A/C Switch...possibly

Need some help. The other morning, it was a little chilly out, so I turned the heat up and put the A/C switch to defrost. After the weather warmed up, I turned it off. Today, it got a little warm, so I decided to run the A/C. When I moved the switch to "Max", I could hear a "hiss" under the dash, but felt no air coming out of the vents. The air is blowing cold (or whatever temp I set it at) through the defroster. No matter what temp, or what position I put the selector at (Max, Vent, Defrost, Heater), it's blowing through the defroster, with the ever present "hiss". How do I fix the "air flowing to the right place" problem? Thanks, James:smokin:

sounds like you have a broken vacuum line either on the temp selector control head or down at the door actuator. That is the hissing you are hearing...vacuum leak.