Out of the blue, my middle 2 vents have stopped giving air even tho the sliding lever is on open. Air is only coming out on the dash where the front window is . I do understand that when u change the dial to heat, the hot air is automaticaly sent to the dash vent and to the feet. but when switched back to cold it should be back to the middles. the side vents are giving air , just not the middle.

the only thing that has happned with the car, is i had it detailed a month ago and i didnt drive it for a few weeks.

ive tried running the air on econ, normal and bi level but not give air in the middle 2 vents.

please help
thanks

 

I am having the same problem on my 86 300SDL. I only get heat or cold from the windshield vents and side vents, it won't change no matter what buttons I press! So frustrating when my feet are frozen here in Seattle!!

 

there is a vacuum solenoid that is no longer working, it is the one that opens the air flap to the center vents. The part is not expensive but it is kind of a pain to change, if you do a search on benzworld.org you will find a few how to's.