I am not familiar with Industrial 12a, whatever that is, but...

I would say that charging by sight glass is not the most accurate way to do things. Sure, the A/C may be blowing quite cold - I don't doubt it. But without knowing what pressures you are running, you may possibly be damaging or prematurely wearing your compressor. That sight glass was designed with R12 use in mind and is only to be used as an indicator when that particular refrigerant is in use.

I can tell you with a certainty that R134a runs at much higher pressures than R12, and if you put an equivalent charge into your system or charge to "clear" at the sight glass, you WILL damage or prematurely wear your compressor. I can charge up my converted system to approx. 250 to 275 cycling pressure on the high side, and the sight glass is all foamy. If I were to charge with more R134a until the sight glass was clear, that would put my pressure readings somewhere in the 350 to 400 or more range, if the pressure switch didn't kill the compressor first. Think of what kind of pressure that would generate at 3000 RPM! Evidently you feel comfortable not knowing the pressures your system is running, but be advised you may be setting that new compressor up for early failure.

I would suggest checking the temperature/pressure charge for that refrigerant before running a clear sight glass with it. Also, do a search on alternative refrigerants here, there has been plenty of discussion by the experts. Bottom line is that most if not all alternatives are actually blends of other refrigerants which leak out of the system at varying rates, resulting in inconsistent mixtures and the need to completely evacuate and recharge (rather than top-off). Also consider the possibility of contaminating recovery supply if the fittings are not properly changed on the system, per EPA 609 stipulation.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280