Auxiliary electric fan quit - help?

[s class]

The electric blower fan in front of the radiator has quit on my 280SE.  Yesterday I got to investigating, and found that the fan works when given a direct supply from the battery.  The cabling all appears in tact.  The 100 degree switch is good too.  I established that it must be relay controlled, and probably the relay has given in.  But where is the blasted thing?

In my engine bay fues box I have only one relay - for the fuel pump.  Under the driver's side knee roll, there's a row of three.  The rear most one is for the aircon, the front most one for the electric windows.  The middle one, well I can't ascertain what its for, but replacing it didin't help the fan. 

Higher up under the dash are the flasher relay, and another large one in a black plastic box.  What's that for?

Any help appreciated.  Thanks. 

[koan]

The US wiring diagram book (which is not always correct for RHD) shows a single relay code 6 for normal and A/C, and two relays code 6 and 8 for later ACC models. With both types all relays are in the kick panel

Fuse number 2 feeds only the aux fan, is that OK?

Do you have A/C? Does the fan run if the refrigerant temp switch connector is shorted (screwed in top of receiver)?

Hope that helps

koan

[TJ 450]

I would ground out the female connector for the temp sensor to the chassis/engine, because afterall, that exactly what the temp sensor does to complete the circuit. That would give you the definitive answer to where the problem lies. I didn't think there was a relay for the fan.

As for the relays, the  large black one up in the dash I assumed was for the wipers, but I could be wrong. There is also an aluminium one approximately the same size and that's for the rear window heating element.

Tim

[s class]

Ah TJ I think you must be correct.  I opened the black unit and it is a lot more complex than a simple relay - makes sense for the window wipers - controls the imtermittent function and variable speed.  If I ground the wire at the culinder head, nothing happens.  I have traced that wire and it enters a loom going up to the fuse box and then through the firewall.  It ought to have a relay, beacause that wire that goes to the switch ib the head is waaay to thin to carry the current of the fan. 

[Big_Richard]

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[koan]

I would ground out the female connector for the temp sensor to the chassis/engine, because afterall, that exactly what the temp sensor does

I assumed

The 100 degree switch is good too

implied that had been done, suggesting shorting the A/C refrigerant temp switch is the next logical thing.

There is a relay, if a helper can ground the water temp switch while you should feel or hear one of the kick panel relays operating, if not it is the relay or the wiring to the coil.

koan

[s class]

koan, I have ascertained that there are three relays in the kick panel.  The first and last, I've worked out what they are for.  The middle one must be the one for the aux fan.  Replacing it with a known working one made no difference, so sadly it seems to be a wiring issue which is a royal disappointment and a bugger to fix. 

[koan]

If you can find the numbers on the wiring harness to each of the relays that will positively identify them.

I posted a list of relay code numbers some time ago, seach the forum for "relay" or "numbers" in the subject.

koan