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  #1  
Old 06-15-2009, 02:04 PM
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Air always coming out of center vents - not holding vacuum in "0" position. w201

Hello climate control experts. This is my first foray into fixing my climate control problems. Here is how I have tested the vacuum on my 1992 190E 2.6:

I took the green and red striped vacuum line by the fuse box and pulled a vacuum on that line with my Mityvac, while going through each vent position on the push button unit. All of the vent positions hold vacuum except when the pushbutton unit is set to the "0" / off position. It doesn't hold any vacuum nearly like the line is disconnected.

Another symptom is that when the system is in the "0" position, the blower fan is off like it should be, but air comes gushing through the vents when the car is at speed.

What pod / vent controls this? Is it the main air flap or recirc pod? I am not sure where to start, and I'm a bit new to all of this. I also have the clicking noise behind my glovebox and heat out of the side vents ONLY when the car is at load. I have checked the other engine related vacuum lines and there are no leaks, I have replaced most of the vac lines and rubber in the engine bay.

Any ideas? TIA.

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  #2  
Old 06-15-2009, 04:45 PM
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When you select "O" on the a/c panel the fresh air vacuum element is the ONLY one that gets vacuum.

Vacuum leak would be the answer.
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  #3  
Old 06-15-2009, 05:59 PM
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Quote:
Originally Posted by M.B.DOC View Post
When you select "O" on the a/c panel the fresh air vacuum element is the ONLY one that gets vacuum.

Vacuum leak would be the answer.
Hey MB DOC,

Thanks for the answer. It's definitely leaking or not connected. I guess my question is where is the fresh air vacuum element? Is it a pod which operates a flap? Is this also known as the recirculation pod? From my searches, there are numerous pods, some that require the whole dash to be removed in order to replace them. I was hoping to find out which one this is and where to access it since I know it's either disconnected or faulty. Would you be able to point me in the right direction please?

Thanks.
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  #4  
Old 06-16-2009, 08:04 AM
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That vacuum element is at the bottom of the heater case.

Removal of the center console is required.

Takes me about 1.5 hrs to do that (20+ times).
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  #5  
Old 06-16-2009, 01:04 PM
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Thanks Doc. Will tackle it this weekend possibly. But will allot a few more hours to it.
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  #6  
Old 10-21-2009, 06:32 AM
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Is this issue fixed?
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  #7  
Old 10-22-2009, 01:34 PM
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Yes, and no. I pulled out the switchover valve and tested each vac line going to each pod. The fresh air pod was completely dead. So I just plugged it at the switchover valve. Not a real solution but at least to the engine it doesn't see a vac leak. The fresh air flap is still open though and I haven't yanked off the dash to change anything yet. One of these days, maybe when the heater core leaks.
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  #8  
Old 10-22-2009, 02:06 PM
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Fresh air pod

I have spent some time removing interior parts to know you have a job ahead of you. Like MB DOC said, it takes him 1 and 1/2 hours to do the job. I would allow at least 5 hours. The first hour to drink a few beers just to prep. The last hour to admire your work. haha
Best to take out the console. The pod, as MB DOC stated is below the heater. When you get the console out, look behind where the ashtray used to be. You will see two pods. One in front of the other. The fresh air, if memory serves, is the one tucked in the farthest.
As you are removing things, check the plastic vac lines. Make sure one has not disengaged. May save you some time if the pod is really not the cause.
There is one pod, the blend door pod, that is located on top and center of the HVAC. This one requires the dash to be removed for access. It also has an electrical lead. Not sure of it's purpose. Maybe a positioning sensor.
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Air always coming out of center vents - not holding vacuum in "0" position. w201-mercedes-2442.jpg  
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Last edited by cdplayer; 10-22-2009 at 02:07 PM. Reason: spelling
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  #9  
Old 10-23-2009, 05:18 PM
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Ok here's my 2¢: I don't know anything about an hvac or switchover valve (????) nor do I dispute what MBDOC or Cdplayer are saying as they have both personally given me advice and even walked me through repairs over the phone, but I had a similar problem and it was the heater valve located on the right side of the battery on the passenger side. I tested it by removing the valve, which is fairly easy because its only connected by 2 hoses. I lifted up on the flap of the valve to where it should've been closed and I blew through the one end and air was coming out of the other end which was not suppose to happen. I later ran water through both ends with the flap open and supposedly closed and water still flowed right through it. My temporary solution was to cover both ends of the valve with electrical tape and pennies over the ends and hook it back up, this way I atleast stopped the heat from coming out simultaneously as the cold air from the a/c. However, I still have not yet bought a new valve yet, but so far so good. You might wanna check the valve and see if its working or not.
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  #10  
Old 10-23-2009, 08:17 PM
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Yeah I have replaced the heater valve already. Mine actually leaked a bit of coolant. Vac line to it was fine too, checked with a Mityvac. I think one of the symptoms of that ishot air out of the side vents all the time, which wasn't exactly my case.
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  #11  
Old 10-24-2009, 02:48 PM
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I am having the same problem it sounds, I wasn't sure where to start to try and figure it out, now I have some ideas, thanks!

I do have a question though, I don't want to hijack this topic by any means, but Ismalley made a comment about an area I have a damaged piece in, and I was hoping to get some info. The area behind the battery on the passenger side, there is long piece of plastic that seems to run along the firewall across the length of the engine compartment, you would have to remove it at least partially to get to the components behind it... Does anyone know what this part is called? Mine is broken and so far my attempts to find any info on or about that piece have got me nothing.

Thanks, and sorry about posting a question on your topic Chowbow.
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  #12  
Old 10-23-2012, 12:02 AM
Gemsbeme
 
Join Date: Oct 2012
Location: Kent,WA
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I had the same issue (cold air blowing through center vent at speed even with blower motor turned off) on my 1993 W201 with 150k on it.
What I did was pull out both center vent grills (grab with pliers protected by cloth on each side of each grill then pull each side loose and out)then remove center panel (4 screws 2 top,1 of these is accessable after pulling rear window defrost switch, and 2 bottom) also a hex head screw just above the lever (inside the slot) in the center of the 2 grills,then work the panel out.
My problem was the connector from the center lever to the flapper door was broken and thus not closing the door when the lever was pulled down and allowing the cold air in.after replacing connector (wrecking yard part) replace in reverse order.
hope this helps anyone else with a similar problem

Gemsbeme
1993 190e 2.6 auto 150k

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