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1996 S320
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Discussion Starter #1
Hello all:

I have a 1996 S320 and here lately my air out of the fronts vents go from coming out to just stop working and coming out of the defroster.Then go back to coming out of the vents again. I really notice it when I stop and take off. It feels like a vacuum issue but I don't know where to go for this. Could someone help please. Pics would be nice to.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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I am not sure if i completely understood you, but so far you did not persuade me that something is really wrong. As far as I know if you have activated AUTO buttons (the largest ones) then it is normal that air is changing its flow direction according to some algorithm which I believe is not so simple.

Anyway, there is so called flap test, you can perform it. Mike posted it in my latest thread here. Just search here for my recent posts and you will find instructions ... I am just not sure if they are ok also for 96 year. i suggest you to try.
 

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1996 S320
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113 Posts
Discussion Starter #3
AIR Vent looses air as I accelarate with the air condition on

My mechanic and I figured out what cause this problem. As I have my air condition on face blowing, as I take off to accelrate I loose air out of the face and it comes out of the defrost vents. We traced it back to the Y11 block and the K30 relay. Nothing everything worked so I asked him where is the location for the main vacuum for the engine. It is located on the passenger floorboard on the right side. There is a black block with around 5-6 lines coming from it. Primarily the main vacuum line. That block somehow was bleeding air somehow. We believe the checkvalve inside was bad. So we cut the line in-two added a checkvalve in the middle.And DAM IT WORKED. Nomore loosing air out of the vents during accelration. I am writing this in hopes it can help someone out in this situation because it has frustrated me for 2 dam weeks. Keith from raleigh nc. Benzworld forum is the dam best. I have learned a great deal off of this site.


PS my car is a 1996 S320 SWB
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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Are you talking about y11 switchover valve block? I think it has more than 6 lines but anyway ... I also have similar problem with flaps. I found out that there is no vacuum on line 13 which comes into the block Y11. This line is fed by vacuum reservoir at the front right wheel, so evidently that one does not have any vacuum inside. Now I am researching where the line from the reservoir leads. I assume that somewhere to the intake manifold of the engine. someone has any instructions?
 

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92 500SEL to 01 E320T current 2014 lexus LS460
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The reservoir is fed from two sources, the first would be from the engine, except when off or accelerating. The second would be the PSE pump which would provide vacuum in the lack of the above conditions.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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The reservoir is fed from two sources, the first would be from the engine, except when off or accelerating. The second would be the PSE pump which would provide vacuum in the lack of the above conditions.
I see. So if the line from PSE to the Y11 block or reservoir respectively is not crucial for flaps if engine is on?

namely, my flaps hinder airflow in HVAC, there is no leak in y11 (under the dash) and distributor (at footwell), gray line from distributor to intake manifold provides vacuum. maybe I have a leak but I cannot detect it with "mouth to line" test. is this possible? should I get more serious tester?
 

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1996 S320
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113 Posts
Discussion Starter #7
Low vacuum

I am the guy who started this thread. If you could explain your original issue. Under your rear seat you have a PSE pump that controls air(Vacuum) to your flaps. Check that. Until you tell me your original problem, I maybe can help hopefully. I know how you must feel.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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Hi there. Yes I am sure that you know ho do I feel, however I am frustrated because there is no logical explanation.

Yes I have alldata but I do not think it is the best service ....

It is of course hard to say what is wrong in your case, but I am only in a position of guessing like in my case. so I feel that your trouble is too low vacuum in the system which is fed by PSE (connector 6 at the footwell distributor) or by engine intake manifold (connector 7). Then from this connector line 5 leads to switchover valve block Y11 behind the glove box. most probably your distributor block is damaged and you have a leak. I do not believe that PSE pump line is crucial. beside that if something is wrong with this line there is a valve in the distributor block which prevents leaking losses. see the attached picture for the distributor block. I also found out that vacuum reservoir actually is divided into two parts. the upper one has output hose from distributor block (black-gray line) but it is for transmission. The lower part of the reservoir is for AC (red-gray line). that's all. as one can see when line from manifold creates vacuum then it also feeds vacuum reservoir and switchover valve block Y11 in the same time. once again, I think that vacuum from engine should be sufficient for AC flaps functioning. I cannot imagagine that MB designed system to be constantly supported by PSE (line 6). I also read here that PSE cooperates in controlling the flaps, but I am 99% sure that it is only in REST mode when the engine is off or in extreme situations when engine produces low vacuum = acceleration.

