I have a 2001 CLK 320. The side vents blow air, but not the middle. Can anyone tell me what the issue may be?

 

This is a duplicate post---as advised you have a flap issue---use your VAC control unit and preform the flap test---what are the results!!

 

...caused by a vacuum problem...

see this thread
success!!! got a connector for reservoir and voila, center vent blowing AC!!! If you have a center vent AC problem, start at the vent distribution box under glove compartment...I tested it with my mouth to see if suction....if none...trace back to air reservoir hidden behind wheel well (https://mbworld.org/forums/newreply....=714194)...see pics..etc...back to vacuum connection at engine....if any leaks along the way, the vents will all open and middle one stays closed....as soon as vacuum attached to distribution box, they should all operate normally.