Auxiliary fan electrical problems.

[bullmand]

I'm trying to figure out what I need to get my auxiliary fan working and I have a few questions.

1. Does this fan come on only in conjunction with the AC, or does it come on whenever the coolant reaches a high enough temp to turn it on?

2. I've tested the switch by jumping the pins as described in the Bentley and the high speed works fine. The low speed relay clicks but the fan doesn't come on. Does this mean the resistor is toast? Could it be a fuse?

3. bimmerparts.com shows and resistor and a diode. Where does the diode live and could it be the problem?

The fan has never come on at all while driving the car. My AC does not work, but I've turned it on to try and get the fan on but no luck. Also, due to a bleed screw problem the temp got up to about the 3/4 mark the other day and the high speed fan never came on. I suspect that means the temperature switch is bad, but if it only comes on when the AC is on I guess the switch may be OK.
Thanks in advance for any help/advice.

[D. Clay]

The switch in the radiator must be submersed in coolant to read accurately. The fan should run at all times when the A/C is on. The diode is on the fan bracket. I'm not sure but it may make the fan a two speed deal.  Bypass the diode to check the fan motor also. A new OEM fan is $400. I'd go used or an aftermarket, biggest size that will fit and over 2000 CFM. About $70-$100.

[Febi Guibo]

I need to post a pseudo writeup, but basically I have a four-prong relay on my single speed electric fan (hot, ground, and two wires going to a sender I had mounted in a custom radiator hose connector,

(eg, D. Clay's comment re: the switch in the radiator must be submersed etc.)

I'm not sure about the diode etc.

how exactly do you have the sender hooked up?

I will prolly be changing coolant soon, and will send a pic of the radiator hose connected... basically a length of aluminium conduit with a bung tapped for the sender.

[bullmand]

Thanks for the input. I suspect that the temperature switch may not be fully submerged due to the slight leak I'm having, but I'm still not clear on the operation of the fan. Will it come on without the AC being on? BTW, this is the stock auxiliary cooling fan on the front of the radiator. All of the wiring is stock as far as I know. I've only had the car a couple of weeks and I'm trying to get all the basic mechanical issues resolved before the upgrades start.

[D. Clay]

Fan works with A/C and also through the temp sensor in the coolant. Not sure which is hi speed and which is low.
There is also a low pressure switch in the A/C system that will not come on unless there is sufficient freon in the system. It's usually on top of the drier.
http://realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=64_0742&hg=64&fg=60
Number's 19 or 20.
With the A/C on you have to jump this switch also.

[bullmand]

Yeah, I suspect that there is no freon in the system. I don't know when the AC last worked. This is going to be a autocross/track car so I'm not worried about fixing the AC, I just want that stupid fan to work like it's supposed to. Is there a fuse for the AC somewhere other than in the fusebox?

[Vladi]

The fan works all the time when you press the A/C button and when the coolant temp. reaches 91 C / 195.8 F.
There are no more fuses except the ones in the fusebox. My resistor was toast some time ago and just took it out and hotwired the fan. So now it works only at high speed.

[bullmand]

Thanks, Vladi. I think that pretty much narrows down my problem. The fan doesn't come on when I turn the AC on, but the high speed works when I jump it. I think I'll replace the resistor and see what happens.