Actually, overfilling it causes the compressor to kick on and off quick, almost the same it does when you're refrigerant is getting low. Doesn't produce any cool air at all and burns you're compressor up. If you go buy one of those shitty things from like advance or something its really easy, but its still not done correctly. Just hook it up to you're line (the fitting only fits one anyway) and get the refridgerant. I'd let all you're previous shit out.(if you have any) Don't forget to buy the guage they have to see how much you have in there. Like i said, its a shitty way of doing it, but it will get the job done for a bit.