Air conditioner only works on full speed

2004 Jeep Wrangler SE 2.4L 4cyl 23,000 miles, My Jeep's air conditioner will only run on full speed. There are only 4 speeds and it will only kick on when the knob is turned to the fourth blower speed. When turned to a lower speed it's very quiet and barely dribbles out almost as if it's not even on. When on the highest speed the air is cold but it's much louder than usual. The sound seems to be coming through the vents and its like a loud hum. It seems to be condensating more too but I figured that was because it was always runing at full speed. Could it be the control in the dash?