Asus P8B WS - Manual (Page 45)

2. Chassis Fan control setting (3-pin CHAFAN_SEL)
These jumpers allow you to switch for fan pin selection. The CHAFAN_SEL
jumper is for the front fans and rear fans control. Set to pins 1–2 when using
3-pin fans or pins 2–3 when using 4-pin fans.
• If you use a 4-pin fan but set the jumper to pin 1-2, the fan you installed may
not work.
• If you use a 3-pin fan but set the jumper for a 4-pin fan, the fan control will not
work and the fan you installed will always run at full speed.
ASUS P8B WS 2-19