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  #16  
Old 12-09-2007, 05:55 PM
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And...they shut off when I pull the relay

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  #17  
Old 12-09-2007, 06:03 PM
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The single wire temp sensor is the sender for the dash gauge only..it has nothing to do with the fan circuits.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU28W12KSLW&year=1992&make=MB&model=500-E-001&category=P&part=Water+Temperature+Sender


the blu , 2 wire sensor is for high fan circuit cut-in @ 105C.
You said you have replaced that sensor???


I would suggest you also do this simple test.
On the drier , there are two sensors . One with spade connectors and the other with a 6" wire pigtail.
The pigtail one is for Low fan circuit, so to be sure we are on the same page, you want to slide the wire covers back on the end of the pigtail and jumper those two wires with key ON and see if you have LOW Fan..
Compare that speed to what you see as High fan so we are sure we are diagnosing the correct circuit..
The FANS have two different circuits..a HIGH speed circuit that is triggered by the engine coolant temp sensor [ 2 wire/blu] and LOW fan that is triggered by the a/c systems high side pressure sw at the drier [ pigtail wire sensor] These are completely different circuits , even though they use the same fan motors...

Last edited by Arthur Dalton; 12-09-2007 at 06:52 PM.
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  #18  
Old 12-09-2007, 06:54 PM
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Will do, but forgive my ignorance; where is the drier and what does it look like?
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  #19  
Old 12-09-2007, 06:59 PM
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I believe on that chassis it should be around the front/drivers side , behind the headlamp..
It is a cylindrical can in the refrigerant line near the condenser [ condenser is the coils in front of radiator, behind the aux fans]
It will have the two sensors I mentioned , plus a little glass window on top
[ refrigerant eyesight glass]...if you can not find it , post again... but just look around in front and you will see it.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU28W14RKXF&year=1992&make=MB&model=500-E-001&category=R&part=A%2FC+Receiver+Drier
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  #20  
Old 12-09-2007, 07:04 PM
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yep, a little fishing around and I found it..jumped and the fans went on, as far as I can tell, not as loud as when engine is running, so perhaps this is the low setting...
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  #21  
Old 12-09-2007, 07:08 PM
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Arthur, I appreciate all the help, I've got to run out for an hour or so, I'll check back in.

Thanks!
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  #22  
Old 12-09-2007, 07:10 PM
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Quote:
Originally Posted by rjfjr1 View Post
yep, a little fishing around and I found it..jumped and the fans went on, as far as I can tell, not as loud as when engine is running, so perhaps this is the low setting...
Very Good.
That would be LOW fan and would be correct. I just had to know for sure that we had the correct circuit and that tells us we are OK.
So, we are back to the high fan circuit and from what you tell me , it looks like you have a bad or inaccurate blu 2 wire sesnor OR a poor connection at the terminals.
Do this test when you get back..

Key ON , car engine temp cool.......remove two wire sensor connector and see if high fan comes On by default...
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  #23  
Old 12-09-2007, 07:13 PM
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I'll do that. Two pin blue sensor (in your first picture) was the first thing I replaced, as well as the connector.
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  #24  
Old 12-09-2007, 08:20 PM
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Removed the two wire sensor, fans did not come on. Jumped together, fan comes on high. Car is not completely cold, if I'm reading my ohmmeter correctly, sensor is sending about 4K ohms.

So, jumping wires at drier turns fans on low; jumping wires at sensor, fan turns on high.
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  #25  
Old 12-10-2007, 10:42 AM
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Ok
I see you have an ohm meter, so...

Get a reading across blu sensor at normal running coolant temp.
Also get a reading on the single wire sensor [ temp gauge sender] to check the gauge reading accuracy.

Here is that comparison between the sensor and the gauge reading

OHM 110 = 60C
67 = 80C
38 = 100C

I have a 38 ohm resistor made up on a plug /harness in my tool box to check the gauge ..by just subbing the 38 ohms for the sender , the gauge should read 100C. Or use one of the other values from the chart.

Also, do you have a resistor bridging the connector to the blu sensor ??? Many guys do this to lower the cut-in temp of that sensor for high fan, but that will not allow default fuction test to be used as ACC panel will still see R value of that resistor even when the connector is unplugged from the sensor.

Last edited by Arthur Dalton; 12-10-2007 at 11:04 AM.
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  #26  
Old 12-10-2007, 11:26 AM
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OK, I'll look into (work intervenes) and will post results as soon as I can.
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  #27  
Old 12-10-2007, 11:31 AM
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Quote:
Originally Posted by rjfjr1 View Post
OK, I'll look into (work intervenes) and will post results as soon as I can.
The time change makes it hard too...but no hurry...
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  #28  
Old 12-10-2007, 11:44 PM
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am I reading this right?

cold - I read 4k ohms
normal operating temp - I read 1k ohms, at both sensors.

I'll get a more sensitive meter, perhaps digital, this weekend. This is a pretty basic one with not much discernible beyone 1k increments.
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  #29  
Old 12-10-2007, 11:47 PM
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"Also, do you have a resistor bridging the connector to the blu sensor ??? "

Nope.
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  #30  
Old 12-15-2007, 07:42 PM
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OK, got the digital multimeter; here are some readings

Running Temp: reading at blue dual pin fan sensor is 430; reading at temp. sensor is 50

AC/Off

After car has cooled somewhat, turn on and idle as temp comes up; fans off to start; Fans Turns on high at: 510 at fan sensor (dual pin); 59 at temp sensor (single pin).

AC/On
Fans come on, low at reading of 65 at the temp. sensor.

Does it seem to you that fans are kicking in at the right points? What's also going on is the mechanical fan is really never engaging. Radiator is actually cool to the touch. With fans going on high, they must be keeping the radiator and engine cool enough to keep the viscous coupling from engaging.

Thoughts?

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