I pushed the little ball bearing (bleeder valve?) on the low side port to see if there is anything in the system and I hear a hissing sound, but I can't see anything. Is that freon that is coming out or what?
When discharged from a car's A/C system, freon is it's gaseous form. So yes, freon is coming out. It will normally be colorless.
Note that while very cold and under pressure it changes to a liquid form. During the liquid/gas transition (boiling point) of freon, bubbles can form and may appear to be white in color.
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