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  #16  
Old 07-07-2003, 02:23 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,777
Quote:
Originally posted by moedip
so if the fan comes on when engine temps are normal - chances are the sensor has failed (to be verified by checking ohmage of disconnected sensor) - right? So if I understand what you are saying. This is the only sensor (on rad hose) that will kick aux fan into high.

Correct .... or, a bad connection at the sensor connector
[ common fault] will do the same....

The high pressure sensor on a/c drier is what kicks the fan into low speed (unless load resister has been jumpered). Are my assumptions correct?
Correct....
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  #17  
Old 07-07-2003, 02:27 PM
moedip
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Thanks again Arthur - appreciate your time and expertise to clarify this for me.
Morris :p :p
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  #18  
Old 07-07-2003, 03:20 PM
moedip
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hey John - what is the outside temps when you kicked the a/c on high? Did the fan start immediately when you put the a/c on both arrows? Come to think of it - what does the unfilled arrow on top with filled arrow on bottom actually mean? what does both filled arrow switch mean? (sorry - no owner's manual)
When the outside temp here was 77F and I put the temp dial to minimum and the two filled arrow switch on - a/c cooled like a banchee and engine temp stayed below 95C for over a hour and the aux fan never kicked in.
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  #19  
Old 07-07-2003, 03:25 PM
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Join Date: May 2003
Location: Rockville, MD
Posts: 96
Morris,

The outside temp here in MD is showing as 92-93F. If I rev the engine for a bit while stationery and have the AC on, either normal (open top arrow) or multi level (both arrows filled), the aux fan kicks on after a few minutes, with the engine temp reading around 80C. Whether it is HIGH or LOW is anyone's guess. It sure doesn't look LOW to me...it's movin'! When I kill the AC, the fan turns off after about 10 seconds. Am I to assume this means the AC pressure sensor is working?

[Re the switches Normal is what it says to use most of the time. Air comes out all the vents except the defrost when cooling and all the vents including defrost when heating. On Multi Level it comes out all the vents including def. whether heating or cooling. (That is unless your center diaphragm is cooked like mine and it comes out the def. no matter what button you use...)]

When I pull the left two prong plug (which just cracked) on the temp sensor I can't get the fan to kick in. Since the plug is a bit stale, can you or Arthur suggest whether the plug or the sensor might be the problem. If the plug, is this a part I can order from Fastlane?

Thanks,

John
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  #20  
Old 07-07-2003, 03:55 PM
moedip
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John - at operating temp - I pull the plug - the fan comes on - I give the ball to Arthur!! According to his circuit description - it cannot be the connector or sensor as the ECU defaults to "on" normally.
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  #21  
Old 07-07-2003, 04:15 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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The place to look for No high fan from etc sensor is the load fuse for high fan....
Some are outside the fuse box, some are on top of the high fan relay..
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  #22  
Old 07-07-2003, 04:56 PM
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Join Date: May 2003
Location: Rockville, MD
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Arthur,

I pulled all the relays and reseated them (hoping that, I too, might be blessed by the magic moedip fix). I just replaced ALL the red, white and blue fuses. Where (exactly, since I'm new to this) should I be looking for the load fuse and the ones above the high fan relay?

Many thanks,

John
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  #23  
Old 07-07-2003, 05:28 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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Quote:
Originally posted by phatryd
Arthur,

I pulled all the relays and reseated them (hoping that, I too, might be blessed by the magic moedip fix). I just replaced ALL the red, white and blue fuses. Where (exactly, since I'm new to this) should I be looking for the load fuse and the ones above the high fan relay?

Many thanks,

John
I think your relays are under the cover behind the fuse bos.
A few screws ... check the relays there ..
I am not sure of your model, so an archieves check may help you
w/location
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  #24  
Old 07-07-2003, 06:22 PM
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Join Date: May 2003
Location: Rockville, MD
Posts: 96
I have an 87 420SEL. In the fuse box, the fuses are closer to the headlights, the relays closer to the windshield. There are six (maybe five) silver colored relays all with the same markings. I searched the archives but couldn't find what relay controls what. Any ideas on this? I may start a new thread to see if anyone knows.

John

87 420SEL
00 C230K
00 A4 2.8Q
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  #25  
Old 07-07-2003, 06:28 PM
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Join Date: Aug 1999
Location: Florida / N.H.
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I dson't have a pictoral on that models
I am sure someone knows exact location...
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  #26  
Old 07-09-2003, 09:29 AM
moedip
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One last post before I leave on my trip. John - just to make sure you know - If the engine temp. is not at 80C or above on my 560sel - I can remove the connector to the temp sensor (two wire) on the end of the upper rad hose and the aux fan will NOT default on. It will only default to on when the connector is removed if the engine temp is over 80C - must be another sensor somewhere that has to kick in before the ECU will detect an open fault when the connector is removed. Before you start condemning your aux fan circuit as faulty - try the test with the engine temp up all the way. If your fan still does not kick in when connector is removed - maybe Arthur can suggest what other sensor may be going flaky that prevents the ECU from reading the default signal when the connector is removed. I will check for your response early next week when I return.
Morris
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  #27  
Old 07-09-2003, 11:55 AM
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Join Date: May 2003
Location: Rockville, MD
Posts: 96
Aux Fax

Every time I have pulled the plug on the two prong side of the electronic temp sensor, the thermo on the dash has been showing above 80 (about 90) but the fan still doesn't come on. Thanks to Sixto's help with the relays here...

420SEL ('87) Need Relay Legend/Diagram

I switched a few relays around to see if one was bad...and everything but the fan still works. It kicks on fine when it's hot and I blast the AC but nothing when I pull the temp sensor plug. Unless someone's got another suggestion, the next step seems to be to replace the temp sensor. I'm not running MB coolant and I'm not sure what ratio mix (coolant to H2O) my mechanic put in the system. Is it possible that the coolant mixture is just not such that it will trip the ETC?

John

87 420SEL
00 C230K
00 A4 2.8Q
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  #28  
Old 07-09-2003, 12:31 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,777
Pull the relay for high fan and jumper pins 30 and 87 [ marked on relay]
Key on:
This eliminates all sensors , as it is load side ..
If still no fan, check for 12 v at pin 30 and ground..if no 12 v. , you have a feed/ fuse prob.

If you get fan w/jumper , you have a bad relay or sensor side of circuit [ coilside] problem.. In other words [ IOW] , the relay coil is not pulling in the main load contactor....
That is the sensor side of the circuit... [ relay primary/ low current side]

Last edited by Arthur Dalton; 07-09-2003 at 12:38 PM.
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