vent problem, and its summer!!!!

[deathsquad24.0sx]

Okay i have a 91 240sx se with ac. I never really cared for the ac before because that was before it got to be 110+ and i really need to figure out why my vents wont operate correctly.

The problem is when i try to change the vent settings from defrosting the front windshield to blowing straight at my face and feet, there is a wierd noise like a very week motor trying to change the vents. And then all of a sudden a big click goes off and its still on defrost for the front windshield. please any advice for a hot and sweaty man would be great.