If you have a dark garage and a xeon light (ultraviolet prefered will glasses) then this will work. first go to an automotive parts store or dealership and ask for air conditioning ultraviolet dye.

put it in your air conditioning

pop your hood and kill all the lights

start your car run the a/c

using the xeon or ultraviolet light shine it into your engine bay around all the a/c lines and fittings.

you will see where the leak is because there will be a bright colored dye coming out.

hope this helps