750 lock sensor 3 pins compressor vs 1 pins compressor - my research
Author: Johan750 Posted on: 2013-01-17
As the pump in my 750 seems to leak uv dye around the compressor seal I got myself a new one. Later I saw the new one has only 1 connection in the electrical plug and thus missing the speed signal. And of course no where to mount it so I can't transplant is. So I did some schematics checking and came up with the following:
There are two types of lock sensors. The first one was used with the R12 upto 09/91. The second after that with R134a. As these have different plugs they don't "officially" interchange.
The part numbers of the old/R12 one in order they apeared:
61 35 1 382 833
61 35 1 388 718
61 35 1 390 899
The part numbers of the new/R134a one in order they apeared:
61 35 1 392 410
61 35 8 360 039
The pin-out of the first type (two connectors):
x80-1 -- BL - to compressor rpm sensor
x80-2 -- BL/BR - to compressor rpm sensor
x80-3 -- SW/RT/GE - 12v from compressor relay
x77-1 -- SW/GR - To compressor clutch
x77-2 -- GN/BL/GE - 12v in Run/Start Fuse 29
x77-3 -- BR/SW - ground
x77-4 -- SW - to DME, EML,..etc. engine rpm
The pin-out of the second type (one connector):
x9988-2 -- BR/SW - Ground
x9988-3 -- SW/RT/GE - 12v from compressor relay
x9988-4 -- GN/BL/GE - 12v Run/Start Fuse 29
x9988-5 -- SW/GR - to compressor clutch
x9988-7 -- BR/GE - tap on cluster (x16-24) engine temp sensor
x9988-9 -- BR/VI - tap on cluster (x16-26) engine temp sensor
x9988-10 - SW - DME, EML, cluster,..etc. engine rpm
According to the ETK I need a new lock sensor 61 35 8 360 039 and an adapter wiring set 64 52 8 391 881. My guess is that the adapter wiring set goes between the car and the new lock sensor.
But as the compressor cost enought and I recently had the chance to pick some parts off a 93 750i I am now the proud owner of a 61 35 1 392 410 lock sensor with loose some wires.
So my plan is to splice the new plug into the wiring of the car, leave the temperature wires alone thus enabling me to use the newer lock sensor which doesnt need the compressor speed signal. If this doesn't work I'll tap into the cluster temp sensor and then it's 100% identical to the 92 upwards model years ans must work.
It seems to me in theory there are two other ways to bypass the old lock sensor:
1) Wire the input 12v from the compressor relay to the output to the compressor clutch thus bypassing the sensor
2) Also cut the x77-4 black wire so the lock sensor reads the compressor speed as 0 (as there is no speed sensor) and the rpm as zero (engine not running). This could fool the unit as it matches to two signals and disengages when the speed difference is 30% or more.
-->Both methods disable functioning of the sensor completely so use at own risk!
I found some postings on the net from Shogun and Hitmax which pointed me in the right direction. But as I collected all the part numbers and pinouts I though I'd share it just the same. -Johan-
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E32Fan:
Details are on pg 6450-22 & 23 at
http://www.e38.org/e32/e32_88_etm.pdf
I would open the A26 Lock Sensor Control Unit and solder a jumper wire across the Normally Open relay contacts. This will short X80 pin 3 to X77 pin 1 (shorting SW/RT/GE to SW/GR).
If there are no pulses from the reed relay in the compressor (because the new compressor has no reed relay) then A26 will de-energize its relay, but we won't care because the contacts are now shorted.
This will allow the compressor to run whenever K19 is energized and the pressure switches B7 and B8 are closed (just as in 735iL)
In later years, A26 was modified. The connector became X9968 which is not documented in the connector Views 8500. See 6450-22 at
http://www.e38.org/e32/e32_92_etm.pdf
I do not see any outputs from A26 that will bother EML, so I would not expect any problems from shorting the A26 relay. The SW/GR wire to EML is just the compressor run signal to inform EML that there is a compressor load.
Last edited by E32FAN; 04-07-2011