When the AC is switched"OFF", and the blower is blowing air. A foul smell comes out of the AC system. The exact reason is not known but as we know that all kinds of cost cutting has been done and if the poor quality ducting is exposed to heat it can release fumes in the AC duct , which produce this foul smell.

If this is so,we always have the windows closed during AC and these fumes from bad quality plastic can cause cancer for the driver and passenger inside the car.