Dash Removal Guide, Center Air Vent Solution, How to find Vacuum Leak, 148 pics

[zadefaraj]

With this post, I will detail how I found my vacuum leak, and how I removed my dashboard and all the components to access and correct it. Please read it in full, and note that this is only for reference and may possibly contain errors, missing steps, and, or information specific to my 1995 C280. In other words, I don’t want to be held responsible.

http://www.corpfr.com/c280/Dashboard.htm

It's about 13 pages of text, and over 140 pictures, and way too large to fit on one forum. Took me a while to write up so I hope this helps someone.


Zade Faraj

[renerodz]

Hey,

Thanks much! I have the problem too.

Rene

[alphanumeric]

I might have this same problem.. when any AIR is blowing through my system.. I cant select which vent the air comes out of.. it comes out of every vent no matter what I select on the climat control knob.

I thought it was from installing my own head unit... and hopefully wont require the whole dashboard to be removed...

[zadefaraj]

Before removing the dash, I would have a good look at
1. the vacuum distributor block in the engine compartment, and
2. vacuum test all the lines on the vacuum control unit attatched to the fan motor box, behind the glovebox. The pics and info should guide you there :)


Zade

[zadefaraj]

Btw, you can also vacuum test all the lines on the vacuum distributor block in the engine compartment. The only one I know that leads to the vents is the green one, but I'm not sure if it will give you any info if it does or does not hold pressure. The only way to accurately tell if any of the lines in your vent system aren't holding vacuum is to test them individually.

Zade

[htfan1]

Thank you very much zadefaraj!

We appreciate you sharing all of your hard earned information.

I'm just another member of the "annoying vacuum pump noise and busted center vent" club.

[zadefaraj]

No problem! I hope everyone finds the info useful. Beleive me, those center vents are a life saver now that summer has started in Texas. You know, if you test the vacuum lines behind the dash, and find out that the one affected is number 106, then you shouldn't have to remove the dash.

http://www.corpfr.com/c280/CIMG1722.JPG

I replaced number 104 and number 32, where 104 was the one that controlled the center vents. You might be able to reach it without removing the dash via the guage cluster cavity, but im not 100% sure.

Good luck and i'm here if anyone needs more info.

[Abuimad]

i got the same problem, thanks a loot for that post

[nick_nolastname]

Whoever you are, I want to offer you my sincere thanks for going through all the trouble to document that.

Volunteer tech support in forums is often taken advantage of without so much as even a thank you. I wanted to make sure this time is different. Your work will be a help to countless people across the world because it seems most of these cars are afflicted with this same problem.

I've downloaded your instructions and pictures, and it helped me find the problem with my wife's car. Im on the way down to MB in a few minutes to get the part. Your instrument cluster and radio removal instructions will help me replace the burnt out bulbs as well.

Do you have a Pay Pal account? I'll buy you a couple of beers.

Thanks buddy. Thank YOU!

[zadefaraj]

Thanks so much for taking the time to be so kind, you are more than welcome. I hope you didn't run into any problems, and if you do, please feel free to drop me a line at zadeatuh@hotmail.com

Btw, Thanks for the drink offer, and if you ever happen to make it down to Houston, maybe i'll take you up on that.

Take care and let me know how it turns out; Are you fixing a vacuum leak?

[sultanC36]

thank you zadefaraj

for the write up it is a huge help

[nick_nolastname]

The vacuum distribution block under the hood was cracked, causing the high rev shift from second when cold as I read about, and also the center vent cycling on and off when you accelerate and let off the gas thereby changing the engine vacuum. I replaced it for $24 or something close to it. It cracked at the little ball bearing just like everyone elses.

The right center vent bellows was leaking, so I plugged it up.

That passed the remaining vacuum to the left one, which works.

I will accept 1/2 a center vent rather than pull the dash out.

The only remaining problem is the recirc vent, if activated, will cause the trunk vacuum pump to cycle. I told the wife to just not use that, she never does anyway.

The trunk pump will also cycle if she puts the temp setting on LO instead of a number, or if the climate control is turned off entirely. I am guessing that this is due to the recirc closing for maximum cooling or just sealing the car up with the climate control is off.

All in all, what a quirky and stupid idea, must have been all that strong German beer they drink over there.

