HI I wonder if anyone could help. I have a Hitachi 4001SCH Screw compressor on a 1993 Hitachi Chiller, running on R22. On start up the compressor pulls 16 amps and slowly ramps up to 75 amps full load over a period of 30 minutes or so. This is a old chiller and works on a primitive loading and unloading system. However test have proved that there is no power to the unloading solenoids, there doesn’t feel that the solenoids are letting by, and the suction pressure is 5 bar, discharge 15 bar at low amps but then at full load amps of 75 amps drops to 12 bar with a SP of 4 bar. on low amps there is limited cooling, however once full load has been reach full cooling. But I can’t see where the compressor is losing. Other things I have tried and tested, Compressor windings, Contactors, and electrical circuits. Liquid by pass appears to be intact and not letting by. The compressor is a rebuild, and was replaced by a and other in 2008. Any suggestions would be appreciated.