Air conditioning compressor doesn't engage

[BPH]

Now that the crank sensor is behind me...I hope, my 1999 C280 2.8 electronic climate control unit is permanently in the "EC" mode which can not be switched off as indicated by the red light. The air conditioning has been evacuated and recharged, fuses and wiring checked, and I have been told that the cc unit "ec" switch is deffective. Further, my independent shop says a replacement unit must be purchased from MB and programmed? Can anybody help me through this problem and the logic of the MB only programming thing for the climate control? Thanks!