I would not consider the purchase of another Mercedes after owning this one. They have lost me as a customer for life. But the wife loves it so I am stuck with it as my German kit car for a while at least. You wouldnt believe all the other things that have gone wrong with this car.... or maybe you would. If I hadnt done almost all the work myself we would probably be out another 4-5K for repairs.

To reciprocate in sharing knowledge, I've replaced the water pump. If you need a little coaching with that send me a PM through this forum so I will get an email about it. I dont check this forum except when her car breaks. ( so about once a month from now on LOL ) I've replaced a lot of other crap too but based on your online guide you wont need any assistance with those things, you have the skills to figure it out yourself. The water pump can be a little tricky, but once you see how its done it's almost elegant the way it goes together.


Good luck to all.

[1998K]

Dear Nick,

I really thank you for all your contribution on our forum.

thanks

Marco:)

[htfan1]

Originally posted by nick_nolastname


The right center vent bellows was leaking, so I plugged it up.

That passed the remaining vacuum to the left one, which works.

I will accept 1/2 a center vent rather than pull the dash out.



I have some questions and would appreciate the help.

1) Were you able to get to both center vent bellows without pulling off the dash? If so, how did you access them?

2) What were the ref. numbers for the center vent bellows on the diagram provided by zadefaraj?

Diagram: http://www.corpfr.com/c280/CIMG1722.JPG

I'm ready to dive in, would just like a better idea of where...

[zadefaraj]

htfan1,

The center vent bellow that I replaced was Ref. No. 104. It is to the left of the center vents and COULD possibly be reached with the gauge cluster out of the way or from below the foot well. I'm not sure if its entirely possible because I haven't checked, but if you are in the process of taking out the dashboard, try checking it out. Actually, from what I recall, it might be possible to reach it from the drivers side footwell, but its an awful tight squeeze. I'll have a look tomorrow and let you know if it can be done.

Take care, good luck, and let me know if you need any more help.

;)

zade

[htfan1]

Originally posted by zadefaraj !!
htfan1,

The center vent bellow that I replaced was Ref. No. 104. It is to the left of the center vents and COULD possibly be reached with the gauge cluster out of the way or from below the foot well. I'm not sure if its entirely possible because I haven't checked, but if you are in the process of taking out the dashboard, try checking it out. Actually, from what I recall, it might be possible to reach it from the drivers side footwell, but its an awful tight squeeze. I'll have a look tomorrow and let you know if it can be done.

Take care, good luck, and let me know if you need any more help.

;)

zade

Thank you again zadefaraj

I've spent the last hour listening for leaks in my dash.

There is a loud hissing noise coming from what I beleive is a bellow directly behind the center of the passenger side mini-glove compartment. I've removed the bottom cover panel on the passenger side and the glove compartment velvet insert.

Could this be it?!?!!? The hissing noise seems to match the vacuum pump pulses. When I place my hand next to it I can feel a subtle pulse of air.

I may be able to get to it without removing the dash. I can't really tell which number it is on the diagram you provided (could be #352).

What do you think? Could this bellow (?) be causing my center vent issue?

[zadefaraj]

I replaced my number 352 and that was the hardest one to reach. Its a pain and most likely requires you remove the entire dash. I was not able to reach it without removing it, and even with it out, I still hard a hard time getting a finger on it. The loud hissing noise you may hear could be coming from that vacuum diaphragm block in the engine compartment. The best way to test for a leak is to purchase a small vacuum pump from your local auto parts store and test the lines shown in the pics. Thats a sure fire way to figure out which line is leaking, and trace it to the source. Listening for the leak didnt help me very much. It was so hard to hear with all the things going on in the car, its almost impossible. I'm also not sure why you would feel a pulse of air, if anything, it should lightly cause suction on your finger. Provide more info and details and I will be glad to help. I've got to rest now though, got exams.. ughh.

zade

[zadefaraj]

Just wanted to add that number 352 is behind the passenger airbag, just behind the start of the windshield against the firewall. Its very deep, and if i recall correctly, virtually impossible to reach without removing the dash. keep me posted!

[htfan1]

Originally posted by zadefaraj
Just wanted to add that number 352 is behind the passenger airbag, just behind the start of the windshield against the firewall. Its very deep, and if i recall correctly, virtually impossible to reach without removing the dash. keep me posted!

Yes, the leak noise seems to be coming from 352. Too bad is so hard to reach. I'll stop and get a vacuum tester to narrow down the actual problem.

