I am new member and question is: On 95 C220 the AC blows cold ok but does not blow thru center vents, only blows thru side vents on dash. Repair center replaced AC switch, but this didn't solve problem. When set on AUTO, the air speed changes frequently and only blows out of side vents - does not blow at all from center vents. This is normal for heater air (I think), but air conditioner should blow from center vents also. Repair center owner said he would take back switch, but wasn't sure what the problem is. Anyone have any ideas on this?

Thanks,
Jerry

 

your vents are vacuum controlled, check the vacuum cell behind the cubby
that controls the centre vent flap with a vacuum gauge, it probably leaks.
replace it and you will restore your air thru your centre vents.

russell

 

I have the same problem with my 99 S320. Is this the same area I need to check on mine? Let me know

 

s class works on the same principle also vacuum controlled, you just have the added option
of controlling what air (hot or cold) thru your centre vents with the red and green button
the PSE pump under the rear seat supplies vacuum to all the vacuum cells for the A\C system.

 

Russell, I located the pump under the rear seat. How do you check it? Can you hear air leaking or do you use a gauge. If I had to replace it, how much would cost?

 

you must check it with a vacuum gauge. if you have access to star of a HHT you
could scan the PSE system and you would normally get a Fault "air demand too high"
but you must physically check with a vac gauge to pinpoint the leak.

Call you local MB dealer for a price onceyou know what part you need.

 

Russell, what is the procedure for checking. A mechanic friend let me borrow his vacuum gauge. I just need to know how to use in regards to checking for leaks.

 

I normally start checking for leaks, where all the vacuum pipes split, there is a valve block behind the cubby, i remove each pipe one at a time connect a vac gauge and draw a vacuum up to about 800mbar, and see if it holds vacuum. if the gauge falls just follow the pipe to the relevant cell and replace it. all the pipes are color coded so it's not too difficult.

 

Russell, you reallly got me confused. First of all what is a cubby and what is a cell? And where are the cells located at? As you can see I'm pretty new at repairing Benz. I guess I need to understand the lingo?

 

Can anyone help me out, I checked the pump with a vacuum guage and the there wasn't any leaking lines. I did notice that the pump is not pumping. Does it have a fuse I need to check, if so where is it located.