Test if Fan Works?

[L84THSKY]

Read post #16. It explains how to jumper the low speed fan relay, and test the low speed fan. That will tell you if everything is working in the fan.

Originally Posted by b.u.ti-ful

My car overheated and some checking shows that the fan is not working.

My 1996 has a two speed electric fan and when I jumper the sensor on the side of the radiator I can get the high speed to run, but not the low speed.

The relays are good (swap) and I am inclined to think it is the low speed resistor mounted on the fan.

Problem is I don't know how to test the resistor and Bavauto does not sell one for 318ti.

Anybody know about these resistors?

[b.u.ti-ful]

Yes, I did that. It does not run on low speed.

That is why I suspect the low speed resistor, but I guess everybody just replaces the whole fan unit.

Thanks.

[JNCoulombe]

Try disconnecting the resistor and checking for continuity and whether there is voltage coming to the fan when you think the low speed fan should be running. If the resistor is bad maybe you could find one through a junk yard.

[pnosker]

A tip on burping. Put the TI's front end on an inclined surface. This helps the air move naturally to the cap of the radiator.

[b.u.ti-ful]

Originally Posted by JNCoulombe

Try disconnecting the resistor and checking for continuity and whether there is voltage coming to the fan when you think the low speed fan should be running. If the resistor is bad maybe you could find one through a junk yard.

Thats what I am not sure how to do. I have an ohm meter, but the thing has two blue and one black wires coming out of it. One blue goes to the fan. The black and other blue goes to the harness.

[b.u.ti-ful]

I know there is voltage going to the fan even at low speed because it sounds like its trying to turn on when I put the AC on. I can also hear the low speed relay clicking. I am assuming the fan motor is fine because it works on the high speed jump test.

[b.u.ti-ful]

I guess junk yard is the only option besides a new fan unit which is around $300!!

Thanks to everybody trying to help me out.

If I could source these resistors I'd through them out at parades.

[JNCoulombe]

From the wiring diagram I'd guess that the low speed fan input would be the black wire. The diagram shows a black wire with a blue stripe. I'd guess that you should have continuity between the blue wire to the fan and to both the blue and black/blue wires going to the harness. I'd expect a higher resistance between the blue to fan wire and the black. I was puzzled by your saying the fan tried to turn on when you turn on the A/C. I thought that the high speed fan should come on when the A/C was turned on.

[b.u.ti-ful]

I tested the black and blue at the plug end of the wires coming from the resistor and its the same reading as when the tester is not hooked up at all. I take that to mean the resister is no good, but I admit I have little experience doing that sort of test.

The low speed setting comes on when you turn the A/C on (even if the engine is not very hot) If the engine gets too hot it switches to high speed.

[JNCoulombe]

It sounds like you mean that there is infinite resistance between the black and the blue leads. That does sound like the resistor is bad. I don't know where you can find one new, have your tried calling any of the suppliers or even the dealer?

[b.u.ti-ful]

Yeah, it might be worth giving the dealer a call.

The parts guy at my area dealer is a good guy and will at least listen as I describe the part that has no part number. I'm not very optimistic, but I'll call him on Monday.

[b.u.ti-ful]

I talked to Bavauto and my dealer and they cannot get the Bosch resistor. I did a lot of surfing trying to find it, but without a part number it's hopeless. The BMW parts guy told me I could get a 15% discount on the new fan unit if I was a member of BMWCCA, so I joined it online and the discount will easily pay for a year membership and you get the magazine, so not a bad deal.

[b.u.ti-ful]

Put the new fan in today and everything works fine.

I talked to an electronics guy and he said if I had a working resistor and an amp clamp and ohm meter he could figure out a replacement resistor.

The new fan is a different set-up with no obvious giant resistor hanging out, so I'll leave the replacement resistor investigation to someone else.

I'm just glad to have my car working in the hot weather.

[L84THSKY]

Ever since I bled the coolant system, I haven't had a problem.

Originally Posted by gimp

^^^ air trapped in the system was my problem, with your exact same symptoms (overheating only in traffic, etc)

[dougjohnson]

Sorry to revive this old thread, but...Did anyone ever find out if the engine has to be warm for the low speed fan to come on when making a jumpered connection at the temperature switch? I am wondering if anyone out there has jumpered this connection with a cold engine and had both speeds come on? As of now mine will only work on high speed.

Doug