Confused Aux Fan Testing

[m3f_VT_M3]

Ok everyone, Here is my issue. I have been testing my aux fan because it didn't turn on when my ac was turned on. I have never had overheating problems *knock on wood*. So here is where I am confused. All of the fuses are good. When I short the two relays both speeds work. When I short the temperature switch only the highspeed fan setting will turn on. I am a little confused about what my actual issue is. Do I have more than one issue?



Thanks in advance.

[m3f_Jrrrrrrr]

If both speeds of the fan work via jumping the relay sockets, but the low speed doesn't work via jumping the temperature switch, I would check the continuity of the wire between the low-speed pin on the temperature-switch harness plug and the relay socket. Another common issue is that the low-speed relay itself burns out over time, seeing how the low-speed of the aux fan is in use more often than the high-speed. It's the low-speed of the aux fan that kicks in with A/C, so I'm guessing your low-speed relay is burnt out. A quick way to test this out if to swap the adjacent A/C relay into the low-speed aux fan slot, and seeing if the low speed of the fan then works via jumpering the temperature-switch plug.



I'm assuming you have a wiring diagram and/or electrical knowledge on hand, seeing as how you figured out how to jumper the relay sockets.

[m3f_VT_M3]

BINGO! I have a little experience, but the diagram on the side of the relay helped the most. I switched the relays and it worked great. Now just to acquire a new relay. Any good ideas about where the best place to find a new one is?

[m3f_Jrrrrrrr]

Autohaus or FCP has a new genuine BMW relay for around $15:



http://www.google.com/shopping/produ...=0CGAQgggwBDge



This yellow relay came on lots of other BMWs you might find at a wrecking yard. You can even use a generic Bosch relay provided it's rated for the current and contains a diode for circuit protection.