I decided to experiment with a little more refrigerant since I have another can in my toolbox.
Sorry I don't have more concrete data. I don't have a scale to use and I can't find my pocket thermometer.
I added a "shot" that was just enough to raise the low side to 30 and the high side is steady at 200.
It feels colder for sure. The hose end that attaches to the evaporator is colder and sweating. I can see the needle on the low side gauge sweeping up and down a few PSI. The expansion is metering the flow.
I'm going to leave it here. If I had to guess at the charge volume, I'd say 14-16 oz. The second 12 oz can still feels pretty full.
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