For now, I've disconnected the green power connector from the vent control block. This has STOPPED the vacuum leak "and the pump "whrring" noise", but I can no longer control my vents. The air comes out to top and sides only (still better than WHRRING).

I'll try running this way temporarily, because it's wonderful driving without the dreaded vacuum pump noise!

[htfan1]

Does anyone have a list of the connections between bellow number on the diagram http://www.corpfr.com/c280/CIMG1722.JPG and the #'s on the vacuum/vent control block http://www.corpfr.com/c280/P1010184.jpg ?

For example, bellow number 104 connects to #6 on the vacuum/vent control block. (just an example, I don't know which one it really is.)

[nick_nolastname]

Originally posted by htfan1
I have some questions and would appreciate the help.

1) Were you able to get to both center vent bellows without pulling off the dash? If so, how did you access them?

2) What were the ref. numbers for the center vent bellows on the diagram provided by zadefaraj?

Diagram: http://www.corpfr.com/c280/CIMG1722.JPG

I'm ready to dive in, would just like a better idea of where...

What I meant by "plugging them up" is from the passenger side lower panel access to the dash I took those individual lines going to the bellows and sealed them. Apparently the two center dash vents share vacuun, so if one leaks the other will fail to function. I blocked off the faulty one with silicon sealer, leaving the other operational. Keep in mind I am strictly a DIY'er so you can take anything I say for what its worth. Good luck.

[zadefaraj]

By disconnecting the power to that distribution block, you have pretty much stopped the vacuum from being redistributed when you change vent positions. I'm quite suprised you are actually able to physcially hear the leak because as I said before, mine was so small, it was undetectable.

Also, I'm sorry, I dont have a diagram that shows where all those lines go. I was going to make one, but I'm not sure what happened. I think the vacuum pump will be very helpful in determining which bellow is afflicted, and could save you from potentially having to remove the dash. If it is number 352, then I'm afraid their is little hope.

If you ask me, I think the repair was worth the time and money. I spent a lot less than paying at a dealer, I learned a lot more about my car, and the A/C works absolutely perfect. Now i just wish the the rest of the car was the same.

I think one of the main reasons these fail is because of their location and prolonged sensitivity to heat and other such extreme conditions. These days, I try to always park my car indoors or under some sort of shade; protecting my dash and all the delicate items behind it.

If you do decide to take out the dash, theirs a lot of stuff to keep together, so organization is the key. Also, try and replace and small cushions that may be in place because they help prevent creaking when you drive over unstable roads.

Feel free to ask more questions!


Zade

[zadefaraj]

you could also try checking with the dealer to see if they know which bellow each line connects to. Worth a try :)

[htfan1]

Originally posted by zadefaraj
you could also try checking with the dealer to see if they know which bellow each line connects to. Worth a try :)

Thank you! I appreciate your input.

As I go through this, I'll document what I find and add to the knowledgebase here.

One more small question: What is the proper way to remove the vacuum connections from the vacuum/vent control module?

Do you have to remove the entire top with all line attached? Or just pull out each one...

[zadefaraj]

You have to pull the entire line assembly off. You might want to draw out which one goes where (color with hole number) because it will get confusing if you dont have the factory diagram. The pics show how to release the locking mechanism:

http://www.corpfr.com/c280/P1010185.jpg
http://www.corpfr.com/c280/P1010188.jpg
http://www.corpfr.com/c280/P1010189.jpg


It almost feels like you are peeling it off from one side to the other. Its quite flexibile if you ask me, but be on the safe side.
Once you have them out like in this last pic, you can simply push them upwards and pop them out to test each line individually if you'd like. Keep in mind: the far right one should be the one that supplies the vaccum. Test them all and let me know what happens. :)

http://www.corpfr.com/c280/P1010193.jpg

zade

[htfan1]

Originally posted by zadefaraj
Once you have them out like in this last pic, you can simply push them upwards and pop them out to test each line individually if you'd like. Keep in mind: the far right one should be the one that supplies the vaccum. Test them all and let me know what happens. :)

http://www.corpfr.com/c280/P1010193.jpg

zade

The verdict is in:

Three different leaks! Yes, not 1 or 2, but 3. Line #8, #4 & #2 are all bad. #2 & #4 are very bad! BTW, The center vents seem to be controlled by #4.

How difficult is it to remove and replace the bellows? What is the proper procedure? (I think I can get to some of them without removing the dash.)

