If the crack is in your ceiling hot air in the attic can draw/suck cold conditioned air out. It happens through a natural principle of science call convection.
Net free venting requirements for residential construction states that we should provide a “balanced” air flow for attic ventilation. 50% of the air needed to cool your attic should enter at the edge of the roof…down near the windows. 50% of the required openings should be as high as