A screw compressor system for a refrigeration circuit, comprising: - a screw compressor including a slide valve selectively actuatable between a first position and a second position to facilitate modulating a capacity of the screw compressor between fully-loaded and fully-unloaded; and - a controller communicably coupled to the slide valve, the controller configured to: - receive a chilled fluid temperature setpoint for a fluid in heat transfer communication with a refrigerant of the refrigeration circuit; - receive temperature data indicative of a chilled fluid temperature of the fluid; - determine a difference between the chilled fluid temperature and the chilled fluid temperature setpoint; - provide one of a load command and an unload command to the slide valve based on the difference between the chilled fluid temperature and the chilled fluid temperature setpoint characterised in that the controller is further configured to: - start a timer each time one of the load command and the unload command is provided to the slide valve, wherein the load command causes the timer to count toward a load time threshold indicating that the screw compressor is fully-loaded and the unload command causes the timer to count toward an unload time threshold indicating that the screw compressor is fully-unloaded; and - estimate a current position of the slide valve based on the timer relative to a corresponding one of the load time threshold and the unload time threshold, wherein the controller does not receive feedback from the screw compressor regarding the current position of the slide valve. - a screw compressor including a slide valve selectively actuatable between a first position and a second position to facilitate modulating a capacity of the screw compressor between fully-loaded and fully-unloaded; and - a controller communicably coupled to the slide valve, the controller configured to: - receive a chilled fluid temperature setpoint for a fluid in heat transfer communication with a refrigerant of the refrigeration circuit; - receive temperature data indicative of a chilled fluid temperature of the fluid; - determine a difference between the chilled fluid temperature and the chilled fluid temperature setpoint; - provide one of a load command and an unload command to the slide valve based on the difference between the chilled fluid temperature and the chilled fluid temperature setpoint characterised in that the controller is further configured to: - start a timer each time one of the load command and the unload command is provided to the slide valve, wherein the load command causes the timer to count toward a load time threshold indicating that the screw compressor is fully-loaded and the unload command causes the timer to count toward an unload time threshold indicating that the screw compressor is fully-unloaded; and - estimate a current position of the slide valve based on the timer relative to a corresponding one of the load time threshold and the unload time threshold, wherein the controller does not receive feedback from the screw compressor regarding the current position of the slide valve. - receive a chilled fluid temperature setpoint for a fluid in heat transfer communication with a refrigerant of the refrigeration circuit; - receive temperature data indicative of a chilled fluid temperature of the fluid; - determine a difference between the chilled fluid temperature and the chilled fluid temperature setpoint; - provide one of a load command and an unload command to the slide valve based on the difference between the chilled fluid temperature and the chilled fluid temperature setpoint characterised in that the controller is further configured to: - start a timer each time one of the load command and the unload command is provided to the slide valve, wherein the load command causes the timer to count toward a load time threshold indicating that the screw compressor is fully-loaded and the unload command causes the timer to count toward an unload time threshold indicating that the screw compressor is fully-unloaded; and - estimate a current position of the slide valve based on the timer relative to a corresponding one of the load time threshold and the unload time threshold, wherein the controller does not receive feedback from the screw compressor regarding the current position of the slide valve. - start a timer each time one of the load command and the unload command is provided to the slide valve, wherein the load command causes the timer to count toward a load time threshold indicating that the screw compressor is fully-loaded and the unload command causes the timer to count toward an unload time threshold indicating that the screw compressor is fully-unloaded; and - estimate a current position of the slide valve based on the timer relative to a corresponding one of the load time threshold and the unload time threshold,