BY state laws of ALL U.S., you have to take it to a repair shop and have them vacuum what is left out first! Before they do this they can add dye to the system and locate the leak.
I Think I Have A Freon Leak In My 1998 Chevrolet S10. How Do I Fix It?
There is a guy on Ebay that sells a how to guide for $5.00. It worked for me and unbelievably simple in my case. I recommend you check it out and if you like it buy one. Just search "auto a/c repair". It should pop up......