mobo fan headers

[ajhoranny89]

Hi guys, im pretty new here. My mobo is an asus crosshair v formula-z with 3 chassi pwm 120mm noctua fans conneted to the chassi_fan header and working all the time i turn on my pc. Thia mobo also has 3 opt_fan headers which i have a140mm noctua fan conneted on it. This 140mm fan only works when i set to duty mode at 50% or higher. When i set to user mode it dont turn on at all it just shake like it will spin but nothing. My question are these. Do these opt_fan headers make the fan spin only when the mobo needs it or when the mobo is hot enought to need the fan to spin? What is it that tells the header to turn the fan on? Is a low voltage issue when i set the opt_fan to user mode? Or is just no being need it by the mobo for the moment? Ty in advance.

[Analog]

Most Asus boards, especially the Z97 ones usually have thermal controlled fan profile, meaning that the fans will spin only when the computer (processor) hots a certain temperature threshold. You can reconfigure these settings from the BIOS.