Hello all! I am new to the wonderful world of MB, and my 1990 300E 3.0 has been doin' some mighty strange things! Car runs great most of the time but lately if the A/C is turned on the air pump engages and somtimes even the ABS pump as well. The engagement is intermittent (on/off/on/off sporadically) and will usually result in the engine dying. Also, the tach jumps up to about 2K while the "clutches" are engaged. Really wreaks havoc on the idle. Now heres the really wierd thing, if I disconnect the high pressure cutout switch while its in its "funk" problem goes away, reconnect it and..VIOLA! its back!

Can anyone of you nice and much more intelligent gents steer me in the right direction, or should I call the GHOSTBUSTERS!

Seriously Stumped

The only think that ties all this together is the Klima relay for the AC compressor (unless there is a different compressor control system in that model) -- the relay gets tach imput, compressor speed input, low, and high pressure switch input, and input from the pushbutton unit and "decides" when to engage the AC compressor clutch.

If it has gone funny, it could be feeding improper signals into such things and the ignition.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I should have posted the results earlier but PSFRED was right on. It seems after the dealer replaced the ECM he didn't get the Klima relay properly seated. Now that it has been installed correctly it works like new!

Thanks for the tip, saved my butt big time!

Warm weather coming exposes one of the Achilles heel of the W124 and W126 and earlier MBs, the airconditioning. (see later post on forum)

Glad to hear you're chillin' like Dillon!

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)