They typically don't pull quite enough vacuum for A/C work. Operating on the Coanda effect, they might get 25-28", but that's not quite good enough. If you want to save some money, use an old dehumidifier compressor and solder a 1/4" flare fitting on the suction tube. I just made one, and It'll pull over 29", which is what you need (to vaporize all the water inside your car's system)

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.