First of all when you are running AC you are putting pressure on your engine, so if it's cool outside why would you need to run AC when you can get a fresh air from outside?
Also, when you are running AC your miles per gallon go down. I personally get 3-4 gallons less when AC is running, so that's another reason not to have AC on when it is cool outside.
Rolling winodws down is a solution if you are on driving on the freeway
So it sounds like this system can only work as ac, not as ventilator that would blow outside temp air..