Auxillary fan always on

[bmwpower]

What would cause the auxillary fan to stay on ALL the time with the ignition on, even when car is COLD.

Fan and resistor are virtually brand new.

Thanks!

[Ross]

Bad temp switch, fused relay

[632 Regal]

Check the relay. Switch it with a known good one and that should do it.

[bmwpower]

Which relay are we talking about? The one under the seat? Or are you talking about the thermo switch on the rad?

[632 Regal]

I would check the rad switch first for continuity when cold and then try the relay. The relay is uncer the hood, not sure which one... cant find my scematic right now. Ill look around.

Which relay are we talking about? The one under the seat? Or are you talking about the thermo switch on the rad?

[Adnan]

What would cause the auxillary fan to stay on ALL the time with the ignition on, even when car is COLD.

Fan and resistor are virtually brand new.

Thanks!

Hi,

I had the exact same thing happen on my '91 535i so I pulled out the ETM and started to go through the schematics. There was only one possible culprit, based on what I could tell. Are you ready for this - it was the airconditioning pressure switch.

The simple yes/no test is to unplug the wiring to that switch and see if the fan stops. If I recall correctly, the switch fails to a short. An easy test with zero cost and about three minutes invested. I did that and can also confirm that the switch I removed was a dead short.

I had to evacuate the system first since removal of the switch will dump all of that R12. The switch is located under the washer fluid reservoir and is pretty easy to unscrew. I installed a new switch and the problem was completely cured.

Good luck,
Adnan

[bmwpower]

I would check the rad switch first for continuity when cold and then try the relay. The relay is uncer the hood, not sure which one... cant find my scematic right now. Ill look around.

Bingo.

Checked the rad switch this morning and it failed the test.

Rad switch on order.

[bmwpower]

Hi,

I had the exact same thing happen on my '91 535i so I pulled out the ETM and started to go through the schematics. There was only one possible culprit, based on what I could tell. Are you ready for this - it was the airconditioning pressure switch.

The simple yes/no test is to unplug the wiring to that switch and see if the fan stops. If I recall correctly, the switch fails to a short. An easy test with zero cost and about three minutes invested. I did that and can also confirm that the switch I removed was a dead short.

I had to evacuate the system first since removal of the switch will dump all of that R12. The switch is located under the washer fluid reservoir and is pretty easy to unscrew. I installed a new switch and the problem was completely cured.

Good luck,
Adnan

I didn't think about that. That reminds me to test that switch. I would guess mine is long since dead due to my air not working.

BTW, isn't there a schrader valve where that switch screws into? If so, you wouldn't need to dump the entire system, just unscrew it. Let me know if you remember or not. I'd like to be able to change it without dumping the system.

Thanks!

[Ross]

If this turns out to be the cause you can simply disable it by disconnecting it.
The consequence is the aux fan won't run continuously with the a/c on but will cycle according to temperature. Since your a/c is inop. why bother fixing the pressure switch?

[bmwpower]

If this turns out to be the cause you can simply disable it by disconnecting it.
The consequence is the aux fan won't run continuously with the a/c on but will cycle according to temperature. Since your a/c is inop. why bother fixing the pressure switch?

I wanted to try to get the A/C working again so I figured this would be the cheapest place to start troubleshooting.