Did you mean like when you are running the 12v line only?, for fans,TEC,ect?...
Cause the 12v line is tied to the 5v line, unless the 5v line is drawing current the 12v lines is 'capped' at the lowest ampage. I
think it's a resistor you have to solder on the 5v line to get it to draw current...
I read an article or thread about it at coolhardware.co.uk a while back and can't remeber the details
...