[zadefaraj]

Awesome! Well.. not the problem, but at least you've narrowed it down.

Let's see.. the way I replaced the bellows was by first taking them off of whatever they are attatched to via a clip. The clip should be on the backside, and i beleive the bellows slide UP to come out. Then, once the bellow was detatched, I proceeded to remove the metal arm that connects it to the flap (from the bellow side). I did this by pretty much peeling it off like distribution block thing. ie: rotating the billow to kind of 'pop' it off the lever. 'like a bottle opener'.

Now with the bellow just connected to the vacuum line, if I recall correctly, i stuck mini screwdrivers or something small around the opening to pry the locking mechanism open and get the vacuum line out. I beleive the lines we're held in place this way.

Replacing it is easier, and you should be able to follow the same procedure in reverse order.

If it takes some time, dont get too frustrated, even if you can see them, they are still quite difficult to work with.

Also, if you find that number 352 is one that is bad, and number 154 (the center vent controller), try replacing number 154 first. If you can reach it without removing the dash, maybe you might be interested in just sealing the number 352 line. If you get the cenver vent bellow replaced, try covering the number 352 line with your finger from the distribution block end and see what happens when you change the vent positions.

Also, for some reason, and this might make your task easier, sometimes 2 lines found at the distribution block connect to only 1 billow. Best way to find out is to write down the colors of the lines that are bad, and try and trace them. Some are easier to find than others, but like I said, number 352 is just stupid. If you can reach, play around the the metal arms to see what they control, but be careful, their edges are like razors!

keep me posted ;)

zade

[htfan1]

I appreciate your encouagement.

I'm going to try a workaround first by just plugging the 3 bad lines on the vent vacuum module. I'll find some rubber cap that will do the job and not damage the unit.

If the vent control is then somewhat functional with 5 of the 8 working, I'll make the decision to replace bellows or not.

By the way, where did you purchase your replacement bellows?

I'll continue and keep you updated.

Jeff

[zadefaraj]

Sounds good! I got mine from one the local dealerships in Houston; Star Motor Cars. I find most of their prices reasonably fair, and sometimes 70% cheaper than the other Mercedes dealership in town. I think I purchased mine for about $60~80 each.

http://www.starmotorcars.mercedescenter.com/mbcenter/b/services/serviceparts.jhtml

Good luck!

zade

[htfan1]

The test is going GREAT so far! I have plugged line #2, #4 & #8. The funny thing is the vents still seem to be "mostly" working properly.

I purchased some small plastic screw tip protectors from a local harware store. (The type normally used to cover the sharp ends of screws protruding through material.) These screw protectors fit PERFECTLY over the vacuum line ports on the vent/vacuum control module.

NO more vacuum whrring noise! I still have required control over critical vents. The only issue is the center vent will stop working from time to time ONLY when A/C is on. If I'm not using A/C, the center vent works fine.

I'm still in test mode, but this is a much, much better situation then before!!!! I'll keep you updated.

[crit1]

The link to the dashboard removal does not work for me. Can someone repost a functional link please? Thanks.

[crit1]

Never mind. I found it. Thanks a bunch.

[alphanumeric]

crap the link doesn't work? how did you find it? I really need to get around to doing this to my car someday lol

[zadefaraj]

http://www.zadefaraj.com/dashboard.htm

[nick_nolastname]

Once again thanks for posting such a detailed guide.

I realize this thread has not been touched in quite some time, but I'll bet people view it quite a bit.

For people that have a problem with just the center vents, like I do, I'd like to share what I did to solve the problem.

1) Remove the passenger side footwell cover on the bottom of the dash. You have to turn the phillips on the black vent 1/4 turn CCW and pull that out, then remove the three phillips holding the cover in place. Now remove it.

2) You will see two vacuum modules underneath, that have metal levers going up into the dashboard. These control the center vents. If yours are leaking and the pump keeps running, disconnect the vacuum lines to them and block them off so it wont leak any more.

3) Now using a long tool like a 12" pair of hemostats, reach up in there and pull the metal rods off the plastic cranks that control the vent doors. Now, just turn the vents to open and they will stay that way! If you ever need to turn them off, use the wheel on the front of the vent like you normally would. Voila! Problem solved. Why would you want to put another vacuum module in anyway if they are such peices of crap? Its a bad system. Thats the way it is.

