middle vent air flow - PeachParts Mercedes-Benz Forum

JHZR2 · #1 01-13-2003, 10:54 AM

Hi,

I have searched and found info regarding airflow problems with the footwell vents. Unfortunately, my problem is only with the two middle, upper vents in my 300D. In the summer, I was driving on a long trip, aqnd shanged the AC flow from the third button from the right to the fourth button from the right (going from all upper vent flow to bi-level flow, I believe). Anyway, after changing it back, only air has been coming out of the far right and far left dashboard level vents. Very little air comes out of the middle two. It was really quite random, how all of a sudden they dont want to work.
So, I am guessing that the problem lies either in the little connector tubes, a check valve perhaps, or a stuck air diversion flap. However, I am not sure how to get to the equipment that controls those flaps, nor do I know how to get to those two flaps.
I assume it requires removal of the glove box to get to those vents from the one side, but from the other???

Any help on this would be most appreciated. I need to put together a fastlane order anyhow, so if I could get reccomendations on what parts I would probably need, or that I should consider ordering, Id appreciate the information.
Thanks

JMH

md21722 · #2 01-13-2003, 11:06 AM

By DESIGN the dash center vents are for COLD AIR. HEAT should NEVER come out of the center vents. Heat should come out the side vents and the floor. That's the way it is on 124s - your 123 MAY be different.

JHZR2 · #3 01-13-2003, 11:11 AM

OK, thanks for that info... The thing is, the center vents would not work in the summer to blow AC air through. I am only deciding to fix it now, because I need to repair the monovalve, and might as well devote some time to the climate control (and buy any required parts) while I'm at it...

Thanks

JMH

lrg · #4 01-13-2003, 02:24 PM

Likely a 99% probability that the rubber diaphram in the vacuum servo that works the flap for the center vents is bad. Oftentimes they split on the edge in such a way that they will still (infrequently) work. Best way to check is to use a MityVac to pull a vacuum on the line to that servo a few times to see if it will hold. Access to the servo is either by removing the dash or through the glove compartment. These units frequently fail first due to heat drying out the rubber diaphrams. There are lots of threads on this topic that will tell you everything you need to know. The parts aren't that expensive but the installation can be a PIA, not hard just time consuming.

#5 01-13-2003, 03:12 PM

I replaced one of my center vent diaphragms last fall, and I had struggled for a while to do it through the glove box opening. I could have probably removed the bad pod, but adequately reinstalling the newly rebuilt one, and attaching the control rod would have been impossible in my opinion. I do believe there are quite a bit of things that can be done through the glove box, but I could not complete the diaphragm replacement. I decided to remove the dash. It turned out that it was much easier than I had thought, and I wouldn’t hesitate to do it again on one of my other cars.
Below are a couple of links that show the diaphragm and it’s location with the dash removed. It is an intimidating job, but one that than easily be tackled.
Good Luck!
Robert

http://home.attbi.com/~frickfamily/Dash-1.jpg

http://home.attbi.com/~frickfamily/Dash-2.jpg

JHZR2 · #6 01-13-2003, 04:15 PM

thanks for the info and the pictures... Wow, definitely intimidating to do. As I don't have an inside place to do this work, itll definitely have to wait until the spring/summer. But, I was thinking, as a fix that might be OK, and allow me to have working center vents until I can take out the dash (and afford to buy all new vacuum pods, and anything else that would possibly need to be replaced under there, so Ill not have to repeat it), I was thinking this:

I am curious if there is a way to force the door that allows air out the center vents to stay open. Assuming the vacuum pod is busted, it shouldn't reclose or anything, and so long as vacuum is held by the resty of the systems in the car, its OK. Since its always open, I would guess that anytime the blower is on, air would be going out there, but I can close them at the dash vents.

Would this pose any sort of problem with the operation of the rest of the system? I dont care about comfort of hot air blowing out of the center vents, or anything like that, as like I said, Ill just close the vents in the center at the exits. But I don't know if anything else that is working could get messed up, or if the door directs flow in two ways, depending on the way the door is oriented.

Any comments or ideas on this would be appreciated.
Thanks for your time

JMH

gsxr · #7 01-13-2003, 06:45 PM

Brian is right, the 123 & 124 operate the same way. Only cold air comes out the center. In the winter, forget about them, you should get hot air out the side, floor, and defrost. If you want to force the center vents open for A/C in the summer, it can be done - I did it. I stuffed my hand back there with the glovebox out and forced the pod to open the flap, then stuck a screwdriver into one of the center vents to jam the flap partially open. Then you don't touch the screwdriver! It's ain't pretty but it does work (got my wife through this past summer.) I need to pull the dash & fix the stupid pod properly.

Never done a 123, but I've done three different 124's, here's the photos of that - plus photos of the failed rubber bits:

http://www.meimann.com/images/mercedes/W124_dash/

Regards,

The Warden · #8 01-13-2003, 06:50 PM

My car has a similar problem, I believe. The previous owner's response was to take a glass stirrer and put it partially into the open door, to keep it open. This stirrer is currently partially sticking out of one of the vents, so it's unfortunately obvious that it was jury-rigged, and also, that vent can't be closed now. I think that this has compromised the performance of the defroster, as now air is coming out of the center two vents at all times (if I remember right, air's only supposed to be coming out of there with the CC switch in the center or the left-of-center position). I'd like to someday go in and fix this, but I'm a bit apprehensive since I haven't dealt much with vacuum systems.

OTOH, now's a perfect time to do it since my car's down for the count right now anyways...hmm...

#9 01-13-2003, 07:58 PM

Okay,
Here is what I did for the intermediate fix. I used a small (about 1-1/2") C-clamp, and through the glove-box opening I clamped the damper operator to the full open position. This worked for sometime until I was ready to tackle the full replacement.

Robert

gsxr · #10 01-13-2003, 08:14 PM

I was quoted ~$1000 at the dealer to replace the center vent pod only on my 124 chassis (87 300D) about 3-4 years ago. I'm sure it would be similar today. Now that I've done the job 3 times - replacing ALL the pods, not just the center vent - I can do it much faster. Shoot, I'll do anybody's 124 chassis for $500, parts & labor, for all 7 pods - you just need to get your car to Boise, ID!

I wonder how the 123 will compare if/when I get around to doing that one.

Stevo · #11 01-13-2003, 08:54 PM

Seems I read a post a while back about someone that cut a HOLE through

the DASH above the offending servo and because they used a Coverlay to cover the real (cracked anyway) dash no one knew. I would think a 4 inch grinder with the right blade could save allot of time and work