Found that the Aux. fan was broken on my 81 240D, so I went ahead and replaced it with a new one. Had a few question about when does it turn on..

1. Does the aux. fan turn on when the engine temp. is at 100c?
2. Does it run when you turn on the AC?

When I turn the AC on, the aux. fan doesn't start nor will it go on at 100c.

The fan is activated when the a/c refrigerant temperature reaches around 120 degrees F. Or the engine compartment temp gets hot enough to trip the switch.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Mine comes on when the temperature switch on the AC receiver-drier gets to 52C or 126F, or the engine compartment reaches that temperature.
There's an aux-fan relay over on the left inner-fender and the relay coil takes power off of fuse #12 or the AC relay.
The aux-fan power circuit comes off fuse # C.
My wiring diagram shows no aux-fan temperature switch on the engine.

Happy Motoring, Mark

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DrDKW

Ok, will give it a try with running the A/C and see if I can trip the switch for the fan. It is very hot today so I should have no problem with reaching 120F.

There is a temp. switch in the engine block, and there is a black wire that connects to the switch. I replaced that also because it was broken. Which of the relays in the box controls that fan? I have two relays in the box..

Did that cause your temperature gauge to start working normally?

One relay is for the fan, the other is for the compressor clutch.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

According to my wiring diagram, the aux-fan relay has a fat yellow wire from the aux-fan motor connected to terminal 87, and a fat red & black power wire from fuse C connected to terminal 30. There should be a little diagram right on the relay showing the terminal circuits & numbers.

Happy Motoring, Mark

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DrDKW

i've never found this thing to work correctly. i installed a manual override switch that controls the fan from inside the cabin.

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1981 NA 300D 310k miles

FWIW, I resuscitated my aux fan by custom-forming the motor brushes from ones readily available in a Sears parts department. Bit of cutting and shaping with Ye Olde Dremel was all it took.

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'83 300 SD
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

That's frequently a side effect of low refrigerant. Never gets hot enough to trip the switch.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I guess the engine never got hot enough yesterday. I was thinking that the refrigerant was low, as the AC hasn't been used in a long time. I was going to convert it using the AC-PRO conversion kit but I think that they don't sale in in California, as I haven't been able to find it in any stores. I only find the refill cans...

Check out:
http://www.peachparts.com/shopforum/diesel-discussion/356684-f-s-accessory-c-compressor-clutch-condenser-fan-run-together.html

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All Diesel Fleet
1985 R107 300SLD TURBODIESEL
2005 E320 CDI (daily)

LOTS of parts for sale!


EGR block kit
http://www.peachparts.com/shopforum/diesel-discussion/355250-sale-egr-delete-block-off-plate-kit.html

1985 CA emissions 617 owners- You Need This!
Sanden style A/C Compressor Mounting Kit for your 616/ 617 For Sale + Install Inst.

Sanden Instalation Guide (post 11):
http://www.peachparts.com/shopforum/diesel-discussion/367883-sanden-retrofit-installation-guide.html