I think Steve has it down pretty well. You do NOT want to see bubbles after start up. You can use a Gauge Set to introduce refrigerant and fine-tune, and Sea Frost will have instructions for this, a bit complicated but not overly. The Gauge Set will also tell you if you are over-charged. Once I get my system to where it needs to be for fill, I simply look for disappearing bubbles at start-up ... only after system hasn't been run for some time, I don't think you will see bubbles at start-up if the system is already cold ? I also shoot my cold plate with a digital thermometer, record those readings, and compare to previous readings. The Plate temp should drop rapidly in the first few minutes. If my Plate is say about 70 degrees before run, and has not been run for several days, it will drop to about 50 degrees after the first 5 minutes, then maybe 20 degrees after 10 mins, 0 to 10 degrees after 20 mins, and then below zero after that ... -10 to -15 is what I see. Cheers, John