Can anybody here identify which of these relays provides the feed for the dual auxillary fans on My 1989 W124 260e? Car is RHD Japanese version.
here is a foto of the relay box located behind the fuse panel from underneath the bonnet. My auxillary Fan is No Go neither with over heat or if the AC is turned on. Tanks in advance Non of the relays has the obligatory fuse on the top. (Cruise control doesn't work either)

My auxiliary fan was not working and it was due to the Resistor that is forward on the drivers side of the engine compartement on my 1988 300E. Sadly they replaced the fuse and just coincidentally the Fan froze up.

I would check your fan to make sure that it is not froze up.

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1999 Mercedes ML320
2002 Mercedes 230K

The relays have position markers under them. The high fan relay is in position "B"
Low fan is "C"
There will be the square relays on the left in pic.

The fuses are #7 for relay coils and fuse D for Power.

A quick test for fan circuits:
Key ON
Pull the connector off the blue coolant sensor at therm. housing..that should get HIGH fan

Jumper pigtail wire harness at a/c drier at end of pigtail. that will give you LOW fan.
Report those findings.

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A Dalton

Nothing happens on this test.
Fans are O.K. - connected battery direct to fan wiring and fans operate. I am checking the power distribution with a multimeter.

OK

I am assuming you tested the fuses I mentioned ???

Behind the headlamp [ don't know which b/c you have RHD], there is aux fan Resistor..the wires burn off,,check that for the next test.

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GO19XIJQ&yearid=1989%40%401989&makeid=MB%40%40MB%40%40X&modelid=260%2DE%2D001%40%40260E&catid=G%40%40Cooling+System&mode=PA&subcatid=G5040@@Aux%2E+Fan+Resistor&source=www.peachparts.com&clientid=catalog.mercedesshop

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A Dalton

Resistor is fine and connections to it a fine.
Checked potentiual to the relay holders - fine in both relays.
Relays work fine. Tested outside car wioth seperate power supply and checked contacts with multimeter.

I assume that the temperature sensor sends a signal to the ECU which in turn operates the relay which supplies 12 volts to the fan on the high speed side. I also assume that the air dryer contact also supplies a signal to the ECU which operates the relay for the low speed
Assumption being the mother of all .....

The local stealerships computers only list the production change variation - and then list a Behr product. The unit I have is a VDO unit - not apparently installed in the Australian versions of the W124 - (mine is a grey Japanese import.)

R12 gas is officially banned in Australia (as in the rest of the "Western world" - still produced and used in many third world places). There are some places where R12 is still available. (I have a line on one of these places). I will see what I can do.

As an aside my car - grey Japanese import should have been converted to R34 as part of its import licensing. (Must have slipped throuigh the radar so to speak)

To order the sensor from Fastlane is unfortunately overly costly from Australia -conversion rates and then expensive postage.

When I recieve the new sensor I will wire and internal switch with 250 ohm resistor in parrallel with it.

Recharge AC
New viscous fan
New blue sensor

My tech's shop uses Freeze 12 if I'm not mistaken . . works well w/ R12 substute.

Don't do that . . unless you want your Aux Fans to run all the time . . . just replace the sensorand see that everything works as it should.

After you're sure all is ok, you can add a resistor across the sensor. Details shown in MENU#18 of the values to use. Most use the "92 C" resistor.

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Regards . . . . JimF
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'94 S500 Cpe

Visit my Mercedes Web Page

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I suspected a possible difference in sensors for Asisan version, but be aware that the 250 ohm resistor as a bridge is not the correct value
you are going to need..what you are going to be looking for is a resistor that drops the TOTAL of the sensor and the resistor to approx 250 ohms. [ cut-in ] That 250 is not the bridge , so you mis-read that. You will know that when you get the new sensor and see what that value actually is.
The reason for the parrallel vs series is a series resistor will increase the total sensors circuit resistance, but a par. circuit of resistor and sensor will DROP the total R , thereby triggering the High Fan on sooner/low temp. Reasoning here is that the Sensors R drops as temp increases..that factor is what allows for the concept of the R bridging. Parrallel R always drop the R factor lower than the smallest R in the group. So, you are dropping the R/T ratio even further, getting a faster cut-in fan .What your final R needed can be calculated when we see what you have to work with new sensor . An est will be around 1200-1400 ohms, so don't go buy any 250 ohm resistor yet.
That info is all in Jims page.
My preference for yor chassis [ IL-6 engine] is to drop the circuit to a point where the fan cut-in is approx 100C , down from the 105/107 they use. That gets you the added jump on temp rise w/o having the fans on too much.
That also gets you a cut-out of a few degrees less. The V8s suffer from running hotter and some guys prefer to trigger the fan earlier, but that is owner call. Where you live/ambients is also a factor ..I find the 6 engine seldom requires a high fan, even when a bridge mod @100C is installed..just the nature of the beast.

You can see why I like the cabin switch..I am the deciding Factor and I am ZERO OHMS ....
It is a good mod . and many have done it..It is also another cheap $$$ improvement, so that makes it even more tempting.
Be interested in the actual sesnor they send for that car..as I for one know little about what they did w/asian exports..
See ya

Jim F
I see we were answering at the same time , so I leave it there........

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A Dalton

I was going to put the 250 ohm resistor in series with the manual switch so that I don't put a dead short across the sensor. I didn't intend on altering the resistance of the sensor at all. Manual switch for emergencies only - after I replace the original sensor.

Meanwhile The red sensor I bought will go into my W190 2.6. This car is a U.K. version. There is no auxiliary sensor at all in this car. The Auxiliary fan only operates off the air con. Maybe the auxiliary fans were not needed in the U.K. due to ambient weather there. - certainly required in Australia - in particular where I live - summer temperatures often above 40 degrees C (over 100 degrees f)

Doing that will also screw up the system . . if you put it in series, the N22 controller will see it as the sensor resistance + 250 ohms. So at 100C when the sensor is supposed to be around 300 ohms, it will "see" 550 ohms and the aux fans won't come on.

You can only put the resistor in parallel with the sensor (ie across the leads) and the 'trick' is to get the correct resistor. Typically the value varies from 1.1K ohms to 1.8K ohms. Depending on the value chosen, you will turn the Aux Fans on early, from 92 - 93C to 98 - 99C.

I personally don't like adding "switches" but some think it's the only way to go since you can control the fans. I'd rather see the 'system' make it's own decision as to when to come on and go off.

Oops . . didn't read what you said . . . You said "manual switch". If your manual switch is basically a "short", it still may not work depending on where you place the switch in relation to the N22 wiring and the value of the resistor + stray resistance in the wiring . So use a 100 ohms to be sure.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

He is talking about the temporary switch until he gets the sensor...........

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A Dalton

bumpy bumpty bump bump goes the bump