Any A/C repair manual or A/C theory of operation manual will have a chart showing ambient temp, relative humidity and normal high pressure readings for 134a. A/C operation and pressure readings are relatively the same regardless of what car its on. Most manuals say to have a fan blowing onto the condenser while recharging to simulate car in motion. If 310 is too high, then the pressure switches in line or at the rear of the compressor will either pop out or electrically disconnect the compressor. So, because you mention nothing regarding these things happening, I would say its working normally. The minor adjustments you did, I believe, corrected the different pressures related to R12 VS 134A effeciency.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.