1987 260E electric fan in front of condenser
 

car: 1987 260E M103 2.6L

Hello, I notice there is a large electric fan located just right in front of the condenser. The condenser is the radiator like heat exchanger that sits right in front of the radiator. It never seems to be on. I wonder what it's for? Is there a way I can hot wire it so it will turn on when I need it to cool the radiator? I hope to do this while I wait for a replacement fan clutch to come in.

Sure, you could do that. Easiest would be to locate the relay (there should be a high and low speed relay in the back of the fusebox, I believe).
The low speed relay is normally triggered by the AC high pressure switch, the high speed relay is triggered by an engine temperature switch, so the fan runs in low speed if the AC pressure gets too high, and the high speed will come on only if the engine is getting very hot, usually it's on over 200 degrees or so. If you wanted high speed fan on a switch, you might also get this by messing with the temp sensor wiring, not sure if it woudl affect anthing else or not, can't think of anything, maybe the gauge, but that might be a seperate sensor.

If your cooling system is working correctly, there would be no need for any additional cooling.

Mercedes has already done that for you. As Gilly said, the fan is controlled by both the high pressure switch on the receiver/drier when your A/C is running, and by a coolant temp sensor all the time. If those two components are working properly, and if your A/C system is properly charged, and if the aux fan circuit is good (relays, fuses, series resistor, wiring, and fan motor), there's no need to devise a work-around. Why not just fix the underlying problem rather than trying to "trick" the system. Especially since the aux fan circuit is particularly easy to troubleshoot.

It's not. That's why I need this temporary solution. Right now the fan clutch is shot, so the engine temperature gets hot while driving in the city with lots of stop & go traffic.

got to get a fan clutch....... even keeping the aux fan running all the time is going to cause you trouble in stop and go... you will find yourself having to hit the defrost button the give the engine heat relief.. i think i just got my new fan clutch for 55 dollars on ebay...

make sure your radiator cap is tight and the box is holding pressure... five dollar helper

Actually I just ordered a new fan clutch from Ebay too. Waiting for it to arrive, probably a week or two. Just trying to mitigate the situation in the mean time as I need to drive the car.

May be pretty cude, but if you disconnect (I believe) the correct plug on the temp sensor I think it'll put the fan into high speed. Won't wreck anything by trying. It is between the valve cover and air cleaner, screwed into the top of the head. There are a couple different ones.
OR you can disconnect both wires from the high pressure switch for the AC, jump them together, and the low speed fan will run. In both cases it should stop running with the key off.
Won't be able to switch it on/off when driving though, but for a few weeks, should be fine.
Gilly

FYI. Don't want to contradict anyone or seem argumentative, but it may not be a good idea to wire the aux fan for continuous operation. The wiring to the fan is undersized for continuous operation, potentially causing the wires to overheat and burn out. For your consideration.

Yeah I know what you mean. I'm just the enabler, he can live with the consequences. Actually low speed might be the way to go. Oh wait won't the fan keep the wires from melting? hah!

high speed is the way to go because you don't want to heat up the ballast resistor and cause it to fail.the plug gilly is refering to is the double pin blue plug----be careful it's brittle.unplug that and full speed fan will be on with ignition.

You did not specify how hot your engine gets but my previous car was a 260E and when it overheated the head warped and the countdown to head gasket breach began.

You might consider raising your water:coolant ratio until the fan clutch is installed -- possibly even running on straight water if you feel it will only be a week or so. It's worth the effort as getting stuck in traffic on just one occasion is all that would be required mess things up pretty badly for you.

manually override the aux fan
 

Throne7,

I'm a major newby here, but I have a W124 (87 300E) with the same problem. I followed Arthur Dalton's instructions on overriding the aux fan while keeping the OEM circuits in place as described here:

http://www.peachparts.com/shopforum/showthread.php?t=254651&highlight=w124+fan+arthur+dalton

I wired this up and it works perfectly. I can manually control the fan whenever I want. Works great.