My problem is strange:
-in REST there is no heat (minor problem)
-the higher the preset temperature on AC unit, lower the airflow through vents. I can hear how there is enough power in blower, but air is just bumping into (closed .. half-opened) flaps. removing cabin filter improves situation but not dramatically. I am also aware that when low temperatures are selected then main flap is closed and recirculation flap is opened. in middle range of temperatures the main flap is half-opened (or 20% ... whatever) and recirculation flap is opened. In high temperature range and in defrost mode main flap is fully opened and recirculation flap is closed 100%. i also performed flap test and I can say that in general flaps are responding to the LO in HI which are shown on a display. the problem is still here if i completely remove the housing of the main flap above the filter, thus eventually blocked flap (closed flap) when high temperature range is selected on AC controller, is excluded from story.


i will do the folowing test: I will connect connectors 4, 9 an 10 on my distributor block ... they seem to me like empty test connectors. or I will simply join lines 7, 5 and 13 to see if I have problems with distributor block. by the way i replaced Y11 to see if there is a problem but with the another one from another car the problem was still here.

the following is very strange:if there would be some leak further from Y11 which feeds flaps with vacuum, then this problem would be greater for low temperature range, because in this case main and recirculation flaps are engaged. can you see how funny is this? but the problem with airflow comes in higher temperature range where (let's say so) both flaps's lines are without vacuum, because the Y11 block does not open the path for vacuum into the lines which feed both flaps ....

Now I assume:
-vacuum reservoir at the front right wheel is crucial for flaps functioning (most probably it is ok, however the red-gray line to it must be checked)
-PSE pump and line 6 are not crucial for flaps when engine is running. Disconnecting line 6 from distributor and clogging the opening on a distributor can help in diagnosis.
-somehow I must connect lines from distributor's connector 5, 13 and 7. if the system will work, then distributor block is a culprit. if not, then separate lines must be checked. the problem is that i do not have a vacuum tester.

any idea?
 

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1996 S320
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113 Posts
Discussion Starter #10
Vacuum issues.

I have a great mechanic. First let me ask you do you? Did you hook up a star diagnostic computer to your a/c on board computer? Because he done this for me and that was pretty neat. It gave us voltage readings, pressure on low and high side, he was able to manually open and close flaps, even half way or partically open or closed. But that computer can do alot of things to help troubleshoot your problem I would have someone do this for you. Like you said it can get frustrating and spending unessarry money not to mention loss time. That was what I had done when we diagnosed it back to that block on the side of the passenger footell. Keep me in formed buddy.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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it seems that i am totally out of my mind, i did not notice that you solved your problem already. is it coincidence that I am dealing with my problem 2 weeks, too?

tomorrow i am visiting my mechanic. of course he has diagnostic system. the only problem is that for last several tries we did not succeed to get into car's computer: connection cannot be established. like in old days with modem internet connection.

I have found another ground module with same catalog number. i do not know anything about electrical part of this car but maybe my ground module is damaged and the replacement will work at least to diagnose the flap problem.
 

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1996 S320
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113 Posts
Discussion Starter #12
Vacuum issues.

Where are you guys trying to link in at? Inside under the dash, or under the hood on the passenger side? We linked to the one under the hood. You are right the one inside under the dash tells you did not establish connection. Do not use that one.Keep me in informed buddy with your progress. My wife and I are going to our beach house in Myrtle Beach SC next weekend and knowing the air is right was very critical to me. But it all started when I replaced a bad evaporator. Man was that expensive. I've heard about people putting shit in the system but I was like no I was going to get this fixed. anywho keep me updated if I can help let me know.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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of course, the 38-pin connector under the hood is the proper one. i even do not know that there is something under the dash. my mechanic is ok, he deals only with MB and has a tradition. mine problem started on the same day when the car was on regular maintanace (oil, filter ....) or the next day when I replaced catalyst.

