Nissan Repair: Nissan Sentra AC trouble, nissan sentra, clutch assembly

Question
I have a 2002 Nissan Sentra SE-R with about 86,000 mi. on it. Up until recently my AC was ice cold. But this evening I noticed that it was just blowing air. Also there was a breathy/hissing noise that I could hear from behind the center vents on the console. This noise was only heard when the AC was on and stopped when just set on fan. What might the issue be?
Thanks so much.

Answer
The a/c and heater is controlled by vacuum and electrical components. make sure the is no vacuum hoses disconnected behind the control panel which can make that hissing noise. Turn the a/c on and observe the compressor's clutch assembly, see if engages. If not, it could be a faulty low pressure switch or something in the electrical connection to it. That, of course if there is no leak that allowed the freon to escape from the system.