Relationship between intake manifold, PSE pump, and air vents - Mercedes-Benz Forum

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Old 06-23-2013, 08:39 PM   #1 (permalink)
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Date registered: Jan 2012
Vehicle: 2001 E320 Wagon; 2002 ML320; 2006 S350
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Relationship between intake manifold, PSE pump, and air vents

I was curious about the air vent flaps and starting taking things apart and followed various vacuum lines. I found out there is a relationship between the intake manifold, the PSE pump, and the air vent flaps. Below is a diagram with lots of picture of how these parts connect to each other. Afterwards, I will discuss my understanding of why they are connected to each other and how they work.



Locations and points of reference:
- The dashpot (#100) is located in the front passenger wheel well
- The distributor (#85) is located behind the outer side panel of the passenger foot well
- The switchover valve block is located under the glove box
- The PSE pump is located under the rear seat (next to the car’s 12V battery)

Below are the dashpot (#100) location pictures:




The green line on the dashpot (see picture above) connects to the distributor (#85). The grey line eventually goes to the back of the intake manifold, but it first goes to the engine compartment and connects to some sort of plug that just extends the vacuum line to behind the firewall. From there, it comes out from behind the firewall to the back of the intake manifold:



Above you can see the vacuum line connecting to an adapter that just extends the vacuum line to behind the firewall.



The above picture shows the vacuum line coming from behind the firewall (see plastic vacuum hose on far right of picture) connecting to a rubber hose then connecting directly to the back of the intake manifold where the vacuum assist port is located.

Getting back to the dashpot. The green line connects to the distributor (#85). The distributor is located behind the right plastic wall in the front passenger foot well:


In the above picture, the green line on the top of the distributor goes to the dashpot. The green line on the bottom of the distributor goes to the Switchover Valve Block (located under the glove box). The clear line on the bottom of the distributor goes to the PSE pump port labeled SRU (Manifold Vacuum Assist).



Above is a partial picture of the switchover valve block and the green vacuum hose that connects the switchover valve block to the distributor. Sorry for the bad picture, but it’s the only one I have. The green vacuum hose is not connected because I was documenting some work because I had broken connectors at the time. Anyway, you get the idea.



Above is a picture of the PSE pump which is located under the rear seat next to the car’s 12V battery. The clear line from the distributor (#85) connects to the SRU (Manifold Vacuum Assist) port on the PSE pump.


So, why are these components connected and how does all this work?
From what I can tell, the main reason these components are connected to eachother is to provide vacuum to control the air vent flaps.

Here’s a good explanation of how the air vent flap system works:


When you press the button on the climate control module to change the direction of air flow (for example, from the windshield to your feet), electrical signals are sent to the switchover valve which will open/close specific valves to control specific vent actuators. Opening/closing specific valves by itself does not open/close the vent actuators. The vent actuators are opened when vacuum is present on the line.

There is a vacuum line connected to the switchover valve. When the switchover valve opens a valve for a specific vacuum line, vacuum becomes present on that line which opens the actuator (and thus the air flap). When the switchover valve closes the valve, vacuum is removed from the line and the pressure on that line returns to atmospheric levels. This closes the vent actuator (and thus the air flap).

Of course, there are two sources of vacuum: The intake manifold and the PSE pump.

When the car engine is running, the intake manifold will provide the primary source of vacuum. When the car engine is not running, but the ignition key is in position #2, the PSE pump provides the primary source of vacuum.

There is also a dashpot located between the intake manifold and the switchover valve and PSE pump. I'm just guessing, but I think the primary reason for the dashpot is to zone the intake manifold line from the PSE pump vacuum line. If the car engine is not running, the PSE pump provides the vacuum. If the dashpot wasn't there, the PSE pump would run forever unsuccessfully trying to achieve a constant 17psi vacuum.

I hope this helps you. I rushed a bit to put this together to help answer someone else’s question.
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Last edited by todd_raleigh; 06-24-2013 at 06:40 AM.
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Old 06-23-2013, 09:37 PM   #2 (permalink)
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nice bit of detective work Todd. I'll have to have a look and see if my wagon is the same.
thanks very much.
cheers
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Old 06-24-2013, 04:24 AM   #3 (permalink)
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Thank you very much for sharing this with us. It will be very handy to have this info; when troubleshooting. Lets add this to stickies ...
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Old 06-24-2013, 05:37 AM   #4 (permalink)
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This research began last year. Two separate events at different times brought this information together. The first event started when I was having problems with my PSE pump. I noticed it running constantly until the car engine started. I couldn’t find hardly any information about the issue I was having. Come to find out, the tubing infrastructure within my PSE pump had cracks and couldn’t keep constant vacuum. Here are some links that provide good detail about that event:

http://www.benzworld.org/forums/w210...ode-b1439.html

http://www.benzworld.org/forums/w210...king-pump.html

The second event started out of curiosity. Based on the air vent flap test procedure, it appeared that some of my air vent flaps weren’t opening.

http://www.benzworld.org/forums/w210...ho-can-do.html

I started researching how the air vents operated and came across several documents. After testing the switchover valve block with my hand held mightyvac and tracing the green vacuum line to the distributor, and then to the PSE pump and dashpot, I had a better understanding of how the system works. One thing EPC doesn’t show is the connection from the PSE pump to the distributor and then to the dashpot. That was a missing link that I was only able to find by tracing the lines.

