I am the second owner of a 92 300DT. Beautiful car. This forum has been very helpful. Car has had gentle use, belonged to an elderly librarian at my old middle school. Car has had Dealership maintenance ( poor) since new. Oil changes etc every 5k miles since new. Ac compressor works, puts out nice cold air, but wont kick in and out by itself. Ran a jump wire to the battery to make sure it was functional. It just doesn't kick in on its own. Suggestions? Ideas? Solutions? Any help would be appreciated.

Tachometer working?
If not I'd suspect the cop realty.
Otherwise it could be a faulty pressure sensor or more

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97 e300d, 78 300Dt, 95 E300d, 94 E320 estate

Head on over to http://w124-zone.com/downloads/MB%20CD/W124/Main.html
and look at Chapter 83

Everything you need to know to troubleshoot the system is there.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech