No air from center dash vent. Slow trunk latch. Vacuum related problem? PSE pump? - PeachParts Mercedes-Benz Forum

RProsser · #1 08-01-2007, 11:23 AM

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.

mbdoc · #2 08-01-2007, 12:00 PM

If you depress the EC button with the engine running will the center try to open?

The central locking pump (PSE) is designed ONLY to help the engine vacuum under emergency cases, MVA is the term for that help.

RProsser · #3 08-01-2007, 12:21 PM

Hi. I recently tried every conceivable combination on the climate control, with engine on and off. I note air speed increases and decreases, temperature goes up and down, but the air doesn't change where it is coming from.

With the engine off, while trying pressing buttons on the climate control, I hear small noises in the dash like servos quietly going on or off, but there is no change in where the air comes from. Note: with a flashlight I can see the center vent flaps are in a half-way position, neither fully open or closed.

97'C280 · #4 08-01-2007, 05:08 PM

I have the EXACT same symptons and issues...can somebody please help us out in here...for cryingout ****ing loud..

HELP

RProsser · #5 08-02-2007, 10:14 AM

From my searching this site I see we are not alone by any means. And, it is not specific to 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 help by doing their own search. I've been unsuccessful using words like: "w202 AND climate control AND air vent AND PSE pump."

Wouldn't hurt to also try www.mbworld.org and others I may not be aware of.

TX76513 · #6 08-02-2007, 10:58 AM

In the W126 class it's the vacuum pods which can be checked with a mity vac. While the pods themselves are somewhat pricey you can purchase the diaphragm rebuild kits for about $6. There is quite a bit written about the older vehicles and like this your thread mentions - it's light on some of the younger benz (similar) problems that may just now be developing. Do a search for "vacuum pods". There is some good information that is probably relevant to the newer models.

RProsser · #7 08-02-2007, 11:49 AM

Thanks for the comment. I agree that this is probably a burgeoning problem, now making itself known on the newer models.

And I did a search as you suggested using "vacuum pods AND air vent." It returned a lot of interesting results with very similar symptoms.

However doing a search for "W202 AND vacuum pod" gives zero results. Finding a step-by-step procedure to fix this problem on the W202 C230 / C280 / C36 would be great!

(I still have no idea if my slow trunk latch, as described at the top, is related or just a secondary problem.)

TX76513 · #8 08-02-2007, 11:58 AM

Let's move on to the next step. Make contact with George who has taken over the supply of repairing these pods and may have the knowledge to share for the newer models. I have always thought of George as a vacuum guru

George Murphy

Performance Analysis Co.
969 Oak Ridge Turnpike, Suite 258
Oak Ridge, TN 37830

865-482-9175 9 am to 5 pm ET M-F

juribe2 · #9 08-02-2007, 12:05 PM

I had a similar problem in my w124. Firs I thougt it was something related with those vacum pods but then I noticed I had more vacum problems (not only central vents operation). In my case, the rear head reast were not deploying. Finally, my mechanic found a disconected vacum hose behind the engine block, close to the oil filter. Looks like someone accidentally disconected it when doing a filter change. It was an efective and free fix.

RProsser · #10 08-12-2007, 01:02 PM

Juan, thanks for your tip. Armed with that info, I checked the headrests and, as yours, they didn't retract. Seems we're on to something! Next, 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 energized the ignition and hit the head rest button. Nothing. I started the engine, and hit the button again. Down they went! Next, 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. Get this: 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.

juribe2 · #11 08-12-2007, 11:26 PM

Well, that's funny. At least you found that vacum hose and didn't had to dismantle the dash to fix the actuators.

Bio300TDTdriver · #12 08-12-2007, 11:44 PM

So MB was still using vacuum pods in '97? There is tons of info on here about them failing in the 124s, but they are 20 years old. The default position on the 124 is the defrost vents, so when the pods fail that's where the air goes. It really sucks if they are failing after 10 years.

Chris

whunter · #13 06-20-2012, 07:35 PM

for customer

ryno365 · #14 06-20-2012, 09:35 PM

One though for diagnosis: get one of the hand operated vacuum pumps (I picked one up at an autoparts store for a few bucks). From there you can attach it to the vacuum controller under the dash (this is just in my experience with my W124) and test how well the pods hold a vacuum and if they still operate. I too had the problem where the vacuum lines that connect right at the driver side firewall were disconnected. My gremlin with A/C now is a slow leak and a blower regulator that seems to have packed it in.