Control Scheme for Refrig with Screw compressor

I am looking for help in finding control schemes for a refigeration unit driven by a screw compressor. This is an existing unit with compressor, VFD
fans on the condenser, and a product heat exchanger where the target temperature is taken at the process discharge.
The controllable components are the compressor's loading control (0 - 100%), the fan speed, and the water spray pump. The original supplier held the control proprietary and will not disclose the control scheme, they will only provide operating limits and start-up and shutdown sequences.
There are temp and pressure measurements around each piece of equipment but no flow controls.
Thanks for any help.
Richard
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