Thread: Erratic A/C fan?

I have a 2004 Grand Prix GTP. The A/C gets perfectly cold, but sometimes it doesn't blow any air. Strangely, when I hit the control panel next to the fan speed knob it starts blowing. However, this is only temporary and the fan speed is still erratic--it constantly slows down and speeds up without touching the knob. Does anyone know what could possibly be causing this? Thanks.