Also, another thing I discovered today; my blower had a squeaky noise/clicking noise that was most noticable at low speeds. I figured some pine needles or something had gotten stuck in there, but I was wrong. The motor sits on two rubber cushion things that had settled a bit, and the rotor part was rubbing ever so slightly against the base of the blower housing. I took out the two screws that hold the moter into its housing, dremalled off the washers, and inserted two new washers ABOVE the rubber mounts, to increase the rotor to housing clearance by 1mm. Now its as quiet as the day it was made.

Good luck.

[OzC36]

Good write-up...thanks Nick!

[OCKlasse]

Can't wait to try this thank you!

[OCKlasse]

2) You will see two vacuum modules underneath, that have metal levers going up into the dashboard. These control the center vents. If yours are leaking and the pump keeps running, disconnect the vacuum lines to them and block them off so it wont leak any more.

Hey, so what did you do to "block off" the vacuum lines?

[nick_nolastname]

Silicon sealer.

I dabbed a bit on, then let it dry before starting the car back up. I didnt want it to get sucked up the line while still soft.

If you care about not having to pick it all off to use the lines again someday you will probably want to choose another option. This is my permanent repair so I dont care about that. Perhaps there is a joining piece you could get from MB that would allow you to connect the two vent lines together.

[OCKlasse]

Originally posted by nick_nolastname
Silicon sealer.

I dabbed a bit on, then let it dry before starting the car back up. I didnt want it to get sucked up the line while still soft.

If you care about not having to pick it all off to use the lines again someday you will probably want to choose another option. This is my permanent repair so I dont care about that. Perhaps there is a joining piece you could get from MB that would allow you to connect the two vent lines together.

Any way you'd be bored enough one day to take a pic in there? :o :D

[nick_nolastname]

I would... does this site host pictures? I dont see how to do it.

I really feel for people who own these cars and I do want to help.
Two days ago I used the guide someone posted here to help me remove my roofliner to get it redone. We can really help each other out.

But I dont see how to upload a picture here. Help me out if Im missing something.

The two modules in question are near the center part of the dash that runs between driver and passenger, and they have vacuum lines running to them on their bottoms. You remove these and block them off at their little connections on the tubes. On the top, aluminum rods reach up into the dash and attach to black plastic levers that move the vents. You really cant miss it if you just get in there and look. Its difficult to get under there and look up if you arent physically fit I understand, but you can also just take a bright flashlight and a mirror from your wife's makeup desk and look up there that way while being comfortably upright.

Good luck.

[OCKlasse]

Originally posted by nick_nolastname
I would... does this site host pictures? I dont see how to do it.

I really feel for people who own these cars and I do want to help.
Two days ago I used the guide someone posted here to help me remove my roofliner to get it redone. We can really help each other out.

But I dont see how to upload a picture here. Help me out if Im missing something.

The two modules in question are near the center part of the dash that runs between driver and passenger, and they have vacuum lines running to them on their bottoms. You remove these and block them off at their little connections on the tubes. On the top, aluminum rods reach up into the dash and attach to black plastic levers that move the vents. You really cant miss it if you just get in there and look. Its difficult to get under there and look up if you arent physically fit I understand, but you can also just take a bright flashlight and a mirror from your wife's makeup desk and look up there that way while being comfortably upright.

Good luck.

Thanks Nick. I'm a fit 22 year old, so I hope I can get the job done! :D

[OCKlasse]

OK, so I have two pics for you and two questions :D

First, is it these four vacuum lines that I want to remove and block? Any specials tricks you used? These things are on there tight!

http://img.photobucket.com/albums/v338/trefive/020.jpg

Second, how exactly did you go about removing the levers? From the top I assume? Once they are removed, do you then physically move the vents with the pliars, or hemostats as you suggested? Thanks

http://img.photobucket.com/albums/v338/trefive/025.jpg

Just don't want to screw anything up :o

[nick_nolastname]

Nice!

Those top two vacuum lines are the ones I removed, the ones going to the grey vacuum modules. Pull straight down on those light gray plugs that are the ends of the hose. They are on tight but they do pull right off. I promise. Think German! Those other two lower ones... I dont know where they go. You have to remember you aren't talking to a pro here, just a cheap hacker trying to keep his wife happy with this stupid car. This advice is worth no more than you paid for it, my friend!

