If the EC is 'stuck' on. . .
then I would agree that you can't acess the codes and start the compressor. You can verify that pretty easily, just look and see of the clutch is engaged. If not, the EC button must be fixed FIRST.
Under number "7", the refrigerant pressure, in BAR, can be seen; 13'1 = 13.1 bar (191.1 lbs). This is nornal pressure for a 'avearge' day, temp, etc.
Regards . . . . JimF
'94 S500 Cpe
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