This is a 750 Ton machine, designed for 32°F Brine LWT, 56°F EWT, serving a manufacturing process. It is equipped with Solid State Starter, VGD, and HGB. Here's what happens:
The process drops off to nothing, EWT falls to the 32°, (LWT setpoint is 32°) the PRV closes, and the compressor enters stall conditions. The VGD moves to its full stall-prevention position, but as there is no refrigerant moving it doesn't seem to help. It will stay in stall condition forever. Discharge temp rises to around 167°F! The VGD counter is already infinite at 999,999 and the other window (I can't remember what it was called) is at 74 days. This machine is very new and it's possible it has only been running for 74 days. Once in a while the process picks up and the machine comes out of stall. Also, if I manually open the HGB it comes out of stall.
Why doesn't the HGB open by itself? Or why doesn't the machine pull down to 29° LWT and shut down? This is a new plant so they are having production issues and that is why there's often no load.