Charging mystery unit

Been asked to repair a hydraulic fluid cooler. Three phase 200 volt compressor, R-22 unit. Looks like about same size as about 12,000 BTU per hour residential compressor. No name plate was found, with charge weight. The evaporator came apart, and I made some tubing to compensate for that.
How to meter in the correct charge? Suction pressure? Superheat? Amp draw?
Christopher A. Young Learn more about Jesus .
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