I had an '87 300D that used to turn on the fan when I washed the engine, but it would dry out and work fine later.

New switch installed, aux fan is now acting normal.
BUT- still can't get the A/C compressor clutch to turn on. I jumped the low pressure switch at the dryer to see if I can fool it to turn on just to make sure electrically the thing works -- nothing. Fuses are are good, including the long strip one by the inner fire wall.
Any other ideas???

FYI my tach works good and I already tried a klima relay too.

What do you mean by tried the Klina relay? Look for a Klima relay pin diagram then send power directly to the compressor. For kicks, replace the Klima relay with a generic relay just to test.

Sixto
83 300SD

I already have an extra klima relay and replaced it, no change.
I jumped pin 5 & 7 in the klima socket- the compressor clutch comes on and the compressor turns freely.
So now where do I go??
And thanks for the replies!

Then one of the Klima inputs is flaky. Do you get an AC (as in alternating current) signal from the compressor rpm sender? Fit an ice cube relay until you figure it out... or don't :)

Sixto
83 300SD

Thanks for the clues!
I hope I can figure it out and fix it without having to add the ice cube relay and switch - trying to keep it original.

Well I have spent some time around the good old " 12-pole connector" for the klima realy.
I think I messed up a test procedure- in the repair manual it mentions setting a meter to (V ~ )
Is this a symbol for AC and not DC current?

So I tried 2 "know good" klima relays and 2 push buttons.
Then did every voltage, alternating current, ohoms and RPM tests in the book.
Did some deeper digging, removed the connector for the evaporator sensor. I was not sure what way the 2 pin thing worked so if its bad I just unplugged it. Nope, still no A/C clutch. I jumped it, still no good.
Now I'm getting real worried that something rotten may be going on with the EDS - electronic diesel computer.
I take a shot and buy a new Klima relay... It WORKS!