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  #1  
Old 08-09-2009, 12:52 PM
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85 300SD auxillary fan

My fan never comes on even with A.C. on and temp. gauge at 90C.It makes an attempt to start but never does.If I jump the wires that I believe are for the temp.on off switch on side of drier it does not come on.If I jump wires at top of drier it comes on and spins fast.I moved relays around for the aux. fan and got nothing.I've read that the resistor could be bad but I cannot locate it and if I did how would I check it?Just jump from one side to the other on it?
Questions are:1.When should the fan come on?
2.Where could my problem be?
After doing extensive search on this matter I found that the wires on top of the drier with pigtails are for the temp. control switch which when I connect them the fan comes on.I think that it is a a new style replacement switch because it has red plastic at the base of it and that I cannot swap it out w/o loseing my freon.
Maybe my fan is working maybe it never came on yet because the temp. never got over 100C yet on my guage.


Last edited by yuke; 08-09-2009 at 04:55 PM.
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  #2  
Old 08-09-2009, 08:26 PM
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In most vehicles the fans should come on whenever the A/C is on and sometimes when the defrost is one.

If your vehicles is not turning on with the A/C then I would keep looking for a problem.
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Old 08-09-2009, 11:05 PM
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Originally Posted by Gene Horr View Post
In most vehicles the fans should come on whenever the A/C is on and sometimes when the defrost is one.

If your vehicles is not turning on with the A/C then I would keep looking for a problem.
These are factually incorrect statements for that vehicle.

The auxiliary fan will operate when the temperature switch on the dryer closes. If the switch can be jumped and the fan operates properly, the switch is bad and needs to be replaced. This assumes that the temperature of the system is high enough to trip the switch. It would require running at idle for about five minutes in relatively warm ambients until the system pressure climbs to the necessary level.

Some of them are in the sealed system and some are just in the housing in a blind hole.........there is a difference.
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Old 08-10-2009, 12:00 AM
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Originally Posted by Brian Carlton View Post
Some of them are in the sealed system and some are just in the housing in a blind hole.........there is a difference.
So Brian, How do you know the difference? Start to loosen the fitting and watch/listen for escaping freon?
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html
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Old 08-10-2009, 12:09 AM
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Originally Posted by Cr from Texas View Post
So Brian, How do you know the difference? Start to loosen the fitting and watch/listen for escaping freon?
Can't recall........you can tell by the switch..........others will know.
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  #6  
Old 08-10-2009, 02:29 AM
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85 300 SD auxillary fan

Brian I tried to loosen the temp. switch and could not.I too cannot tell if it goes into a blind hole or if I loosen or break it my freon will escape.I also read that maybe I have a bad resistor or bad connections at resistor but have been unable to locate it.Would appreciate any more info on the matter.At this point I am thinking to just run some wires off the switch to a toggle switch and turn it off and on as needed.
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Old 08-10-2009, 08:18 AM
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Originally Posted by yuke View Post
Brian I tried to loosen the temp. switch and could not.I too cannot tell if it goes into a blind hole or if I loosen or break it my freon will escape.I also read that maybe I have a bad resistor or bad connections at resistor but have been unable to locate it.Would appreciate any more info on the matter.At this point I am thinking to just run some wires off the switch to a toggle switch and turn it off and on as needed.
The only problem is the switch. For the system to run properly, it has to be replaced.

Or, you can run your own switch into the cabin......................
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  #8  
Old 08-10-2009, 09:49 AM
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auxillary fan

Hear is something I found in my search that I will try and might help other people to test their temp. switch.Thanks for the response Brian

Attached Files83-532actempsw.pdf (116.6 KB, 2 views)
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  #9  
Old 08-10-2009, 12:10 PM
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auxillary fan

I should of listened to you Brian I tried to unscrew my temp. switch today very slowly when I got to a certain point I did start losing oil and freon I quick tightened it back up but probably lost 1/2 oz. of oil and some freon.I hope the system can tolerate the loss and does not affect my cooling as it was'nt that great to begin with about 38 to 40 most of the time.I'm going to give up replaceing and testing the switch unless i get more info. on it and maybe I'll just wire up a toggle switch to the dash to put the fan off and on as I think it is needed.

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