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Old 12-14-2003, 12:59 PM
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dmorrison dmorrison is offline
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Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
The mono valve is usually located in the engine compartment. Check your service manual for the location. The sound has occured in some of the Mercedes I have owned. I have always figured it is the vacuum actuators for the Ac system bleeding the vacuum down slowly. It may make this ticking sound as it bleeds off.

1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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