Auxiliary Fan (Compression Shroud) DIY [Air Conditioning]

[Turbo_Bimmer]

Originally Posted by corNIC

Okay I'm talking about that smaller wire on the fan connecter. I can not get this fan to spin even directly connected to my battery like at ALL. However when I try directly connecting the fan to the battery, with that smaller black/green wire plugged into the terminal it will try and jolt it. I'm beginning to wonder if that wire is a ground?

That small wire comes from the DME to control the speed of the fan. The DME sends a signal with a variable duty cycle to vary the speed.
According to the schematic, the output of the DME grounds the small wire through a resistor to drive the base of the PNP transistor inside the fan.
So, if you want to test the fan on the bench, you should apply 12V to the terminal corresponding to the positive big wire, ground to the negative big wire, and ground (continious or intermittent) to the corresponding terminal of the small wire with a current limitting resistor in serie (value around 50 to 100 ohms). If it doesn't turn, try to lower the value of the resistance.
The fan shoud turn. Don't let the fan turn for too long though, the transistor won't be in an correct air flow to cool down if tested on the bench.