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Old 04-26-2001, 01:28 PM
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I have a 1995 C280 witht the master vaccum pump cylcing on and off and there's a leak in the vaccum lines behind the dash - this is what a MB dealer diagnostic test said. Anyhow, once I pull that dash out, how can I find the leaky lines - do I use a stethoscope or blow smoke in lines or use vaccuum line tester. Also, where can I get the testing quipment that I will need. I would appreciate if someone could tel me the cheapest, most economical way to find the leak.

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Old 05-03-2001, 08:13 PM
MBenzNL's Avatar
Join Date: Jan 2001
Location: the Netherlands
Posts: 1,417 replies...

Hello Troy,

To determine whether it is your vacuum lock system or heater system that is leaking, you should just listen to the pump after you lock the car. If I am correct, the pump has got two separate systems for the locking and heating. If the pump does not run long at all after you lock it up, you have a leak in the heater system (but I think that the MB tech knew what he was looking at when he diagnosed the car).
I have no experience with a stethoscope and hate to blow smoke in the vacuum system, so I would either go for my ear or for a vacuum tester to determine where the leak is situated. If your pump is humming for a longer time period, you should be able to hear the hissing sound where the vacuum line is leaking. That is exactly the reason why you should keep the climate control panel connected to the plugs after you removed the dash (your SRS light will illuminate after you are finished, but that is no problem). I think the leak will be heard after the dash is removed (the pump pumps quiet a lot of air when it is running).
The vacuum lines to and for the heater system are not yellow (yellow vacuum lines are for the central locking) but you will find some lines of different colors (green, red, clear). I have attached a picture with some vacuum lines on the heater system...

Let me know how you are getting along!

1990 300SL-24
1993 C250D
with a minor 600+k kilometer
(the Netherlands)
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