Air Fan Broken for 2000 S80?

[aw]

The air conditioning works fine but the problem is that the air being sent out of the vents is leaving at a mininum. By turning the knob to increase fan speed nothing happens. This leads me to belive its a broken regulator but I'm not sure. If anyone knows how to solve such a problem or a way to open up to see the air fan please let me know. Thanks ahead of time.