Subject: Re: Auxiliary fan BMW 528i Author: jimcash : member since July, 2005 : 1384 posts Posted on: 2006-02-20 11:16:50

That fan is a very complex circuit, and yes there are various versions. Your car should have a 2 speed fan (low, mid and high) useing the 2 resistors to obtain the 2 lower speeds. The later cars changed to a variable speed fan that is controlled by the engine computer only. And just to make things really complex a number of the early cars were retrofitted to the later fans becasue of faults that were causing fires.

It "sounds" like yours may still be the original 3 speed version. While it does operate on 12 volts each of the 3 speeds is activated by a separate fuse and relay. So three fuses and 3 relays all at different locations (some in the Ebox and some behind the glove box).

WHen you turn on the AC the fan should normally operate on low speed depending on several circumstances:
- the mid pressure switch in the compressor has closed
- the outside temperature is reading above 10C (instrument cluster)
The fan also goes to low speed if the lower temp switch in the rad closes (91C). This is a separate parallel circuit to the low speed relay.


The fan will go to medium speed if the high pressure switch closes in the compressor. This bypasses one of the 2 resistors.

THe high speed is activated only by the high temp contact in the rad switch (99C).

Without a full schematic it is almost impossible to test all the circuits. Assuming that you can turn the fan easily by hand then it is not seized.
THe resistors are a common fault, and yes they can be replaced separately from the motor.

You can perform a simple circuit test. Remove the connector from the temp switch on the rad and short the contacts. THe brown wire is ground, and all you have to do is apply that ground to one of the other leads (one at a time). That will send the operate ground to the low and high speed relays - if they operate then the fan should run at those speeds - assuming the fuses and resisistors are OK.
NOTE - the fuses are large ones and are not located with the normal banks of fuses but are also hidden in the Ebox or behind the glove box).

If you do get the low speed fan, but it still does not run when the AC is on then you probably have a pressure fault with the AC, or the outside temp is below 10C.

I would also have the cooling system checked for holding pressure and properly bled. The car should not really be overheating just because the AC is on unless you are in very warm conditions, or if the mechanical fan is not performaing correctly.

Cheers
Jim Cash

• Auxiliary fan BMW 528i - nb0474 2006-02-20 10:52:26 (731 views)
  • Re: Auxiliary fan BMW 528i - jimcash 2006-02-20 11:16:50 (883 views)
    • Re: Auxiliary fan BMW 528i - nb0474 2006-02-20 12:23:56 (528 views)
      • Re: Auxiliary fan BMW 528i - jimcash 2006-02-20 12:47:13 (728 views)
        • Re: Auxiliary fan BMW 528i - 88x6i 2006-02-20 14:36:07 (511 views)
          • Re: Auxiliary fan BMW 528i - nb0474 2006-02-21 12:45:04 (459 views)
            • Re: Auxiliary fan BMW 528i - nb0474 2006-02-21 13:19:16 (463 views)
              • Re: Auxiliary fan BMW 528i - sanders 2006-02-21 13:48:03 (449 views)