You guys will have to excuse me, as I have less than 3 years and only one year in commercial. I also have little experience in refrigeration but occasionally have to do it.
I have seen on several occasions a sight glass on a rack that I am charging having bubbles in it, though dry, but the subcool is correct. I would wait aroung for twenty minutes to a half hour thinking they would go away. They didn't. I would add a little 22 and the bubbles would persist, though my subcooling would go up 1 degree. I would verify my split in the walk-in and all was good, so I left it and no problems or call backs.
I would never have thought about it again, but I have found this website and have been studying these forums and it raised the question. I do not have specific data on a specific job, as this happened to me twice last year at different locations and only now am I curious about it.
Both days would have been around 110 degrees in the desert, maybe 125 on the roof, with low relative humidity, and I was working on walk-in refrigerators. I am just asking if this is common or if there was an underlying problem that I was unaware of. If I didn't provide enough info for the real pros I appologize.