How to diagnose 3 pin Auxiliary fan not working

[matteds]

I have an 1999 bmw e39 523i. I can't get ac working. The aux fan never starts. I checked and it's 3 pin. I think this means I can't hot wire it to test if it works?. How do I diagnose the 3 pin aux fan.

If I simply buy a used or cheap fan can I plug it in and this should run when I hit the ac button on the hvac ?.

If I have a running fan how does it talk to the compressor and start ac working ?. I only get alot of hot air...

Thanks for your time

[BimmerBreaker]

Good chance the wiring is faulty. The car does a self test at startup, if it fails this test it throws a shadow code in the DME. CEL will not illuminate but it'll store a code and it will stop even trying to run the fan. If this code is present or if the fan is not working the A/C will not work. The 3 wire fan won't necessarily run just because a/c is on, it looks at other factors too (though usually it should run when a/c is on, this isn't always the case and can't rely on this diagnostically). Use INPA to try to trigger the fan manually and check for the code. If it works when triggered then you likely have a intermittent wiring issue. If you don't have INPA you can also have someone else start the car with you in front looking at the fan. It should spin for a moment, just a few rotations, during the self-test at startup.

In my experience with these fans, I've had to fix quite a few including my own, the issue is usually the PWM trigger wire - the small wire on the harness, it runs straight to the DME x60004 pin 4. If the fan won't run you can test this wire for continuity. If it fails continuity test or cuts in and out while moving the harness, replace the wire end to end.

If the fan runs when triggered in INPA and passes the self check but won't turn on otherwise and A/C is not cold, it is likely to be an A/C issue - pressure sensor faulty, or refrigerant level too low. However I would assume the fan/wiring is bad until proven otherwise.

[matteds]

Thanks for your quick reply BimmerBreaker.

I like to set out some more questions if I may.

I want to clarify the fuses for aux fan in my model are 7, 20, 22 and 75 ?.

Does the PMW fan have relays ?. I have a small black box called a Auxiliary Fan Sensor Relay dangling on the passenger side of radiator. Could little black box be responsible? Can it be tested ?. Is there more relays for this aux fan under the passenger air filter ?.

Sorry for sounding ignorant.

[matteds]

Ok I have figured out the Auxiliary Fan Sensor Relay dangling is not really relevant.

Can I use a logical probe tester on the 3 hole female connector presented and see if there is some kind of signal ?. I can get photos if you would like ?

[matteds]

I have taken some photos. You will see all my wires have been tampered with before me. You can see they are all stripped at one point. I also took a photo of my aux connectors.

From the pics could I use some kind of detector, multi meter to work out my aux fan issue ?
20230304_093943.jpg20230304_093831.jpg20230304_093911.jpg
Please see pics

[BimmerBreaker]

It's a PWM signal wire. Hard to verify anything off that with a multimeter except broken continuity.

I don't know the fuses off hand. Diagnosed many of these and never once has it been a fuse issue. The power wire sits behind a 50a fuse, quite large. PWM signal wire has no fuse. The ground wire grounds straight to chassis.

[BimmerBreaker]

Yeah, when the fan fails it's usually in the PWM controller on that board. Personally I've seen a lot more with bad PWM wires (affects E46 and E53 too) than I have actually seen failed fans. Imo it's always prudent to verify the wire is intact before buying a new fan. I can't count on two hands how many people brought me a car and said "I just replaced the fan and it's still not working" and the problem was the wire. The insulation dries out, gets brittle and stiff and movement/vibration starts damaging the wires inside the insulation. It becomes an intermittent problem until they manhandle the harness to replace the fan and completely break the wires inside the insulation