What was found
PDIS 922 21-30 3695 07DEC22 CDG FACT U RECEIVED CABIN ALT WARNING IN FLIGHT AT FL400. CABIN ALT WAS JUST OVER 10,000 . DIFFERENTIAL PRESSURE WAS APPROXIMATELY 7PSI. WE DESCENDED TO 10,000 . EXECUTED THE QRC/QRH. WE KEPT THE CABIN ALTITUDE CONTROL IN AUTO. IT FUNCTIONED NORMALLY AFTER THAT. R/I 08DEC22 01:47 CDG U REASON CODE : PREMATURE REMOVAL/INSTALLATION OFF MPN: 5669-18 POS: ONL SRL: 5487 ON MPN: 5669-18 CPN: 2112858 SRL: 5466 TAG NBR: I34563 AMM: 21-58-05-4 AMM: 05-51-24-2 CABIN PRESSURIZATION LEAKAGE TEST PERFORMED IAW AMM 05-51-24-2, FOUND EQUIPMENT COOLING OVERBOARD EXHAUST VALVE STUCK IN OPEN POSITION, UNABLE TO REACH THE FULLY CLOSED POSITION. REMOVED AND REPLACED VALVE IAW AMM 21-58-05-4, VALVE OPERATES PROPERLY AND PERFORMED PRESSURIZATION LEAKAGE TEST AGAIN, FOUND SATIS.