These cars have six fan speeds - check out the owner's manual.
The lower button is speed #1. The higher button is speed #6. If you push the narrow center divider between these two buttons, then both buttons are "out" or "disengaged" and the Automatic Climate Control computer decides which speed of #2 through #5 to give you. As the inside temperature gets closer to what you have the control dial set to, the fan will slow down more.
Hope this helps.