wrap the loose wires with the other harness wires.
Plug the connectors back into the control module, reinstall the control module and reinstall the kick panel trim.

E32 750iL produced from 09/1989 thru 08/1991:
Remove the lock sensor control module from the left hand side of the drivers footwell, the unit also has 2 connectors, 4-pin and 5-pin.
Replace the lock sensor control module with p/n 61352233107 . This replacement module does not contain the slip monitoring function.
Reconnect the electrical connectors and install control module and kick panel trim.

E31 from start of production thru 08/1992:
E32 750iL vehicles produced from 09/1991 thru 08/1992:

Remove lock sensor control module from left side of driver's footwell. The unit has 1 connector with 10 pins and is loacted in the recess behind the kick panel.
Replace the lock sensor control module with p/n 61358360039 , this replacement module does not contain the slip monitoring function.
Reconnect and install....

Parts information:
lock sensor module 61358360039 10-pin type E31 from start thru 08/1992, E32 from 09/1991 thru 08/1992.

lock sensor module 61352233107 , 9-pin type, E32 from 09/1989 thru 08/1991

Warrantee status: parts and labour reimbursable.
Defect code: 64 52 07 12 00