I pulled my AC years ago. I was looking at my stock fans, and one is super dirty, and lots of dead bugs junk on it I would think would fling off if it was spinning still. Other fan dosn't have any dust on it and alot cleaner. When dose the other fan kick on< I think it was only when the car was stopped or going under 40mph or somthing, But you have the AC on for it to kick on?