Air Condition fans is always on, even with the A/C controller off

Very common problem on Q45 and M30.  The fan blower motor is controlled by a component call  "Blower Amplifier" . When the amplifier goes bad shorts out the system making the blower motor work all the time. The only solution for the problem is to replaced the it.  The amplifier is located in the blower motor case and can be access by removing the glove box on the Q45 and under the blower case on M30.