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aux. fan not working

137K views 45 replies 17 participants last post by  GlynDanks 
#1 ·
my aux fan is not working nor turning on when the a/c is on. I replaced the fan switch that goes in the lower hose attached to the rad when I did the cooling system overhaul.
what else could it be the cause?


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#32 ·
For the crosslinked record, JimLev offers good advice here for discerning aux fan types:
Did your fan motor look like this with these color wires coming out of it?
If so, you have a PWM fan.
The older fans are 3 speed that only have 2 wires ans use relays and resistors to switch speeds.
The resistors are mounted to the fan frame.
See also:
- DIY for how to replace the auxiliary fan (1) (2) (3) & how to test the cooling system auxiliary electrical fan (1) (2) & the infamous fuse 75 (1) & the aux fan relay (1) & an exploding aux fan noise situation (1)
 

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#33 ·
For the crosslinked record, a screenshot from the Bentley on the aux fan operation is here today:


See also:
- How to test the cooling system auxiliary electrical aux fan (1) (2) (3) (4)
 

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#34 · (Edited)
For the record, this is good information added recently:

If the temp gauge gets up to 3/4'ers the fan should be on high speed! Which is stage 3. There are no resistors in the circuit for high speed.
You could have blown fuses, bad relays, or the aux fan motor itself could be bad.
You could also have bad resistors or a bad temp switch in the side of the radiator, best to have someone trouble shoot and find out what parts are bad unless you just want to throw parts at it.
Here's the circuit for the 3 speeds. Ignore the notes, they were from helping another person.



See also:
> E39 (1997 - 2003) > E39 Auxiliary Fan DIY write up-With Pics.
- DIY for how to replace the auxiliary fan (1) (2) (3) & how to test the cooling system auxiliary electrical fan (1) (2) & the infamous fuse 75 (1) & the aux fan relay (1) & an exploding aux fan noise situation (1)
 

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#35 ·
There is a good aux fan discussion today over here:
> E39 (1997 - 2003) > Over heating

See also:
- How to test the cooling system auxiliary electrical fan (1) & a DIY how to replace the aux fan (1) & where is the auxiliary fan fuse F75 (1) & where is the aux fan relay (1) & an exploding aux fan noise situation (1) & what is the o-ring size for the coolant temperature aux fan thermoswitch (1)
 
#38 ·
My car over heated I towed it to my mechanic after a couple days he called and said my aux fan needed to be replaced because it wasn't pushing hot air out while my AC was on and he said the coolant was boiling in the radiator and that's what caused my hose to blow off as well. The hose to the thermostat housing blew off
 
#39 ·
My car over heated on the highway so I pulled over immediately. Opened the hood and saw that the bottom hose of the thermostat housing came off. I towed it back to my house called my mechanic he told me that there was air in the system. I took the steps to get the air out. I turned the car on and let it idle the needle went to the middle then went a tad bit over the middle and went back. It did this a couple times. Then it started to go over to the HOT area really fast I turned off the car then I see steam coming out. I opened the hood and saw that the hose blew off again. I tow it the next day to my mechanic he did a pressure test and everything was fine. He let the car cool off for the day and the next day called me and told me that the AUX fan wasn't working and this is what caused it to over heat. Mind you, while I was letting it idle I had the heater on and it was bleeping hot air then I turned the AC on. I'm thinking that's why it over heated and blew the hose off again???? Pls let me know what everyone thinks! Thank you
 
#40 ·
As far as the Aux fan is concerned it's very easy for a mechanic to determine if it's working properly or not, I had overheating issues a few months ago on my E39 and it turned out to be a tiny leack /side crack on the radiator. Water was being running off. A couple of months later when it got hot the Aux fan ceased after working unexpected for a couple of weeks in a row...New fan and that was the end of that although to be fair it was a 15 year old original fan and summers in Cyprus are 35 -41 Celsius for days in a row.
 
#44 ·
Hi,my aux fan was not working when i bought the car (crafty seller had the climate control set so it wasn't noticeable),after struggling with the cooling system "dumping" hot air into the cabin even in our mild English temps. i decided to get it fixed and purchased a aux fan from ebay which i thought was new but i'm not too sure now because although it works okay- after a few months the fan blades seemed to be catching on the mesh part of the shroud(if i open the hood ! the noise stops but starts again after its closed, if i ease the bonnet up it goes away)I assumed that something had moved but my mechanic says its the bearing thats worn and the blades are out of line,anybody else had this problem ?Thanks Glyn.
 
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