I was starting to get very inconvenient ideas like what if the polarity of my blower motor changed and now it is spinning in wrong direction? there is no more normal explanations for what is happening. Namely if air flow is ok in LO (cooling) or with recirculation flap engaged, then this is a strong indicator that path through flaps is ok. i have appointment with my mechanic in 1 hour.

the result: mechanic does not know what it should be for sure but most probably the flaps near the evaporator and heat exchanger are damaged. I do not know where exactly these flaps are, I even did not know that they exist and by what are they driven (pneumatic or electromotor). it seems that the problem is serious ... a lot of work and big costs. he entered the computer of AC but he claims that he cannot manually control flaps. he will contact AC expert and then I will make a decision: to repair it or sell the car (it is a pitty because it is well maintained car in a good shape, i took care of each detail and reapired it soon as it shown).
 

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Today I checked if vacuum reservoir is ok. it is. It holds vacuum ca 0,6 bar. I checked each vacuum actuator for flaps and each holds vacuum. I also directly connected vacuum maker device at the start of line 5 (which goes into switchover valve block y11) and tested what happens with vacuum when different options on AC controller are pressed. Everything is ok. So there is no leak in distibutor, no leak in valve block, no leak in vacuum reservoir and no leak in vacuum actuators. The vacuum pressure which comes from intake manifold is the same as in some another 500 SE with no problems.

Was this car designed to force people to make suicide or I just have extremely misfortune? What did happen that both sides of my HVAC have difficulties in airflow? if there is a mechanical faulire of flaps, is it possible that it happened in the same time on both sides of HVAC? What is the chance for this ... 1:1,000000 or less? Both sides of HVAC reacts eqaully on changes of buttons on AC control unit.

Does anybody know what is the design of HVAC? How close the evaporator and heat exchanger are? Is there any flap between them? If yes, is there one flap or two flaps (left and right). But even if there are two flaps there is extremely low possibility that both failed in the same time. so the only logical conclusion is that the air is blocked somewhere right after evaporator or before it.

There is one more possibility: there are two baffles near evaporator. One is above it and another at its side right at the blower. It is possible that that one above evaporator moved and felt between heater and evaporator.
 

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1997 S280
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Realise this is an old thread, however it came up in my search today.

The centre front vents did not work. The rear floor mounted vents did not work. Air only came out of defrost vents and two front vents by doors.

This was fine by me for a while. Until today.

I decided I was going to replace the re-circulator filter and install carbon to help with odors. After a trip to the aquarium shop and about $15 later I had thick foam carbon and installed it.

This is when I noticed the re-circ flap did not actually open! Now after going to all the trouble of replacing the filter there was no flipping way I was going to walk away from this one.

I removed the mat, peeled back the carpet, removed the side wall and a large metal plate held in by a couple of plastic bolts. "Oh crap that looks complicated" was the first thing I said.

With ignition on I tested the lines and all seemed to be okay. I reset the pump, but could not remember what fuse so just unplugged the loom from the pump itself. There is a larger white/clear line running to the distribution block for the flaps and the line powered up when the A/C was turned on. The pump timed out and locked out the line again. This time, I pushed my thumb down onto the connector on the pump - re-circ flap opened and stayed open! Brilliant, just a dodgy connection. I removed the connector and using a short length of car brake line I pushed it onto the pump and inserted the cut line inside. Reset the pump again.... 100% operation ! ....as I was leaning in the back I noticed the floor vents blowing air! Then when I checked the front, the centre vents blow air too! Now when I change the direction arrows on the a/c it actually does it instead of nothing!

I could not believe how one air line could have shut down so much of the a/c functions !

...I sat in the car with engine on, playing around.... for AGES once I fixed it ! So happy !! ! ! haha!
 

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Dead front center A/C vents, s500 1996.

Hi Jeremy,

"I removed the mat, peeled back the carpet, removed the side wall and a large metal plate held in by a couple of plastic bolts. "Oh crap that looks complicated" was the first thing I said".

Where did you do this? Which mat?
 

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Mercedes S500 - W140 && S500 W220.
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This is an old thread and a recurrent topic anyway.

Can some one please post steps or even better diagram on how to debug the
vacuum lines ?

I have a leak some where under the right front passenger seat, which I can "hear" but can not find, AND my AC is not blowing out full force.

Strange enough, it blows fine in the night, however during the day the air speed is a real drag.

Mods / elite members, any info / diagrams on W-140's vacuum lining please ?
 

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1987 230E silver W124 (sold). 1991 W140 400SEL silver.C280 W202 Silver (RIP) 2006 W203 C220 CDI
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Photos would seriously help us blokes in a similar situation....

Ben
 
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