Author Topic: ac button not turning aux fan (Read 4216 times)

monty23psk · « **on:** November 09, 2008, 09:48:00 PM »

hey guys,

I really have a weird issue. My aux fan is not working with ac button. But if I jump the 3 prong connecter I get both low and high speed. While troubleshooting, I got it to work with the AC button like 2 times out of the 10 or so tries. I know my AC is blowing cold and warm. Warm when the fan is not working. Not sure if I have an AC problem and because of this, the aux fan is not kicking. Everywhere I researched, said the fan should come on with the button, but I would like to know if there is an AC issue, would the fan not turn on? Looking at the ETM, the signal to the low speed has to go thru 2 AC sensors and then a diode before it hits the low speed relay. Does anyone know about this. I will start to troubleshoot the AC more closely tomorrow but hopefully someone has gone thru this.

thanks.

monty23psk · « **Reply #1 on:** November 10, 2008, 07:55:48 PM »

Ok, have an update. After researching many post and going over the wiring diagrams I decided to check something. When I click the AC button, I do not get any voltage towards the aux fan. When I jumper the low or high temp switch at the radiator, I do get voltage. So now I know the issue is with the AC. In the ETM, there is a diode in the fuse box. Bimmerparts.com has a part listed. Has anyone ever replaced this or know exactly where it its. Might look like this.

Next step is to look for that diode. My AC works as long as I have cooling towards the condenser. I could have some other issue with AC and thats why the fan is not turning on, but going one piece at a time.

thanks for any input.

monty23psk · « **Reply #2 on:** November 10, 2008, 07:57:05 PM »

Ok, have an update. After researching many post and going over the wiring diagrams I decided to check something. When I click the AC button, I do not get any voltage towards the aux fan. When I jumper the low or high temp switch at the radiator, I do get voltage. So now I know the issue is with the AC. In the ETM, there is a diode in the fuse box. Bimmerparts.com has a part listed. Has anyone ever replaced this or know exactly where it its. Might look like this.

Next step is to look for that diode. My AC works as long as I have cooling towards the condenser. I could have some other issue with AC and thats why the fan is not turning on, but going one piece at a time.

thanks for any input.

monty23psk · « **Reply #3 on:** November 23, 2008, 02:39:37 PM »

Well today I took my fuse box apart to look for and test this diode. Super easy to find and get too. Tested it and its bad. Will be getting one this week and hope my aux fan will work with my AC button on. Will keep everyone posted.

dark_islight · « **Reply #4 on:** November 23, 2008, 05:14:26 PM »

Had the same problem but the resistor on the aux fan was blown.

monty23psk · « **Reply #5 on:** November 23, 2008, 11:01:48 PM »

Yeah, well my first resistor was bad, due to aux fan motor seized. Then it did after a new resistor and new fan. Then I replaced it and had same thing happen. Resistor checked out ok and would work just fine, just not with AC button. So now I have 2 good resistors but one bad diode.

monty23psk · « **Reply #6 on:** November 28, 2008, 12:17:37 PM »

Update.... Got a used diode from the junkyard, the cheapest new one would have cost me $24 with shipping. Now everything works!!! I now have the fan working normal with the AC button depressed. So now in hot sunny weather, and stop and go traffic, I once again have ice cold AC. I do have 2 extra ones that tested fine if anyone needs one. Cost me $1 each and just need to pay for shipping.