the vibration is due to the idle being low. only thing you can really do about that is adjust your idle speed on the throttle body.

it sounds like your compressor is turning on, because when you press the button the compressor kicks in and robs power from the engine, thus the decrease in idle speed and cause of the vibration. as for the 25 lbs of freon, i don't know about that, but you may want to get one of those $ a/c checks at a mechanic. my compressor was kicking in, but the bearings were shot so it got locked up and wouldn't cool the car. it produced a horrible smell, turned my compressor a reddish color and threw metal shavings on everything.