I have a 97 SL 500 with a problem w/ the vent system not switching from defrost on the front windshield. I can't get it to blow air out of the other vents in the car.

I am guessing that there is something wrong w/ the vacuum controller that switches the vent direcion. Can anyone shed any light on this issue?

Will the dash have to be removed to get at the problem?

 

The vacuum elements for the malfunctioning vents are probably faulty. I think the diaphrams dry up and lose their ability to hold vacuum. The other solution (if your car has it) is the switchover valve block. On my '88 260E it is accessed by removing the glove box. The valve block is mounted on or near the heater box.

 

You could also have a code fault in your system. i had a new climate control unit installed, and it did not fuction properly. I tool it to another dealer and he hooked the car up to the computer. There were several fault codes in memory. When they erased the codes everything worked fine