Menu Content/Inhalt

Login Form






Lost Password?
AC Lock Sensor
Please note that year designations might not correspond properly depending on European or US manufacturing models.

The AC electronic system consists of several components.

  • The heater controls and IHKA control module
  • AC pressure switch on the drier bottle
  • Some models have a 108C coolant temperatur switch off device
  • The AC lock sensor module
  • AC compressor relay
  • Aux fan relays

The AC lock sensor monitors engine coolant temperature, compressor speed and engine speed. If all is well it allows the AC compressor to get 12 volts applied to enable the system.

In this example the control unit is from an V12 750 1989 model, part.no. 61.35.1.390.899(2).

DSC00731 DSC00730

Note! Only 750's have an AC lock sensor!

The unit is located on a bracket behind the left kick panel. Remove the kick panel to expose the two bolts that need to be loosened to hook the bracket off the chassis. The bracke also holds the Servotronic (if present) and AC compressor relay (1988 to 1991 models).

DSC00689 DSC00690

It's either got two green connectors or one bigger green connector. All in all there should be 9 pins if there's two connectors, and 10 pins if there's 1 connector. Not necessarily all are connected though.

1988 750's

Pin Wire color Description 
C1-1 

Black / Grey
Blue 

To DME's. Signals to increase idle speed when AC is running.
To AC compressor. 12 volts to enable compressor. 

C1-2 Green / Blue / Yellow Fuse 29 (12 volts when ignition in start or run) 
C1-3 Brown / Black Ground 
C1-4 Black DME pin 6. Engine speed signal from coil # 1 
C1-5 Brown / Violet Engine coolant temp.sensor (brown/white) 
C2-1 Black / Grey AC compressor speed signal (1 of 2) 
C2-2Blue / Brown AC compressor speed signal (2 of 2) 
C2-3 Black / Red / Yellow Low pressure switch* (source of 12 volts for compressor) 
C2-4Brown / Yellow Engine coolant temp.sensor 

 

 

 

 

 

 

 


*) The other end of the low pressure switch connects to the high pressure switch by a Black / Red wire. It then connects to the AC compressor relay via a Black / Red wire again. When the IHKA grounds pin A8 (Blue / Black wire) it enables the AC compressor relay which the energizes the Black / Red wire from fuse 29 (7.5A). The AC relay is connected to this fuse via two Green / Blue / Yellow wires. If the AC system pressure is correct, a 12 volt should be available at this pin when the AC mode is enable at the heater controls (ign. switch in position II or engine running).

1989 - 90 750's

Pin Wire color Description 
C1-1 

Black / Grey
Black / Grey

To DME's. Signals to increase idle speed when AC is running.
To AC compressor. 12 volts to enable compressor. 

C1-2 Green / Blue / Yellow Fuse 29 (12 volts when ignition in start or run) 
C1-3 Brown / Black Ground 
C1-4 Black DME pin 6. Engine speed signal from coil # 1 
C1-5 Brown / Violet Engine coolant temp.sensor (brown/white) 
C2-1 BlueAC compressor speed signal (1 of 2) 
C2-2Blue / Brown AC compressor speed signal (2 of 2) 
C2-3 Black / Red / Yellow Pressure switch* (source of 12 volts for compressor) 
C2-4Brown / Yellow Engine coolant temp.sensor 

 

 

 

 

 

 

 


*) The pressure switch is now an integrated 3-way switch in one instead of multiple switches. The other side of the pressure switch is connected to the AC compressor relay via a Black / Red wire. The pressure switch also has two other wires (Black / Grey / Yellow and Brown / Black) that controls the aux fan relay. The AC compressor relay is the source of the AC compressor 12 volt enable signal. It's hooked up to fuse 29 (7.5A) via two Green / Blue / Yellow wires. The IHKA pin A8 (Blue / Black) grounds the AC compressor relay thus enabling 12 volts to pass to the pressure switch, and to the lock sensor if the AC system pressure is correct (ign.switch in position II or engine running).

1991 - 1992 750's

Pin Wire color Description 

Blue 

AC compressor speed signal (1 of 2) 

Brown / Black Ground
Black / Red / YellowLow pressure switch* (source of 12 volts for compressor)  
Green / Blue / YellowFuse 29 (12 volts when ign. in pos. II or engine running)
Black / Grey

To AC compressor. 12 volts to enable compressor.
Is also connected to DME to increase idle speed.

Blue / Brown 

AC compressor speed signal (2 of 2) 

7Brown / Yellow Engine coolant temp.sensor 
N/C 
9Brown / Violet Engine coolant temp.sensor 
10Black DME and coil. Engine speed.

 

 

 

 

 

 

 

 

*) The pressure switch is now an integrated 3-way switch in one instead of multiple switches. The other side of the pressure switch is connected to the AC compressor relay via a Black / Red wire. The pressure switch also has two other wires (Black / Grey / Yellow and Brown / Black) that controls the aux fan relay. The AC compressor relay is the source of the AC compressor 12 volt enable signal. It's hooked up to fuse 29 (7.5A) via two Green / Blue / Yellow wires. The IHKA pin A8 (Blue / Black) grounds the AC compressor relay thus enabling 12 volts to pass to the pressure switch, and to the lock sensor if the AC system pressure is correct (ign.switch in position II or engine running).

1993 - 1994 750's

Pin Wire color Description 

N/C

 

Brown / Black Ground
Black / Red / YellowLow pressure switch* (source of 12 volts for compressor)  
Green / Blue / YellowFuse 29 (12 volts when ign. in pos. II or engine running)
Black / Grey

To AC compressor. 12 volts to enable compressor.
Is also connected to DME to increase idle speed.

N/C

 

7Brown / Yellow Engine coolant temp. sensor
N/C 
9Brown / Violet Engine coolant temp.sensor 
10Black DME and coil. Engine speed.

 

 

 

 

 

 

 

 

*) The pressure switch is now an integrated 3-way switch in one instead of multiple switches. The other side of the pressure switch is connected to the AC compressor relay via a Black / Red wire. The pressure switch also has two other wires (Black / Grey / Yellow and Brown / Black) that controls the aux fan relay. The AC compressor relay is the source of the AC compressor 12 volt enable signal. It's hooked up to fuse 29 (7.5A) via two Green / Blue / Yellow wires. The IHKA pin A8 (Blue / Black) grounds the AC compressor relay thus enabling 12 volts to pass to the pressure switch, and to the lock sensor if the AC system pressure is correct (ign.switch in position II or engine running).

Opening the unit by carefully pushing away the 4 clips on the side of the casing and pulling the top away from the bottom.

DSC00732

You can then remove the PCB (printed circuit board) from the bottom casing by carefully pushing out near the 4 tabs that hold the PCB in place, and pulling the PCB up and free from the bottom casing.

DSC00733

The PCB contains 3 IC's (integrated circuits), a relay, some diodes, transistors, capacitors and resistors.

DSC00734 DSC00735

Note! The following is specific to this exact part.no device. Yours may vary.

 

 
< Prev   Next >

What's happening

Haven't spent much time on the E32 or E34 lately, but today I got out in the garage and made some space and got up some shelfes which cleared precious floor and work space.
 
At the same time I did a quick tour of my E32 and noted down part numbers for various relays and modules. 
Read more...
 

Random Photo

IMG_1606

Date: 04/08/2013 Views: 1763 Owner: Amuso

Who's Online

We have 7 guests online