What that reading means is that it was in the mid 80's when you checked the pressure. Doesn't tell how good the charge is, but it is definitley good enough that the compressor should have started turning. Time to check voltages to the compressor clutch coil. I do not recommend "converting".

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C