When the compressor runs at full capacity the liquid line sight glass is full and when the slide valve reduces compressor capacity the liquid line sight glass drops to half and even 1/4 full. I have seen flashing in the sight glass with reciprocating compressors running unloaded and clear up when fully loaded, so just wondering if this is normal with screw compressors or the system is low on refrigerant? The condenser water temp fluctuates it is not heated it is regulated with a water regulator actuated by system head pressure, 134a refrigerant which was running around 116, psi back pressure was 11 psi with 36 deg chilled fluid compressor running approx 50 percent capacity. Any input would be appreciated; thanks