I still don’t know if my vents operate the way they should. I get the feeling they are working properly based upon someone else’s post about similar concerns. I think MB may have incorrectly documented how the vents operate when selecting the climate control button air passage directions. Even if they don’t work properly right now, I’m not about to take the entire dash apart to replace one or two flap actuators. That would be time consuming. I read it takes about 20 hours just to get access to the actuators. Maybe down the road if a number of actuators fail, I may attempt it.

Here's some summary information on the PSE pump:

Ports:
Port SRU (Manifold Vacuum assist) - Helps with air vent flap actuation when the car engine is not running.
Port BFT/FOND - locks for: Passenger front door, passenger rear door, driver rear door, station wagon hatch
Port FT - lock for driver's front door
Port TANK - lock for fuel tank lid
Port MKL - Not sure. Maybe lumbar seat option
Port Heck/KAF - Not sure. Maybe rear trunk for sedans

vacuum @ 8-10psi locks the doors and fuel lid
pressure @ 8-10psi unlocks the doors and fuel lid

The vacuum/pressure for the doors and lid do not need to be constant. They only need to reach 8-10psi for a few moments for the actuator to change state.

For the SRU (Manifold Vacuum assist) port, vacuum is only applied to that line and it must maintain a constant vacuum. It needs to be around 17psi. If it falls below 13psi, the PSE pump will kick in until it reaches about 17-18 psi. When the car engine is running, the intake manifold vacuum assist port provides the vacuum at a constant rate of about 17psi.

I don't exactly recall the measurement for the vent flap actuator lines, but I think it is somewhere between 10-12 psi of vacuum at a constant rate to remain open. I think below 10psi, the actuators close.
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Last edited by todd_raleigh; 06-24-2013 at 07:30 AM.
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Old 06-24-2013, 08:54 AM   #5 (permalink)
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Excellent information, Todd, thanks!

Consider this a "second" to the nomination for Stickies from Eagleone.

Side note: I haven't seen the term "dashpot" used for years; the last time I saw a dashpot was when working on a carbureted car (as virtually all were then) back in the 70s. In that capacity they were used to keep the butterfly from slamming closed when someone abruptly removed their foot from the gas pedal; rather, the throttle mechanism would hit the post on the dashpot, which would catch it and more slowly let the butterfly return to idle. This process avoided some issues where the engine would simply die if the butterfly slammed closed under certain circumstances.

Second side note: If I had to guess why MB would choose to link PSE vacuum to the actuator circuit, I'd imagine it's so the flaps can be actuated (and air directed) when the engine is off, perhaps in concert with the use of the REST function.

Thanks again!
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Old 06-24-2013, 09:38 AM   #6 (permalink)
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Even with those models passing 17 years they still can surprise owners.
Judging from "vacuum assist" the PSE pump can act as backup for manifold vacuum in times when you use rec mode, or on start up.
My diesel has big vacuum pump mounted on the engine, so I doubt it has the connection, but then, if it works fine, I am not going to dig there.
Thanks for sharing.
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Old 07-21-2013, 03:56 PM   #7 (permalink)
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Hello all. I am trying to locate the PSE pump. I have an issue with my doors not locking with remote nor with switch in dash. Also my trunk will not pop with the remote nor the switch in dash. My rear head rests will not lay down with the switch in dash. How do I reach the PSE pump in a 1998 CLK 320 Mercedes? I see everything saying that it is under the rear seats. How do I get under the rear seats to access it? Thanks in advance for any help that any of you can give.
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Old 08-18-2013, 06:46 AM   #8 (permalink)
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Quote:
Originally Posted by MR12PLAY View Post
Hello all. I am trying to locate the PSE pump. I have an issue with my doors not locking with remote nor with switch in dash. Also my trunk will not pop with the remote nor the switch in dash. My rear head rests will not lay down with the switch in dash. How do I reach the PSE pump in a 1998 CLK 320 Mercedes? I see everything saying that it is under the rear seats. How do I get under the rear seats to access it? Thanks in advance for any help that any of you can give.
If it's like my '00 E430 you locate the two recesses in the seat near the bottom of the cushion on either side. There are levers inside these recesses that you lift up and that side of the seat will be free. Lift it up until it is free from its catch and then release the other side. From that point slide the whole seat cushion forward toward the front of the car and it will be come out. The PSE pump is on the passenger side under that black plastic sheet and is encased in foam rubber.
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Old 08-18-2013, 06:52 AM   #9 (permalink)
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Todd-
With all this routing information now laid out what is the next step. Is your guess that there is a hose leak. From your experience it sounds like the most likely scenario. Unfortunately it also sounds like it could be near the actuator which as you pointed out it more than I want to tackle at this point.
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Old 10-19-2013, 05:13 AM   #10 (permalink)
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PSE Question

Hi Todd and everyone - Mark here in Atlanta. Great thread, but still puzzled. My latest project is a '99 E320 Wagon (non 4M) with 222k miles. Well cared for and runs very well. I've sorted through most of the gremlins so far (windows and seats inop) but still cannot lock/unlock doors. I believe the pump is bad and have got a used PSE pump on the way (part 210800 1348 - not the latest for the wagons, but will hopefully work).

Question related to the pump - does it interact with the interior lights, or any other electrical components, in any way? Opening/closing doors do not turn the lights (all overhead and puddle lights) on or off. To recap what I've noticed:
* No interior lights come on when doors opened/closed (including rear hatch)
* the main light overhead (near sunroof switch) DOES come on when remote unlock is clicked, and fades to off when door is closed or lock button on key is clicked
* the alarm does not appear to be arming
* door locks not working (via remote nor dash switch)
* all door pin switches appear OK

Appreciate any and all information!

Last edited by Roswellmark; 10-19-2013 at 07:28 AM.
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