These fans are driving me nuts. They come on and off whenever they want. On a cold day I will turn the key to the on position and the fans will run. The next day they won't. Sometimes they turn on and off every few seconds then they may stay running. Can' figure it out. Any suggestions I'll appreciate it. Thanks

Check for a good connection at the blue temp sensor on the thermostat housing.

As Dalton pointed out a bad blue 2 pin sensor on the water pump can cause that problem.

Also the relay that controls either speed could be bad.

__________________
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Outstanding I checked the wire and it was almost broken off. Thanks

Sometimes we actually get one right...

. . . and that probably means somebody . . . won't say who . . . has a new engine wiring harness in their future . . .

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

Visit my Mercedes Web Page

Thanks for posting the solution to your problem. It's frustrating searching through threads and not finding out what the actual problems are.
Lots of good help on this forum.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Hey guys,

My aux. fans are running constantly, even when A/C is off. I thought the car might have had a cool-harness installed and after some guidance from Jim, figured out that wasn't the case.

Of the threehe sensors on the thermostat housing, I've replaced the one on the far right - when facing the front of the car - thinking that is the switch for the fan. I've also replaced the relay. No change. would the other two sensors on the thermostat housing play a role here? What about the resistor? Any other ideas?

Thanks!

RJ.
'92 500e

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RJ
'92 500E
'75 Triumph TR 6

This is the sensor for aux fan coolant temp. sensing..
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU28V0O97SM&year=1992&make=MB&model=500-E-001&category=R&part=A%2FC+ACC+Temp+Sensor

..but, be aware that the a/c high pressure sw also controls the fan w/ac ON ..that is the relay that I would also check .

no, you guys nail it just about all the time!

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

PS, car is cooling off now, temp guage just crossed 80 deg. and read 65 ohm.

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RJ
'92 500E
'75 Triumph TR 6

Ok...that is close enough for the gauge to be used ..
Now, compare the ohm resistance across the blu 2 wire sensor
[ unplugged] with this chart, using the dash gauge readings as your temp input.
Remember , each index mark on the gauge is 20C. [ I see some guys read 105C as 85c , not knowing that]

Temp Ohms:

60C- 900-1800 ohms
85C- 460-650
100C- 300-400

* note
You want the highest temp reading here for testing the sensors accuracy...the lower temps ones mean very little.....

OK,

at the 60C mark, reading is 1250 ohm
at the 80C mark, reading is 670 ohm
at 85C (est), reading was 530 ohm

Hottest I could get was just shy of 90C est. where reading was 443ohm just wouldn't get any hotter.

__________________
RJ
'92 500E
'75 Triumph TR 6

....and did the high fan ever come ON with the sensor plugged back in????

Yes, whenever its above 85(est) fan goes on (high)

__________________
RJ
'92 500E
'75 Triumph TR 6