96 C280 A/C Vent Problem
 

I have a 1996 C280 that stops blowing out of the center vents when you push on the accelerator. I had this problem about 2 years ago and traced the problem down to a cracked vacuum manifold in the engine compartment. Now its doing it again so I changed out the vacuum manifold but still did not fix the problem. I believe the storage tank may be cracked but don't know where its located. Any help would be greatly appreciated.

1995 C280
 

My 1995 C280 started doing this last Thursday. What vacuum manifold in the engine compartment cracked? Where is it located since I would like to check mine to see if that may be the cause of my problem.

It located right under the plastic cover at the right rear or the engine compartment. It should have five or six lines leading to it!!

A/C Vent problem
 

Any help out there guys?

Vacuum leak from fresh air element?? IF you switch the the EC button does the center vent stay ON? if so then the fresh air vent IS the problem & is a very common failure.

Ok I found that with the A/C on and the EC button depressed while driving...the air starts to blow out of the center vent more regular. With the EC button off the center vent will blow without the accelerator pedal depressed and will stop when you accelerate with the loss of engine vacuum!! I think I understand what you are saying but it seems to do the opposite because when you depress the EC button the vent starts to blow more regular and is not that dependent on engine vacuum!! Did I do the test correctly?

Any additional information on the cause of this, my 1998 C280 is doing the same thing. A/C switches over to defrost vents (from Center Vent) when I accelerate...only does this when outside air gets above 100 degrees ( I live in Phoenix Arizona)...pushing the EC button will make it switch back to full blowing from center vents...also does fine if I am not accelerating.

Yes, most likely one or both of the fresh air vacuum diaphrams are leaking.

You could try blocking off the 2 vacuum lines to that element OR remove the complete dash & replace it.