M70 AC Compressor Shutdown - lock sensor control info
The M70 AC compressor has a lock sensor. The air conditioning compressor clutch is disengaged by the slip monitoring function of the Air Conditioning Lock Sensor Control Module. This module continuously monitors engine speed and compares this to the air conditioning 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 air conditioning compressor locks up.If the vehicle is driven in heavy rain, or if standing water is splashed up into the engine compartment belt area, the V-belt and pulleys may get wet enough to cause slippage in excess of 30%. The lock sensor control module perceives this as possible air conditioning compressor lockup, 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.

Group 64 Heating and Air Conditioning B 64 11 92 (3569) Woodcliff Lake, NJ Product Engineering June 1992 SUBJECT: Air Conditioning Compressor Shutdown

MODEL E31, E32 75OiL
Situation: Air conditioning shuts down during heavy rain, or when driving through deep standing water. The customer complaint is loss of cooling. The condition disappears if the vehicle is stopped and restarted.
Cause: The air conditioning compressor clutch is disengaged by the slip monitoring function of the Air Conditioning Lock Sensor Control Module. This module continuously monitors engine speed and compares this to the air conditioning 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 air conditioning compressor locks up.If the vehicle is driven in heavy rain, or if standing water is splashed up into the engine compartment belt area, the V-belt and pulleys may get wet enough to cause slippage in excess of 30%. The lock sensor control module perceives this as possible air conditioning compressor lockup, 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 control module on E32 vehicles produced since 9/89, and E31 vehicles since the start of production. If engine coolant temperature rises above 240 degrees F, the air conditioning 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 9/92 production, the slip monitoring function of the Air Conditioning Lock Sensor Control Module will be dropped on both E31 and E32 models.
Solution: If a customer complaint of A/C cooling loss is received, the following items should be checked before proceeding with this repair:
A/C compressor belt tension adjusted to specifications
No oil leaks have contaminated the A/C compressor belt, causing slip
A/C system pressure is within specification, 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 situation varies with the model and production date of the vehicle. Refer to the appropriate ETM for diagrams showing connector, pin, and control module locations.

#1 75OiL vehicles from start of production through 8/89:
Remove the Lock Sensor Control Module from the left hand side of the driver's footwell. The unit has two connectors (4 pin and 5 pin) and is located in the recess 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 terminal removal tool.
Cut off the terminals and connect the loose wires with an insulated crimp connector. Shrink tubing may also be necessary to provide proper insulation.
Tape or tie-wrap the loose wires to the other harness wires.
Plug the connectors back into the control module, reinstall the control module, and reinstall the kick panel trim.

#2 75OiL vehicles produced from 9/89 through 8/91:
Remove the Lock Sensor Control Module from the left hand side of the driver's footwell. The unit has two connectors (4 pin and 5 pin) and is located in the recess behind the kick panel.
Replace the Lock Sensor Control Module with P/N 61 35 2 233 107. This replacement module does not contain the slip monitoring function.
Reconnect the electrical connectors and install the control module. Reinstall the kick panel trim.

#3 E31 vehicles from start of production through 8/92:
75OiL vehicles produced from 9/91 through 8/92:
Remove the Lock Sensor Control Module from the left hand side of the driver's footwell. The unit has one connector (10 pin) and is located in the recess behind the kick panel.
Replace the Lock Sensor Control Module with P/N 61 35 8 360 039. This replacement module does not contain the slip monitoring function.
Reconnect the electrical connector and install the control module. Reinstall the kick panel trim.
Parts Information :
Lock Sensor Module 61 35 8 360 039
(10 Pin type: E31 from start through 8/92,
E32 from 9/91 through 8/92)
Lock Sensor Module 61352233107 (9 Pin type: E32 from 9/89 through 8/91)
Warranty Status parts and labor reimbursable under the terms of the applicable BMW New Car Limited Warranty. Defect Code 64 52 07 12 00