There is a screw for adjustment. Access is through the center vents (they must be removed). The POT is on the top of the evap case. You will need better instructions than that to accomplish anything.
Do you have the chassis CD? They values change for the voltage. As I recall there are three different values depending upon the year. Testing needs to be done to evaluate this condition, unless you cheat.
We have made a resistor bridge that makes the right value for the output leg. (The potentiometer has power on one wire, ground on one wire and resulting output voltage on the third - to make the bridge two resistors are placed end to end with the output coming off the junction in between and the power and ground on the proper ends). In Florida its not a bad fix to just leave the bridge in. Those in colder climates will have to tell me why MB cared whether the mode door was all the way shut before allowing the A/C compressor to come on. I have placed this bridge in a number of old 190s for a cheap fix and can't see the difference in performance. Since the A/C has an on/off button it seems senseless to me.
If you want the resistances, I have them writen down at work.
Bosch Master, ASE Master, L1
33 years MB technician