I usually post on the diesel forum but I am having what I believe to be engine speed sensor problems on my 87 300D so I thought I'd post on this tech forum. What seems to be happening is when the underside of the car gets wet, the air conditioning compressor quits and the tachometer also quits. They won't work again till everything dries out, maybe 45 min to 1 hr. Even shutting down and restarting won't bring them back up.
I have read briefly about the Klima relay, but I am suspecting the engine speed sensor because I can't really see the Kima getting wet where it is located.
My question is, does the engine speed sensor also send the signal to the tach? Or vice versa? I am thinking if there is a failure in the speed sensing circuit that there would be no signal for the compressor sensor to compare, keeping the compressor circuit open.
Also, how exactly do I get at the engine speed sensor? Is it underneath the car?
Is there another sensor or relay I should be looking at, given the facts? I think that the fact that the tach and the compressor both go out at the same time would be a pretty good clue for someone more experienced in this system than myself and I would sure appreciate any help.
By the way, I also considered that when the car gets wet the belt probably slips which could also probably trigger the sensors to cut power to the A/C from the difference in compressor vs engine speed, but if this were the case, wouldn't the cutout reset after shutting down, rather than having to wait 45 min to 1 hr? And why would the tach also fail?
Thank's in advance for any and all help.......Brian in HOT Arizona.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

The crank sensor is located on the bellhousing and reads the flywheel. The signal is carried by the circuit to the EGR transducer which converts the inducted AC signal into a pulsed DC signal. That engine speed signal is then used by all that need it, including the AC, the idle stabilization system, the tach and probably the ABS.

The OVP powers the EGR transducer if I recall and thus can kill the signal.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks Steve I'll just have to test the sensors and relays as per the manual. Trouble is, it's not so easy when it is intermittent. I guess first I should look to see what can get wet.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K