I have a 96 cadi devill need to know how to restart my a/c has something to do with turning on and off the key

my a/c did work fine. it ran out of freeon ans so i felled it up and know the a/c on wont work and the a/c cluch wont turn on. i talk to a macanic and he said you have you to restart the a/c computer bye doing something with turning off and on the key many times and pressn reset. but im havein no luck. anything would help