With the climate control system I have you can set (for example) the type of car you have (R129 or W202), the type of engine that is installed (4/5/6-->12 cylinder, diesel or petrol) and the extension of the display readings (degrees Fahrenheit or Celsius).
I tried to change the motor type (holding the pre "96 instructions in my hand) and ended up with a system that only opened the ventilation ducts to the windscreen whatever my setting of air flow would be. I had the system reset by the dealer (YES, my personally installed "96 airco system can be serviced by the OEM mercedes service compu; the service compu doesn't even see that the airco was not original there).
I don't know how the settings got changed; but then again: I didn't even know what I was doing...(just pushing some switches, getting info, changing motortype...)
with a minor 600+k