E430 AC Auxiliary Fan Not coming on... - Mercedes-Benz Forum
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post #1 of 12 (permalink) Old 08-27-2011, 06:53 AM Thread Starter
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E430 AC Auxiliary Fan Not coming on...

I have a 1999 e430 which has lost power to its twin Auxiliary AC Fans. The fans are suppose to come on automatically when the AC is on, but no longer do. The AC does still work, but barely in recent 100 Houston temperatures without the fans working.

I know it is not the fans themselves in that they will come on if hot-wired from the battery with a probe intersecting the lead in wire at the point of connection to the fans. (btw, warning. Don't try permanently doing this by tying the wire into the headlights. It will either blow the fuse, or start smoking)

From my research, the obvious culprit should be the Auxillary Fan Control Unit, a finned box that mounts under the drivers side headlight. I bought and installed a new unit, but that didn't change the problem. There does not appear to be any other fuses or relays involved in the system according to several mechanics I have spoken with. The wires appear fine.

I suppose there is an off chance that the new AFCU I bought was faulty, but am not yet ready spring another couple of hundred for another one until all else is ruled out.

Any ideas and /or a link to an AC wiring diagram or schematic would be appreciated.
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post #2 of 12 (permalink) Old 08-27-2011, 10:43 AM
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I suspect you just have too little refrigerant to trigger the fan. When I added 134a to my '97 the fan started to run briefly, switching on and off, with the low side pressure at 25 lbs and ran continuously at about 35 lbs.
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post #3 of 12 (permalink) Old 08-27-2011, 12:58 PM
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Why are you worried. The aux fan only comes on under two different conditions! The engine coolant is very high or 2 the refrigerant temp is way high If it running when your AC is on you have a BIG problem.

Go back and run the AC diagnostics outlined in the stickies. Post the data and faults and I am sure you wil get loads of advice. Good Luck
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post #4 of 12 (permalink) Old 08-30-2011, 11:00 AM
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I'm quite sure your aux. fan should come on when the A/C is on, if the A/C is properly charged up with 134a.
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post #5 of 12 (permalink) Old 08-30-2011, 11:35 AM
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my electric fans run all the time AC is on. Depends on temperatures only the speed changes.
Check stickes for clima system errors check. There is also procedure to force the computer to activate the fans.
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post #6 of 12 (permalink) Old 08-30-2011, 12:49 PM
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If your aux fan runs when you turn on your AC there is an issue with the refrigerant temp being to high or there is an issue with the coolant temp sensor being faulty.

That is why I suggested to run the AC fault test to determine the conditin of the sensors!!
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post #7 of 12 (permalink) Old 08-30-2011, 01:04 PM
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Well.. my system checks perfect and all 9 Mercedeses I do/did own had the fans running with AC on.
Not sure about W123 so.
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post #8 of 12 (permalink) Old 08-30-2011, 02:30 PM
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On both of my W124 and W210 E320 the aux fan come on low speed with AC on and high speed if the coolant temp pass 102 C.

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post #9 of 12 (permalink) Old 08-31-2011, 06:06 AM
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You have an issue also!!
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post #10 of 12 (permalink) Old 01-31-2016, 04:21 PM
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e 320 98 my is not on ,when car on, auxiliary fan not on at all,, why
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