w124 230TE Aux Fan not Cutting In

Hi there,

My 230TE overheated the oher day (lots of steam - and yes I am aware the antifreeze level needs checking!) and today I finally got round to checking the reason. This is proving harder than I thought - I've checked the forums and cannot find anything similar given what I have checked/done so far.

Thermostat is OK. Tested it and checked the radiator heats up and the heater heats up. Engine temp around 80C during normal motoring, which I understand is what it should be. Temperature rises only when stationary and fan does not cut in.

So, if fan does not cut in must be the switch (its gone before). But I've tested the fan switch (two prong - electromagnetic fan, no aircon) and this is fine going open circuit at about 100C. I've also bridged the twin socket connector for the fan switch, which should have caused it to roar into life - alas it did not! I have checked for, and found, feed voltage at the connector to the fan switch on the engine.

Fuse D and Fuse 7 are OK.

SO - am I right in thinking there must be a problem somewhere after the fan switch on the engine? Possibly with the wiring (she is getting old bless her!) or with the electomagnetic clutch itself?

If anyone has any other ideas please let me know!

 

Is your engine fan a visco or the electric clutch type

 

Thanks for replying Television!

As far as I know it is electric, the fan switch (red top two prongs) operates at about 100C - I think it would be about 85C if it was viscous. The fan spins fairly freely when the ignition is off and there is no obvious resistance from a viscous coupling. When I last noticed it cut-in the fan came in with an audible click at around 100C on the temp gauge.

Engine type is M102 and the vehicle is 1990, which I think was before viscous. So all in all I'm pretty certain its electromagnetic.

 

This is the rad fan circuit mainly intended for the air con

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1989/300CE/SYSTEM WIRING DIAGRAMS/3231.pdf

Re this engine fan again, there are two thin wires running up the front of the engine at the rear of the engine fan, one goes to the thermal switch on the front of the engine and grounds that wire when at 100c so if the other wire has 12volts on it and the thermal switch grounds correctly if the fan does not work, then the clutch winding is open ciruit

 

you have to verify earth at the fan electromagnet as well as power - checking the continuity to ground at the fan side of the thermoswitch is a good way, expect maybe 2 or 4 ohms.

 

The OP has tested and shorted out the thermo switch top front of engine

 

Tried putting power across the fan itself to check that still works?

When you say 'aux fan' do you mean for a/c?

cheers

 

Hi again - thanks for all these useful replies.

There is no air-conditioning. The fan is the single fan enclosed by a shroud that pulls air through the radiator to cool the engine. On the circuit diagram I have from the Brooklands manual the fan (labelled Y2) is called the "Electro-magnetic clutch engine ventilator" and earths directly at point W11, which should be the engine.

I cannot find the equivalent diagram on the Russian site - the one suggested is not for my vehicle I'm afraid.

I will try to trace the wires to the back of the fan and check for continuity and also check the resistance.

 

There is an easy way to test, you need a volt meter, just pull the connector off the thermo switch and that goes to the fan should have 12volts on it, a further test is that this wire should also light a small bulb

 

Which was not what I had said, I had read that post.

These have a switched live supply through the thermoswitch, this then goes through electromagnet to ground.
As we have power through switch and switch is not at fault (as proved by bridging it), we now have to verify the continuity through the electromagnet to ground, as per my suggestion.

 

There is 12V at the connector to the thermo switch as per my OP - sorry if I did not make this clearer.

Alex - would I be right in thinking that I should get continuity through the other connector (NOT the 12V feed) on the thermo switch to say the engine block or another convenient earth?

However, I did shove 12V down that connector from the battery and the fan did not start.

I strongly suspect that the wire to the fan body is broken somewhere (or the connector has been pulled/fallen off!!) or the windings in the electro-magnet are open circuit as Television suggested.

I'll try and get to the connector at the back of the fan and run a 12V feed to it - if the fan works (can I use a courgette instead of a carrot? ) then it is the wiring at fault (no trouble to run a new bit of wiring from the thermo switch I hope). If not it must be the windings - and a search for a replacement fan unit.

Thanks for helping...

 

Carrot trick is really for viscous clutch - if the electric fan is working ok it will spin up quite noticeably (think helicopter...) with the hood up...no need for carrots

Did you try 12V across the fan to check it?

cheers

 

OK so I had it the wrong way round, so yes if the fan has a grounded wire then the thermo switch provides the ,live,,

As the fan does not run with the switch shorted the fan open circuit somewhere, this reminds me of a very old post here where the wire had broken just under where the fan is bolted on, a new wire and all sleeved and it was fine

 

I did try 12V across the fan - nothing happened. I was a bit cautious with this test (I am not happy when large whizzy things might start up when I'm leaning over the engine bay. I'll re-test this tomorrow, when the rain stops!

 

Update

I thought I'd posted a reply about the final fix to this (but obviosly have not!). Anyway here goes, it was the windings of the electromagnet. £30 part from local scrappy fitted by my local independent did the trick (it did not stop raining!)

 

Thanks for posting back and pleased its all just fine