While Driving, the inside Fan and climate unit.

While Driving, the inside Fan and climate unit turned on at full blast, also noticed it seemed to turn on A/C - the buttons seem not to control functions but the A/C button has a light and it does go on and off when I press it, the fan control button also seems to work because it shows the levels of blower speed, but unit just is stuck on "ON" and blowing at full blast with A/C on, now I can not shut it down, turn car off all turns off, turn car on and unit comes on at full blast, I know that if a fuse blows the unit should react as to not turn on, but what the heck is wrong with it when it won't shut down. What in the world causes the reverse action and How do I fix it. A Fuse? Because I did not hit a bump or anything I was on Highway with all shut off and air vents open to accept outside air and no fan on, then pow it turned on at full blast.