The MB specs do not mention fan controlls. The photo of MB show at least 2 fan connectors. I do not know this MB so can not help much.
fan with 2 wires just runs.
fan with 3 wires runs and reports fan speed on third wire.
fans with 4 wires are speed controlled by PWM, Pulse Width Modulation. They are not running on 12 Volts DC. They are running on 12 V that is turned on and off very fast to set speed. Some Bios have minimum setting for CPU fan speed that can be adjusted up.
If you want more speed, hook it to PSU 12V and it will run at Max RPM.
It sounds like your MB is working properly and is just slowing the fan down.