#1 - The illumination lighting has no connection to the A/C circuitry. From the wiring diagram the power comes from a junction C124 located in the RH drivers footwell. The junction gets its power from the dimmer reostat. Do your lights go up and down the same with the reostat?
#2 - That year Turbodiesel has no conection between tach function and A/C operation. I think a separate problem here.
#3 - The "Min" position turns off the heater valve no matter what the temp. "Max" turns it on totally. In between the valve is pulsed. The control is from a separate controller behind the glove box on the side of the evaporator housing. You will need a wiring diagram if you wish to check it.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician