Bobby 5/20/2010first check if the a/c clutch is coming on, turn the a/c on then open the hood and the clutch should cycle on and off. if the clutch never kicks on then possibly the system has lost pressure due to a leak. if clutch is kicking on then could need a recharge or compressor, evap or condensor could be to blame
Bob R. 5/26/2010This could also be a failed blower door in the air ducts, especially with that hissing sound. If you have an electronic climate control, there's a couple little electric motore that operate the flappers that direct the airflow under the dash.
If you have manual A/C there may be a couple cables that could come loose. When was the last time you changed your cabin air filter? The access door for it is where the passenger's left foot would be under the center of the dash.
There are good diagrams at this link: