I see in the mobo manual that all the fan headers are labelled solely as "Fan1", etc. However, the manual also indicates that, in BIOS Setup, there are separate settings available for the CPU FAN and the SYS FANs. I suggest you plug your CPU cooler into FAN1. Then go into BIOS Setup and try setting CPU_FAN to one of the fixed slower speeds. You may have to SAVE and Exit from BIOS Setup to see the fan speed change. Try this process with other speed settings on CPU_FAN. If this does NOT change the CPU cooler speed, then try again using a different header, until you can identify the one that the CPU_FAN settings work on.