Peter ..how is changing brake pads at all related to the topic of this post

I've encountered this phenomenon a few times in my 190E, too, but I haven't a clue what it is. The ticking interval is about one to two seconds and it sounds like it's coming from behind the RH dash or maybe the RH kick panel.

I'm also not sure what the "monovalve" is. I am familiar with the vacuum operated heater flow control valve and the AC expansion valve, but not the "monovalve". What is it?

The ticking sounds like it could be some kind of mechanical relay.

Duke

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.

Dave

__________________
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

Mafioso: It was simply a mistake I made. I still would like an answer to my qustion. As a Doctor, I hope, as does my insurance company that these are the only types of mistakes I make. Sorry

Peter....it's ok man.....no need for any appologies....