What was found
WHILE CLIMBING THROUGH 14,000 FEET, RECEIVED EXCESS CABIN ALTITUDE WARNING. NO ECAM WARNINGS WERE PRESENT PRIOR TO WARNING. OXYGEN MASKS DEPLOYED AND CREW FOLLOWED COCKPIT OPERATING MANUAL PROCEDURES. WHILE SWITCHING TO MANUAL PRESSURIZATION, RECEIVED FIRST ABNORMAL CABIN PRESSURE READINGS ON ECAM CABIN PRESSURE PAGE. AIRCRAFT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE CABIN PRESSURE OUTFLOW VALVE 10HL, OPERATIONAL CHECK OK.