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  #1  
Old 08-04-2001, 04:26 AM
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Join Date: Aug 2001
Posts: 22
Auxilary Fan Problem

Hello everyone, I am kinda new to all this but i can get use to this.
Anyways I have a 87 260e ... I am having problems with ma AUXILIARY FAN ..... it keeps running no matter what
car is started, car is cold, the A/C is on or off......
it seems to just keep running?
what could be the problem?
and how can i fix it??????????????????????????
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  #2  
Old 08-04-2001, 08:07 PM
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aux fans

The aux fans are controlled by several switches and relays. Have you owned the car long? Can I assume that this problem just started, recently? If this has been going on since you purchased this car, then someone may have bypassed a switch to keep the fans on, probably to correct a overheating problem.

If this problem just started, then I would check the switches first then the relays second. Start by turning on the car, but don't start the engine. There is a switch in the top of the A/C drier, (drier is located behind driver's side headlamp assembly, black cylinder) it's red and has 2 wires made onto it. Unplug one of the wires and see if it stops. If it does then that switch is bad and you will have to go to the shop and have it replaced, due to the fact that the A/C system has to be drained. The second switch is located 2/3rds of the way to the back of the head on the driver's side, between the air filter housing and the valve cover. This switch is blue and has 2 pins on top for the wires to connect. With this switch, it is easier to replace the switch to test due to the way it functions.
Next is the relays, if they are stuck in the ON position. I don't have a wiring manual at home to tell you which relays control the fan, so I can not help you there until monday .
The most common reason (I see) for your complaint is someone bypassing a switch to cover-up a overheating problem. Second most common would be the switch on the head, which when it goes bad causes the fan to run at high speed continuously and can cause the A/C compressor not to engage.
Let everyone know what you find

Hope this helps
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  #3  
Old 08-04-2001, 08:16 PM
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Posts: 22
Hey thanks alot for your help, you made it much more clearer for me. I have checked by the rec. drier i cant find nothing there . i will check again for anything but i cant find no wires or nothing maybe some1 has by passed it because when i bought the car that was like maybe 6 yrs ago the fan was continously running so all i did was disconnect the main plug coming from the aux fan so the fan wont work period. I check the coolant temp on top of the engine towards the back..... I think tthe temp sensor if fine
Most likely it looks like they by passed the drier.... what should i do to fix it up again n make the fan work with the car's temp and with the ac on?????
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  #4  
Old 08-04-2001, 08:44 PM
benz560sel
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560SEL same problem

I have a 1989 560 SEL with the same auxillary fan problem. Can someone help me figure out the wiring and switches for testing to see if it's a switch that's bad? Thanks in advance.
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  #5  
Old 08-05-2001, 02:43 AM
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Join Date: Aug 2001
Posts: 22
ok i figured out the problem and all to ma aux fan
my aux fan switch has a wire that is comin from the relay box..... that makes the fan go on continously.... i took that lead wire out coming from the relay box and the fan stop working now.....
how will i know now if ma fan is working properly?
can i do some tests? i mean it finally stopped and before it would runn continously but now i took the wire out from the relay box to the aux fan switch in the drier and the fan stopped....
will m yfan work now?
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  #6  
Old 08-05-2001, 01:59 PM
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to: dnkyliquid

I'm having a hard time making sense of your post, so I will ask a couple of questions to help clarify things for me.
I gather that this problem has been occurring since you purchased this car, is this so?
I gather that you found a wire attached to the aux fan relay, is this wire something someone added or is it factory? If it's factory it will be in a harness with other wires.
Does the red switch on the drier have 2 wires made onto it and are they both plugged into wires coming from the main harness?
Does your A/C work? Blow cold air? If it does, the switch in the drier works on high side pressure of the A/C system. Without A/C gauges and knowing how to use them, it would be hard to explain how to test this switch.
Let me know the answers to these questions and we'll work on it some more.
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  #7  
Old 08-05-2001, 03:14 PM
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to: benz560sel

Your 560SEL has the same basic switches and relays as the 260E.

Does your aux fan start running the minute you turn the key on? before you even start the engine? If so, you have a problem.

Please re-read and refer to the post I wrote originally. it has useful info, and will save me a lot of typing.

I personally see the temp. switch causing the problem mostly. on your car. The blue 2 pole temp switch that is used for high aux fan is located at the front of your engine, next to where the upper radiator hose attaches to the engine.

Let us know if you find anything, or have more questions.
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  #8  
Old 08-05-2001, 03:19 PM
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Thanks alot
OK, this problem has been since i bought the car.
There is a wire some one put in that is connected to one of the wires from the ac drier switch and it goes all the way to
the relay box and is connect with on of the relays....
My A/C works totally fine and all. Now i took the wire comiin from the relay box and disconnected it and the fan does not run continously no more. Do you think it is working properly now
or do i have to change the switch comin from the ac drier??????
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  #9  
Old 08-05-2001, 03:39 PM
benz560sel
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MB Medic

My aux fan turns on when i turn the key but before i start the engine. Sometimes it does it, sometimes it doesn't. It's weird that it doesn't always do that, do you have any explanations for that?

Should i test the blue 2 pole temp. switch first? Or do i have to test the red switch first?

Assumming it's the blue 2 pole temp. switch, how much is it? is it a difficult thing to do myself? How do i go about changing it?

Thanks in advance.
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  #10  
Old 08-05-2001, 04:24 PM
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dnkyliquid

Thanks for the clarification.

