Well, i have fighted against a "yurk" chiller (loaded with R407C, yes i hate that refrigerant) that's trippin' on the freeze guard at one circuit, +3c (okay it'ts pure water on the cold side, a +12c/+8c system) Both circuits is a little underfilled, just about to flash in the sight glass.

However.... Suspicious about flow issues. Both circs is running with almost same values (+3c evap/+40c cond) but the circ thats trippin on freeze guard is running with deltaT 7c in/out on the water side, +3c subcool, +4c superheat, the other circ is +4c sub, +5 superheat and 5c deltaT in/out water side (yup it's plate heat exchangers), my service leader meaned that I would get a lower deltaT on the "problem circ" if I refilled it with refrigerant. But in my book... I would get a higher deltaT if its "Topped up" with missing ref., to get a lower dT, remove some ref. you get less effiency. I know that's its more factors that's making sense. But now. Just focusing on the ref. filling...