Sorry to but in. I work on chillers for industrial. Supplying cooled water for various machines. A sub cooling of 15oc should be acheavable with any system there or about and 5oc superheat give or take. If you are not acheiving this its the same route. Gas charge/condensor fault/evap fault/ tev fault/ and abnormal ambient range. Your gauges are your friend and a simple logical reason. Look for signs like liquid return to compressor(bottom iced up) or tev iced up, mass dt across evaporater, low diff across condenser etc