As for is the fan working properly now question, If the outside temp is say 80+ and you start the car and turn on the A/C and let the engine idle. The aux fan will probably come on in 10-15 min.. You could rev the engine to around 2500rpm to speed the test, because it raises the high side pressures. To accurately tell if the drier switch is working correctly you would need to put A/C gauges on the system and read the high side pressures, when the pressure reaches 300-325psi on the high side then the fans are switched on until the pressure drops below 275psi then they are switched off.

If you unplug the blue 2 pole temp switch the aux fan should run on high speed.

Keep a watch on your engine temp, esp. in traffic, to make sure you have no overheating issues. The temp. should not go over 105c if it's 95deg outside with high humidity, like it is here in GA.
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  #11  
Old 08-05-2001, 04:36 PM
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benz560sel

Sometimes it comes on, sometimes it doesn't? I have a question on that. Does it come on when you first go out to start the car? Before it has been run at all that day? or only after it has been driven and parked for a short time?

read the last post to dnkyliquid, it will help explain what makes the switches activate
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  #12  
Old 08-05-2001, 07:34 PM
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Join Date: Apr 2001
Location: Near Omaha Nebraska
Posts: 19
Question Question on fan turn on temps

I have an '87 300SDL, and the engine temps. seem to get higher than I think they should.
I checked the CD data sheets for the car, and it looks like the Aux fan turns on at 105'C in "low" speed (resistor in line), and steps up to high speed (resistor bypassed) at 115'C.

This seems to be a bit high to me, and makes me worry. The engine does get up to about 105-110 at times. Is this normal?

On another point, at what temps should the visc. coupled fan driven by the engine start to engage/tighten up? I have had the engine temp at 105C by the guage, and have watched the fan while running the engine RPM up a bit from idle.. it does not look like the fan speeds up at all at this temp.. is that the way its supposed to be? Kind of like a constant speed (which rises with the air temp), no matter what the RPM of the engine?

Any insight to the visco-fan or comments on the fan-engine temp switch would be helpful!

Thanks in advance!
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1985 300D - 190K Miles - 26 MPG on first trip home - getting rust fixed and repainted.
1987 MB 300 SDL - 238K miles - Sold
2003 DC Ram 2500 QuadCab 6 speed, 4x4 Cummins - 82K miles - 20+ MPG
1999 VW A4 Jetta TDI 5 speed - 83K miles - 50+ MPG is easy!
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  #13  
Old 08-05-2001, 11:23 PM
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Join Date: Aug 2001
Posts: 22
hey thanks alot for the the tip man
its helping me alot and im understanding the whole system and all. I will check those tests and all and see what happens and if the fan doesnt go on at all........
what is the problem then?
should i change the aux fan switch
or the coolant temp sensor????????
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  #14  
Old 08-06-2001, 12:08 AM
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to: vhunter

Your 300SDL has a different type of engine temp. switch. It's a 3 pole switch, 1 pole is a common and the other 2 poles activate separate relays for low and high aux fan speeds. Your car also has aux fan switch in the A/C drier. See earlier posts.

As for the viscus fan clutch, when the engine is warm it should be almost "locked in" with the engine speed until 2000 - 2500 rpms.

If your engine runs that warm (105-110) while driving down the road at 40 -50 mph, then you have restriction in your cooling system. The most common restriction is the thermostat, then the radiator next.

If your engine runs 105-110 only at idle with the A/C on in traffic on a 95deg. day, check that your aux fan is running. Does it cool back down within a mile or two when you get moving again?

Give me more info as to what the circumstances are when your engine runs 105-110deg, and we'll go from there
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  #15  
Old 08-06-2001, 02:30 AM
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Join Date: Apr 2001
Location: Near Omaha Nebraska
Posts: 19
Runs warm when....

Well, with the AC off, it stays around 80-90C even with the hot 95-100 deg days we have been having. With the AC on and driving stop and go style, in town, it will creep up, the highest being about 110-115 or so.

When driving on highway, above 40 MPH or so, the temps will slowly drop back down to 90 or 95 with the AC on.. So, it seems to me to not be getting enough air thru until the car is moving fast enough to force it thru the radiator. I have seen the Aux. fan kick on when the AC compressor starts up, but I'll have to check on the switch for the engine temps... I know the CD talks about it not going on low until 105C is reached, and high at 115C. I have not tested this out yet, but if I can get time I will check the switch out... also the resistor, to make sure that it is not open.

I would not have thought that the temps would get that high just sitting there at idle if the Visco-clutch was functioning. I did a crude test to see if it would speed up with the engine RPM the other day when the water gauge was showing 105+, and it seems to not show any change in speed when the engine is speeded up from idle to about 2K RPM... I really don't want to buy a new visco-clutch until I am sure that is the problem. But it seems to be pointing that way.

Any of your thoughts on this would be a help in starting me in the right direction. If I had someone in the area who had the same type of engine, I could compare the fan clutches to see if they operate the same at the same temps.. but for now I don't know of anyone in the area.

By the way the engine has 230K miles on it, so it is not that far of a jump to think that the clutch could be worn out!
__________________
1985 300D - 190K Miles - 26 MPG on first trip home - getting rust fixed and repainted.
1987 MB 300 SDL - 238K miles - Sold
2003 DC Ram 2500 QuadCab 6 speed, 4x4 Cummins - 82K miles - 20+ MPG
1999 VW A4 Jetta TDI 5 speed - 83K miles - 50+ MPG is easy!
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