Hi out there, I have a walk in freezer prior company kept charging system 2 times a year without finding leak. I got called out pumped system up with inhert gas found leak fixed it and installed new drier. two days later got called out unit not cooling sight glass yellow. pumed system down installed another new drier and evacuated system for 5 hours, system worked well for 2 weeks. got called out today sight glass green full of charge system works during the day but at night when temp goes down to 50 degrees unit pumps down. turn system off for 20 min and turn it back on system runs normally can anyone advise