a/c venting
 

I have a 2001 Diamante.

I was driving with the A/C on and bumped the button on the A/C panel that shifts the blowing from dash to defrost to floor, etc... and it shifted but made a funny vaccum sound, like when you have a shopvac and it picks up something that blocks the suction.

The a/c continues to blow cold air, and the fans are working but there is something blocking the center vents from allowing air flow and the air won't shift from dash to floor to defrost any more (although it sounds like it's trying to)... it's like there is a vacuum flap stuck closed or something blocking it, or the mechanism that shifts the airflow is stuck.

Any help on this would be much appreciated, or diagrams of the interior cooling/venting system ...please help, it was 112 today. thanks