1997 C280, well maintained, 110K mi.

The center dash vent no longer flows air -- air only flows from the defrost and side vents.

When it was only an occasional problem, once in a while you'd hear a high pitched whistle coming from behind the dash. Also acceleration or deceleration could affect air flow from the center vent.

Research shows this to be a fairly common vacuum problem, but the fix gets vague. I though it's worth getting in to again here.

I've read that the problem can be caused by a faulty "PSE" air pump. Mine is located near the right rear brake light cluster.

Some people with this same air vent problem complain that their PSE pump is constantly on. Mine seems to come on and off as it should. However, this may be a clue: when pressing the trunk release button inside the car, the PSE pump runs, the trunk pops up and, after a few seconds, the pump stops. Problem is, the trunk will not close again for about 20 seconds. The latch mechanism does not release to allow the lock to engage. After a few attempts, the trunk will finally slam shut.

Could the inop center air vent and trunk latch be related? Does this point to a vacuum leak behind the dash?

Any help would save me hours and hours of troubleshooting.

Thanks in advance.

Bob in San Diego

I never thought this would be a common problem; there's no air flow from the centre vents of my '94 C280 either and I'd really want to know why. I don't know if it's useful to mention, but each time after I use the A/C I hear a very annoying noise coming from the passenger side vent. It's like "bzzzzz bzzzz bzzzz" as though there's a small vibrating stone in there or something. This can be heard only when the car is moving. Sometimes the noise goes away after not using the A/C for a while... Maybe there's indeed a stone in there, maybe it's a loose screw, maybe something related to the pump, not sure.

Anyways, I hope someone knows why exactly this is happening.

That "bzzzz" you describe ... I had what sounded to me like a leaf stuck in a vent, fast air blowing over it, and it vibrating like a reed. Perhaps we are describing the same thing.

From my searching this site I see we are not alone by any means. And, it is not specific to the W202 C-class either. Problem is, I cannot find anyone who has described the fix. Often these complaints go unanswered.

It's time to get busy and find the remedy.

I invite anyone who reads this, who is motivated by a similar problem, to contribute by doing their own forum search. I've been unsuccessful using words like: "w202 AND climate control AND air vent AND PSE pump." Maybe I am missing something.

Wouldn't hurt to also try www.mercedesshop.com or others I am not be aware of.

i have the same problem somtimes the center vents you feel like the air goes under the dashboard and the air comes from the 2 sided vents

????


i 've cleand the AC filter by self i opened it . the quantity of airflow is more .. now it's a bit better but the major problem comes and goes


any advice !!!


thanks in advance

Can't someone go to a mercedes shop and ask them what it is? I went there for similar noises but I only got them when my heater was turned on, and my dealer told me not to worry about it since it was not that big of a problem.

i took it to many repair shops.. but they couldn't diagnose it


mercedes dealer over here will take 350$ just to check it up
it's too expensive

I am quickly learning that this is a common malady with other models and that this problem may just be now making itself known on newer C-class W202s.

I did a search with the terms "vacuum pods AND air vent." Not much on this forum, but MercedesShop.com returned a lot of interesting results. I found similar symptoms, however the repair on a W202 may be different. Finding a step-by-step procedure for the C230 / C280 / C36 would be great!

This is the bible:

http://www.savefile.com/files/627256

I had a C280 and it made me hate Benz. Well, not really hate but it had so many problems I thought it was the poster child for lemon benzes. While visiting the shop so frequently, I saw that reliability issues were not just the thing for C-classes, it's all of the models.

Let me see, I had an AC problem but don't remember the fix. Threw away all my repair receipts when I dumped the car.

Good luck!

Luckily my car has been problem free for the most part. I think it may have something to do with my mother driving it for the first 9 years of the car's life.

Check the vacuum line in the engine compartment. in the rear passenger side of it

E55, thanks for your tip. Armed with that thought, I looked for a disconnected vacuum line at the firewall. Nothing on the passenger side (checked gray and green vacuum lines), but when I followed the gray line over to the driver's side, past the oil filter and under the intake manifold -- ah hah! -- it was disconnected (thanks no doubt to some knuckle-dragger at Jiffy Lube).

Time for a test: I started the engine, and tried the air-con controls: I cycled through the air-direct button and, for the first time in many months, I was greeted by a blast of cold air from the center vent. Yeah!

However, after a few minutes, and more cycling tests, the air stopped coming out of the center vent. As far as I could tell, everything else still worked (including the head rests). Darn!

I though the vacuum line had come back off. Nope, still connected. I tried driving it around the block, going from light- to full-throttle, with speeds up to 60 MPH. Nothing.

It's odd that the center air vent worked for two minutes, then quit again.

An hour later, I remembered that my trunk latch was also not working quite right -- apparently also a vacuum problem, and who knows, possibly related. That symptom: if you pressed the center console button to pop the trunk, you had to wait 10-15 seconds for the PSE pump (right rear quarter panel near the tail light cluster) to stop humming before you could close the trunk.

So anyway, I went back to the car to try the trunk. No change. Then I started the car. Instantly I had a blast of cold air from the center vent! What the ...? I cycled through the system over and over, all air vents worked as they were supposed to -- at least for now.

I'll let you know how it goes, and if some Mercedes-Benz guru here can explain why this happened, I'd really like to know. Thanks.

There is a vacuum resevoir in the right front wheel well that can leak

That's a nice tip/hint, but can you give a little more to go on? For instance, how you get access to it, e.g., from under the car, from behind a wheel well panel, from inside the car, etc.

behind the wheel and behind the inner fender liner