On my 85 300TD Wagon I was having a problem with an intermitten tach and the AC was not very good then the tach stopped completely. And the AC also stopped being cold.

I checked the compressor and it wasn't engaged. I came to the forum & started running the checks it recomened. In the end I jumped across two legs of the Kilma, and the compressor engaged and the air was cold. But the tach didn't work. I checked the OVP relay and the fuse was good. So I changed it with a friends OVP and WOW the tach worked. So I took the jumper off the Kilma and tried the AC & WOW it worked also......

It was a bad OVP relay all the time.
Maybe this short article will help someone else.

Phil

__________________
Phillip Babcock
Ft Myers Beach, Florida

2005 E-320 CDI Desert Silver
2005 E-320 CDI White
1992 300D 2.5 Turbo 2 tank WVO system - selling
1984 300TD Wagon 2 tank WVO system Sold

Good fix Phil, and nice of you to post.
Took me almost 3 years to fix the tach on my '85. It was quite a bit more involved though.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

This was the exact same experience I had with my 1995 E300 Diesel. Put in a new OVP relay and tach and a/c work beautifully.

__________________

what year did MB start putting this OVP rel;ay in the vehicles.
and where is it located??

I believe they began (in the E-class and predecessors) with the 1985 300D (W123), in which the OVP relay is behind the right front passenger kick panel, just below the glove box right side (near the right front door upper hinge).

In the 1987 300D (W124) the OVP is with some other electronics, in the compartment behind the battery.

The W210 models (1996 – ?) have a "K40" relay that does the same function, and a bit more. In is in an instrument case under the hood, on the right side, behind the air filter.

The OVP may have originated (first use about 1984-85) with the W201 (190, C-class) cars but that is only a guess on my part. Don't know about OVP use in S-class.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Does anyone know if the OVP from W124's is a direct drop in replacement for my 1985 W123?

I am having the same issue as the OP.

sounds like it may be time for a junkyard run...

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

No.

BUT,

See below:

Attached Thumbnails

   

__________________
'84 300SD sold
124.128

OK, so i need the OVP out of an '85.

I don't understand the significance of the picture. I now know what it looks like though so I can go grab one. This is right on the borderline of just getting one from a parts counter.

dd

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car