Macpro fans

[cowasaki]

Probably asking the reverse question to most but I have a dead Mac Pro and there a four nice fans in there. I have extracted them but cannot get them to turn. There is a four pin header with ground, VCC, OP and VM

Sticking 12v and ground into the fan does nothing but there are then two additional pins. Allegedly 2.5-5v to be me of these changes the speed but I can’t get anything to happen with any of the four fans.

Any ideas?

[tooki]

Allegedly 2.5-5v to be me of these changes the speed but I can’t get anything to happen with any of the four fans.

Say what now?

[cowasaki]

Allegedly 2.5-5v to be me of these changes the speed but I can’t get anything to happen with any of the four fans.

Say what now?

I typed this on the phone which has a tendency to mess around with spelling or whole words!

Allegedly 2.5-5v on another pin changes the speed but I can’t get anything to happen with any of the four fans.

[Nominal Animal]

According to this, the pinout is GND, 12V (VCC), tachometer output (O/P), and Motor Voltage (VM).

VCC is used for the tachometer logic, not to power the motor.  The motor is actually controlled by a 2V - 12V voltage on the VM pin – this is MUCH wider range than the typical ~ 7V to 12V on 3-pin PC fans.  Apparently, for "normal" speeds, VM is about 5V, which, again, is very low for typical voltage-controlled 12V fans.  The motor current is drawn on the VM pin (the ones on Mac Pro 5.1, up to 750mA).

So, I suggest you try connecting VM to +5V, and GND to ground (these are the two outermost pins), and you should get them spinning at a "typical" speed.
(I would not be surprised to find out they're not rated to run at +12V continuously.)