I have on occasion controlled the fan speeds by going to:
There you will find several files referring to the fans.Code:/sys/devices/platform/applesmc.768
and many others.
Make a note first of the values in fan1_max, fan2_max and fan3_max so you know the max speed for each fan.
Then you can control them by doing:
And entering a desired value.Code:sudo nano fan1_min
fan1 is for the GPU I believe.
I have not researched the other fans.