Those two aluminum rods go up in there and are press fitted over a barb sort of fitting ( one for each rod ) that holds them to the black levers that control the center vents. I used a pair of 12" hemostats to reach up there and kind of twist them off the barbs. Then once removed, I used the hemos to turn the vents to the open position, where they will stay quite willingly. Try pulling down on those aluminum rods while looking up in there and you will see how it operates. If you are uncomfortable ripping that mechanism apart, you might be able to to just pull the levers down and secure them somehow without disconnecting them. I found that to be impractical because on my car, the springs forcing them up to the closed position are absurdly strong. Maybe yours will be different.

All in all a right bitch to get to based on their position and how you have to hold your body to get your arms in there.

Best of luck.

[OzC36]

Those top two vacuum lines are the ones I removed, the ones going to the grey vacuum modules. Pull straight down on those light gray plugs that are the ends of the hose. They are on tight but they do pull right off. I promise. Think German!

nick-n-l-n
Just for clarity, did you:

1. Pull the vacuum tubes off of the terminating grey fitting; or
2. Pull the grey terminating fitting from the darker grey modules?

[nick_nolastname]

I pulled the light gray fittings off of the vacuum modules. I did not disconnect the hoses from the light gray fittings.

[OCKlasse]

Well, I did it! Thank you to Nick for all of the help!

I disconnected the right pair of vacuum lines, (the other left ones control the module for getting air to the footwell area) then gave them a nice treatment of silicon sealant.

Once that was done, the vacuum modules actually dislocate fairly easy. I was then able to get a long, thin flathead up there and disconnect the end of the metal rod from the plastic unit. You just push the top of the levels to the left as it is slid over a plastic rod. I then pulled the two modules out altogether. A little tonsil-work for the 202...

After that, move the plastic levers controlling the units all the way DOWN, and recover everything!

I now get tons of air blowing through the center vents! :D Once again, Nick is the man! :bunny:

[OCKlasse]

Originally posted by nick_nolastname
I pulled the light gray fittings off of the vacuum modules. I did not disconnect the hoses from the light gray fittings.

This is what I did. You'll find it practically impossible to do it the other way without damaging the vacuum line.

[nick_nolastname]

Rock on! Glad to be of help.

[OCKlasse]

Alright, so now air comes out of the center vents, as does AC, but not heat. I will have heat coming out of the side vents, but cool air will still blow through the center vents. Any ideas?

[nick_nolastname]

I noticed that too after I talked to you. I dont know why that happens so far, havnt had time to look at it yet. We live in Florida so I'm thinking it doesnt matter for us. What I'll have my wife do is just close the center vents when she needs heat. I drove the car the other day during our brief cold weather here that we call winter, and while its true heat doesnt come from the center, the interior still got plenty hot. I think closing the center vents with the wheel on the front would speed that up if it was needed.

Sorry for your problem, I did warn you I'm just a hack and not a pro. :( If this really bugs you, obviously one of those levers we turned is the cause, and you could try turning one or the other one to see which it is. Since you were able to remove the vacuum dashpots entirely, you could buy a replacement for one or both and get that feature back. As for me, I'm going to leave it as is in our car.

[OCKlasse]

Originally posted by nick_nolastname
I noticed that too after I talked to you. I dont know why that happens so far, havnt had time to look at it yet. We live in Florida so I'm thinking it doesnt matter for us. What I'll have my wife do is just close the center vents when she needs heat. I drove the car the other day during our brief cold weather here that we call winter, and while its true heat doesnt come from the center, the interior still got plenty hot. I think closing the center vents with the wheel on the front would speed that up if it was needed.

Sorry for your problem, I did warn you I'm just a hack and not a pro. :( If this really bugs you, obviously one of those levers we turned is the cause, and you could try turning one or the other one to see which it is. Since you were able to remove the vacuum dashpots entirely, you could buy a replacement for one or both and get that feature back. As for me, I'm going to leave it as is in our car.

No worries Nick! I was just curious. I appreciate what you were able to do for all of us! :bunny:

[taz069]

Glad i found this thread!!!! OCKlasse this is the problem with my 96 c280. Good cold air outta the center vents and heat on the sides!! What did you come up with to cure this prob. I have done some of the mentioned items in this thread but to no avail. I even disconnected the duo valve under the hood to lower the temp coming outta the side vents, that helped for about a 30degree reduction. But still didn't fix the vent prob.