It's normal. It's called afterblow. There is a timer circuit built in to the climate control. Any time the A/C has been used for more than 5 minutes, the timer will activate the blower fan for five minutes aprox 50 minutes after shuting off engine to dry out the evaporator and prevent mold and mildew. Turning the key on/off while it's running will shut it off. This function can be deactivated by your dealer if undesired.