Asus CROSSHAIR IV EXTREME User Manual page 111

You need to connect the thermal sensor cables to the OPT_TEMP1/2/3
connectors to enable this function.
OPT Fan 1/2/3 Duty [50%]
Allows you to set the fan duty cycle. This item appears when the OPT Fan 1/2/3
Control item is set to [Duty Mode].
Configuration options: [40%] [50%] [60%] [70%] [80%] [90%]
OPT Fan 1/2/3 Low Speed Temp [25˚C]
Allows you to set the temperature at which the power fan rotates at low speed.
This item appears when the OPT Fan 1/2/3 Control item is set to [User Mode].
Configuration options: [25˚C] [30˚C] [35˚C] [40˚C]
OPT Fan 1/2/3 Full Speed Temp [60˚C]
Allows you to set the temperature at which the power fan rotates at full speed.
This item appears when the OPT Fan 1/2/3 Control item is set to [User Mode].
Configuration options: [60˚C] [70˚C] [80˚C] [90˚C]
ROG Crosshair IV Formula 3-35