from what i read the auto will adjust the fans and ducts until the desired temp is reached, so for example if its set to 66 and the auto believes the best way to obtain that temp is to use max ac which recirculates the air in the car it will do so.
try turn the auto temp up till 72 then hit max ac do this once the car is cool and you will here the blower ducts move and fan increase in sound
try turn the auto temp up till 72 then hit max ac do this once the car is cool and you will here the blower ducts move and fan increase in sound