This is the Exhaust vent cover to vent out air flowing through the hot-side of your AC (aka through the Intake and across the condenser coil). This exhaust vent cover is designed to keep moderately sized debris out of the ductwork. Exhaust air will blow out any dust or small debris. Keep this vent fully clear of obstructions to ensure proper AC operation. Use the trim ring to beautify the interior of the penetration.