2001 Taurus A/C stuck on? (engine code U)

It seems that the A/C compressor on my '01 Taurus is stuck on. The system blows very cold air even when the selector knob is set to vent. Any ideas how what steps to take to diagnose the problem?

Not sure about diagnosing the problem, but it was happening to me also. Eventually I switched to Off; the selector for a little bit,and this might reset the selector back to normal like :vent.