Interesting experience recently. Did some small fiddling with SWMBO's 300E 2.8 while she was overseas. For the last little while (OK, all summer) the a/c would switch to the defrost vents while accelerating, then return to the dash vents when the throttle was closed up a bit.

I knew this meant a vacuum leak had cropped up.

Well, I chased it down to the red w/grey stripe line (it originates where the mess of lines split apart near the brake booster). That's the line to the vacuum reservoir for the climate system.

Checked all the other lines and they are good. Well, the 2nd gear upshift delay seems to be disconnected...how did that happen? Checked all the climate pods. No leaks there.

So I pulled the red w/grey stripe line. Bit of hassle, you have to remove the battery and the inner fender liner - the vacuum reservoir is tucked down in the fender with the coolant overflow tank. The line appeared to have been attacked by acid. Strange, because the damaged section was directly in the center of the car, under the air intake. The section behind the battery was clean. Not much evidence of acid leaking from the battery anywhere. Odd.

So I replaced the center section, leaving both ends red w/grey. I like the color coding of the vacuum system, makes everything easy to diagnose.

Here's the interesting part. Ever since we acquired this car, the transmission has shifted a bit hard. 3-4 could even clunk a bit. It's had some air leaking out the defrost vents - common enough with an older Benz. And the idle. It was perfect with a/c off - couldn't even tell the engine was running. But with a/c on there was a bit of a vibration.

All that stuff is fixed. The transmission is seamless. The idle gets smoother the more I drive it - I guess the engine management software is adapting to the lack of an air leak. And all the a/c now comes out the dash vents.

This thing had a vacuum leak ever since we purchased it. Never would have suspected such, the symptoms were just too subtle. Now all you OCD owners of used Benz automobiles can add checking the entire vacuum system to your list of tasks. Go purchase thee a mightvac. It does make a difference.

Lecture over,

- JimY

very well put and well written it held my interest.did you ever find out if west nile virus or aids responsible for the swiss cheese job on the vac line?seriously though it prob was in the dredded body shop and got beat to death. david poole dallas tx.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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