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Discussion Starter #1 (Edited)
PSE - Removal, Refit and Check and Turn over as required

The PSE(A-37) has a vacumn pump to operate the door, boot and petrol filler locks.
It also controls the alarm (if fitted) and the interior light timer, door unlock crash sensor
Plus rear demister relay and ARA control model if fitted.
It comunicates with the DAS thru the CAN from the MFC unit.

I just took mine out to check for moisture. I sprayed laquer over pcb and drilled a couple of 1.5mm holes in base as it can hold water there if it should get in. Water can overflow from blocked drains or faulty rubber boot edge seal.
(Also see post No 7 where I turned unit over ;))

1. remove floor liner
2. remove spare wheel (if fitted)
3. remove jack and holder (pullup at rear)
4. pull out foam box from bottom and remove by folding top back
5. unclip vac pipes (I marked to ident. This is important)
6. unclip 2 wiring loom plugs
7. using a small flat screwdriver to push detents remove base by lifting it as you go around.
8. remove small torx screws (3)
9. let unit drop into your hand
10. inspect for water damage or corrosion (mine was OK)
11. clean if required using nylon toothbrush.
12. spray on coating to seal pcb ( I also sprayed wd40 into connectors)
13. put unit back into housing. Ensure vac tubes line up with top holes
14. replace torx
15. ensure motor stand offs are alighned with base holes and refit base plate
16. refit cable connectors
refit vac lines
17. slip into foam box NOTE: some people have wrapped a plastic bag around whole lot here. I choose not to as moisture "may" get trapped in bag?
18. manouver foam box back into its recess (bugger of a job, mine tore
19. replace jack holder and jack
20 replace wheel or box if fitted
21. replace floor covering and run hand along top of rear edge to reseat under lip.

Good luck

Bazzle
 

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The coating you use to seal pcb(?), is this some kind of Conformal coating? Conformal coating is some kind of silicon that covers the electric right? So that moisture can't get near it? I will do this my own as soon as possible.
 

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Discussion Starter #7 (Edited)
Turning PSE upside down to reduce water damage.

You can trun your early PSE unit upside down like the later models. NO wiring loom req even though MB sells one?
Just need to lengthen VAC lines (yellow) 300mm (1 foot)
I used 6mm nylon pneumatic hose. The yellow line just pushes into it, (spit on it 1st and wiggle in about 1/2" or so.
Foam box fits on after unit held back in place.
Mark which hole you unplugged each line from before removal and cutting.
Not sure re post 2000 as loom is slightly diff due to no rear fuse box??

Bazzle
 

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Great job Bazzle. Did you remember to use a soldering iron to burn some holes in the bottom of the foam coffin so the drain holes you put in the PSE housing have a place to drain through?

I did this about two years ago and have never had a problem with it.
 

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Discussion Starter #9 (Edited)
n5160u said:
Great job Bazzle. Did you remember to use a soldering iron to burn some holes in the bottom of the foam coffin so the drain holes you put in the PSE housing have a place to drain through?

I did this about two years ago and have never had a problem with it.

Cant remember.

Next time I am going to extend Vac lines with plastic tubing and try to turn unit over.
Done see post 7 above

Bazzle
 

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Bazel: I have been checking up in local stores what it awayable when it comes to the conformal coating. I have found two different types, and want to check with you what kind you used so I don't make a mistake :)

1, a spray that will keep the parts from rust/moisture, and cleans the circuits, but is not hardened.
2, the same thing, only that when this dries it gets getting hard and like a film/coating lying over the board. That will protect against water/moisture forever.

I think number two is the one that is sounds best to use? Or is there any issues related to cover the board?

Question is, soft or hard.
 

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Got my car back from the dealership today after a PSE pump fix. I looked at the pump and apparently part of the fix now is to wrap the pump in a clear bag. I know this was discussed on other threads and it was stated that this could cause condensation to build up, but I guess MB doesn't care.

Should I go ahead and put a small hole in the bottom of the sealed bag or not?

I tried to pull out the unit to inspect the wiring and make sure they had performed the loop addition with a longer harness, but the bag was sealed and I didn't want to mess with newly completed work. According to the service print-out they did perform this harness extension/swap, but not sure what good that will do if the bottom "drain" holes on the pump are running right into a sealed bag. :rolleyes:
 

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If all the wires and hoses exit at the bottom of the bag you will be OK. The water that gets into the car will run down the cables and hoses and if the cables extend below the bag and turn up towards it, than the lowest point is the wires and hoses and the water will drip off from the lowest point where it loops back up as opposed to the original version where the hoses entered the pump from the top and allowed the water to fill the pump housing.
 

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After fresh thinking I put mine in a new plastic bag that I stuffed all the way into the hole where the cables/vacuum hose come from. Think this will stop the issue about water running down the cables, since the pump is higher than the hole. Will use it for a while and see.
 

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n5160u said:
If all the wires and hoses exit at the bottom of the bag you will be OK.
From what I can see, the entire pump and foam shield are covered, and the only opening is with wiring at the very top of the unit, which has tape/adhesive sealing the bag around the wiring bundle.

The TSB has them add the loop in wiring that allows for the "lowest point" drip that you mention, but it appears that if this loop does now exist, it's inside the sealed bag (which does me no good). I'll have to take a closer look at this mess when I get the chance, but as I mentioned in the above post what I don't want to happen is the removal of the unit to result in me screwing up the sealant fix Mercedes has just performed (even if it's relying on a sealed bag to keep the unit dry).
 

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My understanding of the fix was to lengthen the lines so the unit could be mounted upside-down. That way the wires and pnuematic lines are coming out below the pump, and the circuit board is at the highest point. If they lengthened the lines but mounted the pump in the same orientation as it was, I think they did it wrong. As I recall, someone with a newer SLK (2004 maybe) checked and his came from the factory with the pump in the upside-down position.
 
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