I hoping to put an end to the pneumatic issues that I have discovered that 
appear to have plagued this car for years.  I spent a while studying all of the 
records last night, including the complete history from the MB dealership where 
it was purchased and maintained for the first ten years of its life.

It’s had a grand total of four PSE pumps replaced over the years.  Right now, 
the locks work, and the lumbar bladders would work (one is leaking due to age) 
but the back up aids don’t extend.  Fuel mileage is marginal as well, so I’m 
almost positive there’s a vacuum leak in the system, too.

If you’re not familiar with the PSE pump in the 90s models, it provides both 
vacuum and pressure for door locks, AC flaps, lumbar bladders and in the case 
of the W140 from 92-95, these little “antennae” or “sticks” that extend out of 
the tops of the rear fenders when the car is in reverse so you know where the 
corners of the car are.  Mercedes refers to them as “back up aids.”

The PSE works with engine vacuum in the sense that if engine vacuum to the 
system drops below a certain point the PSE will kick in to help out.  This 
allows AC flaps to work when the engine is not running, primarily for the ACC’s 
“REST” function (heat available after the car is shut off.)

There is a vacuum distribution block in the passenger front footwell that is 
prone to leak and often overlooked.  I have a new one on order, as they’re 
cheap, but I’ll be testing this one today as I suspect that’s where the problem 
lies.  The giveaway is the loss of AC flaps when engine vacuum drops due to 
acceleration.  The PSE pump isn’t able to keep up and the vacuum drops, causing 
the flaps to go to the default (defrost) position.

It’s pretty amazing looking back over the records on this car.  I’m thinking 
the independent they used for the last ten years had a big boat, or a kid they 
needed to put through college.

In less than 80,000 miles, the car has had the following replaced:

Power steering pump (2x)
AC compressor (2x)
AC evaporator (2x)
AC condensor (2x)
Ignition lock cylinder (2x)
PSE pump (4x)

It was like clockwork when they would have the car in for service with the 
independent and it would need some sort of major work.


> On Sep 5, 2015, at 10:50 AM, Craig via Mercedes <> wrote:
> I wish you success!
> Craig
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