Why does air still blow through my vents when the car is turned off? on 2006 Pontiac G6

When I remove the keys & the car is no longer running sometimes the car will still blow air through the vents, not continuously but off & on.

Asked by for the 2006 Pontiac G6
GM has added relays to the blower motors of some models to prevent a mildew smell. The fan will blow for 3-5 minutes to dry the evaporator core when you shut the car off. It is normal.
I can go out to the car & get something a hour or two later & it is still sometimes blowing.