Control Unit Not Responding? Troubleshooting Guide.

Hello first of all .

Okay, now for my problem: The control unit for my automatic climate control system is no longer responding.
"When I turn the ignition on and off, the display always shows 'OFF'. When I then press 'Auto', the air conditioning works perfectly, but as soon as I turn the ignition on and off again, everything goes back to 'OFF'."
My friend also tried to access the control unit and read data from it, but without success. He uses his laptop to access other components in a similar way.
I'm really stuck and don't know what to do anymore. Is there a keyboard shortcut or something similar to reset the device? I've also disconnected the battery several times.
Best regards, Carsten!!!

VW Sharan, year of manufacture 1999, 1.9 TDI.

Cross-reference...

http://www.sgaf.de/viewtopic.php?t=38512A proper diagnostic tool is usually able to determine the status of the diagnostic lines (short circuit or open circuit). Furthermore, it is not clear what type of diagnostic tool you are using, nor whether you are able to access any control unit at all.

I can't say whether a proper diagnostic device can do that, but Bosch and two other VW dealerships told me to just replace it.
And I haven't made any progress with the SGAF either; that thread was started by me!