What is the function of LOCK-SENSOR

When I was trying to fix my servotronic in my 850 -91 I found another riddle!
First of all I just want to say that I consider my car to be very little tampered with. But in my hunt for the servotronic failure I discovered proof that somebody had been there before me, in this case behind the kickpanel (speaker cover) and behind and under the speaker at the driversfeet (you have to remove the speaker to get to it).

When I finally located the plastic bracket that is supposed to hold the servotronic controlbox I discovered two things:

First: The servotronic box is missing and the contacts is just hanging loose (two yellow round ones). For now I'll just connect them together, that will give max power assist independent of speed (I've tried this in my 735-91 and it works!.

Second: On the same bracket there are another controlbox, It was disconnected!!! It's labeled LOCK-SENSOR and is aprox. big as an cigarette pack. You can find it in the ETK diagram 61_0809. My box has part no: 6135 139 2 410. In the ETK it can also have no: 6135 836 0 039 it's called CONTROL UNIT LOCK SENSOR.
What does it control??? Except for my servotronic everything works or does it!!!???

As you understand I'm very interested in getting an explanation....

Please help I can't sleep good any more...

I'm very grateful for any theories.

/Björn

My guess is....

The Lock Sensor Control Module (A26) senses the following:

• A/C compressor RPM via integrated Hall-effect sensor
• Engine crankshaft RPM via TD signal from DME cyls 1-6
• Engine coolant temperature via NTC sensor

If the engine RPM is greater than 500 RPM, and the A/C compressor RPM is less than 30% of engine RPM, it's assumed the A/C compressor is seized, and this module releases the A/C clutch by interrupting the clutch control signal from the IHKA. Cycling the ignition switch to OFF will reset the module.

It also monitors engine temperature, and if it exceeds 240F (117C), cycles the A/C compressor intermittently for 20 seconds on/off to reduce engine load. It shuts the A/C compressor off complete if engine temperature exceeds 250F (120C).

If this module is disconnected, the A/C compressor should not engage. Does your A/C compressor work?

Mark

Thank you Mark for your specific answer I'm impressed!

I tried to find out the funktion myself but with poor result (I have nearly all the electrical schematics on paper but I couldn't make out the funktion...)
Of course you are right when it comes to if my AC works, it don't.
I was informed about that from the seller but not why it didn't work.
It has been converted to the new coolant but the system leaks (it looses preassure over night). I just removed the compressor for having it rebuilt.
As you understand it was VERY interesting to find out about this controlbox before I tried to start the AC again.
Up here in the north we only need it for about max 40 days a year but it is the principle that everything should work that is my goal.

Perhaps you can aswear another question:
What is the best way to remowe the main coolant pipe between the cylinderheads (for changing the O-rings).

Thanks again

/Björn

Bjorn,

I' assuming you mean the long water return pipe running the length of the engine "V" back to the water pump?

For those of you not familiar with what what I'm guessing Bjorn is fixing, here's some background pictures:

(no picture)

Water is returned to the pump via these two pipes. The smaller one returns water from the interior heater core. The larger pipe on the right returns the hot water from the rear of both cylinder heads via a manifold. The pipe leaks here:

(no picture)

So, to fix the leak, the repair manual states:

1.Remove left and right intake manifolds (ouch!)

2.Remove water pump (ouch!)

3.Pull larger of two pipes forward from rear water manifold

4.Replace O-ring in rear water manifold

5.Lubricate O-ring with Vaseline/glycerine/Gummiphlege

6.Reinsert larger of two pipes with twisting motion

7.Reinstall water pump with new pipe O-rings (there are two) at back of water pump

8.Reinstall intake manifolds

I'm assuming you've removed the intake manifolds already and just need to replace the leaking O-ring at the back of the "V" where the larger coolant pipe meets with the rear water manifold. Otherwise, you're facing a lot of work. You might be able replace the O-ring without removing the intake manifolds if you have small hands.

Also, Bjorn, now would be a good time to replace the cylinder block water jacket cover gasket located beneath these two pipes. There's an improved gasket to eliminate the leaks you'll see there.

Sorry if I'm boring you with the pictures. Just figured some folks would like to see the inner workings of the cooling system.

Mark

Yes, you got it right!

I've removed the manifolds so there is no return...
I was hoping that I didn't have to remove the waterpump. I thought it might be possible to remove the rear water manifold instead (it seems impossible to reach its bolts, very tight).

Thanks for the tip about the "cylinder block water jacket cover gasket" I'll follow your recomendations (of course) and replace it to.

Your pics are anything but boring!!! It's so very nice of you to take the time to post them with your instructions/advice. Pics always makes it easier to understand and prevents a lot of missunderstanding.

Thanks again.

/Björn