My 2008 did the same thing 2 years ago and I added freon. Stopped hissing until this year and I added freon again and the hissing stopped again. I probably have a small leak as well. I used the AC Pro freon this year with the gauge and it was very easy to do myself.Artteran said:A/c is working now, however not very cool. About every 45 seconds I hear a hiss.