What was found
DURING CLIMB, THE FLIGHT CREW REPORTED THAT THE CABIN ALTITUDE WAS CLIMBING ABNORMALLY IN AUTO MODE. THE AIRCRAFT RETURNED TO CLE AND LANDED WITHOUT INCIDENT. MAINTENANCE OPS CHECKED THE MANUAL PRESSURIZATION SYSTEM WITH NO DEFECTS NOTED AND PLACED THE AUTO PRESSURIZATION SYSTEM ON MEL AND RELEASED THE AIRCRAFT. AFTER THE NEXT FLIGHT FROM CLE TO PHL THE FLIGHT CREW AGAIN REPORTED THAT THE CABIN ALTITUDE WAS CLIMBING ABNORMALLY. AFTER FURTHER INSPECTION THE GROUND AIR CONNECTION CHECK VALVE WAS FOUND TO BE DAMAGED AND LEAKING. THE VALVE WAS PLACED ON MEL AND THE AIRCRAFT CONTINUED WITHOUT INCIDENT. DURING OVERNIGHT MAINTENANCE IN CMH, THE GROUND AIR CONNECTION CHECK VALVE WAS REPLACED WITH NO FURTHER DEFECTS NOTED.