aux fan - BMW Forum

miami325e · 06-12-2006, 06:24 PM

i applied 12v(jumped directly) to the auxiliary fan through the switch and it didnt come on in low nor high speeds. What could be wrong? The switch?or the actual fan? What is the function of the auxiliary fan? And how does it affect the operation of the air conditioning system?

drz · 06-12-2006, 06:33 PM

If you are applying 12 V directly to the fan and it does not run, then the fan is bad. Make sure you bypass the switch when you do the testing. The fan keeps the radiator, and hence the engine, cool whenever it gets too hot. The aux fan usually comes to the rescue when the car is idling, and always comes on with the A/C. YOu will not be able to run your A/C while idling if it is hot outside if your Aux. fan is not working. (1) The air will come out warm, and (2) Your engine will overheat.

YOu can do without it, if you remember to turn off the A/C when you are riding at really slow speeds or idling. It is a real pain and very dangerous since you may forget.

I bought a cheapo Taiwanese aux fan off eBay and installed it with my little sister's help. I have had no trouble whatsoever.

If you liev in Miami, like your handle suggests, I would say you need to change that fan urgently.

miami325e · 06-12-2006, 07:03 PM

how do i bypass the switch?

this could maybe explain why maybe my ac doesnt throw cold air.

miami325e · 06-12-2006, 07:04 PM

is the switch where i applied the 12 volts directly right on the side of the radiator?

drz · 06-12-2006, 07:23 PM

YOu shouldn't apply 12 V to any of the pins in that switch. To simulate either high or low speed situations, jumper from the middle pin to either of the other two pins on the connector (the thing you unplug from the switch, which -- yes -- is the thing on the side of the radiator, on the right side of the car).

The way the switch works, it pulls either of the two outside pins on the connector low (B- potential, chassis ground) if the corresponding fan speed is necessary. The middle pin on the connector provides the switch with B-.

I think you should be able to run this test with the engine off. But I am not entirely sure. It seems to make sense, since it is entirely an electrical thing, and some people actually have trouble with the aux fan sticking on even after they turn off the engine.

A quick-and-dirty that should work -- somebody please correct me if I am wrong -- is to just turn on the A/C. The aux fan should come on regardless of the state of the switch.