Thanks, UK. Also, I guess it sucks refrigerant from a can since even though there may be 30psi on a guage, the can itself has way more, I guess about 100psi or so?? Then, the HIGHER psi in the an overcomes a psi much lower in the suction line(?) Does that shed light on this UK?
well, "suction" line is called suction cuz it's connected to suction port on compressor; it is relatively
low pressure line, as compared to the high side of a/c system.
freon mix is sucked from can by compressor. you have a specifically designed system to maintain fluids flow in one direction. when you have can connected, freon is being sucked out of it by suction action from compressor. simple proof is, if compressor does not work, can will not release into system. should you have had a much higher pressure in a can, it would have released by itself. it does not, and on some cars, one has to trip compressor into action for freon to flow into the system during refill.
indeed, just like fabr said - air flows into combustion chambers, and quite violently, due to suction created by pistons.