problem with aux fan turning on

[mikewbd]

Hi guys,

I have a problem with my aux fan on an e30. I am under the impression that there is a low and high speed setting and the fan kicks on when the car gets too hot, or also when the ac button is pressed. In my case, the aux fan*does not turn on under any circumstance. A/C switch does light up and can hear audible click from compressor when clicked (tested twice with two different switches)

First we disconnected the 3prong connector behind the driver side headlight and tested that connection. With the car on and off, and with the ac switch on and off, there was no signal in all 4 scenarios from the female side, being the side coming from the wires from the fuse box.

We then jumped the male side directly from the car battery and the fan turned on; both low speed and high speed worked.*

So we knew the fan was not getting signal to turn on and tested the fuse box.

In the fuse box, relays K1 and K6 were both good from both relay and relay box.

Fuses 3,18,19,20 were tested with car on and ac switch on. All fuses had power except 18.

I searched and found 18 is the radiator thermo switch so would only get power when triggered (like how 19 gets power when ac is on).

Not sure how to proceed because foregoing fuse 18, the ac should have prompted the aux fan to turn on but it is not.

Thanks in advance!

[jlevie]

Using the wiring diagrams from http://wedophones.com/BMWManualsLead.htm trace back from the thermo switch to find out why the thermo switch control isn't working. In the process you may find a common cause for the aux fan not coming on at low speed when A/C is turned on, or that may be a different problem.

[mikewbd]

I jumped the radiator thermal switch and only the high works. When I tried to jump the low, there was no k1 relay click. Is this a sign of a bad resistor?

[jlevie]

If the low speed relay doesn't close when you jumper the low side control the relay is bad or there's a wiring problem between the relay and thermo switch connector.

[mikewbd]

K1 and k6 relays were switched, so relays are probably fine. Besides wiring issues, could a bad resistor prevent low speed to not work when jumped?

[jlevie]

If the resistor is bad, the fan won't run on low speed when the relay closes. But a bad resistor has nothing to do with whether the relay closes.