What was found
FLT#1463, LAX-SJD. (AIRCRAFT PERFORMED AN AIR TURN ABCK TO LAX) 'DURING CLIMB CABIN PR SYS 1 FAULT LEVELED AT 21000 DUETO STRONG PRESSURE FLUCTUATIONS. THE CABIN OUTFLOW VALVE OPENED AND CLOSED RAPIDLY. 2800-3100 CABIN ALT. VS CLMB AND 1000 / -1000 10 MIN AFTER SYS 1 FAULT ECAM SYS 1 AND 2 FAULT CABIN PRESSURE USED MANUL BACKUP FOR REMAINDER OF FLIGHT BACK TO LAX; REF LAST LEG REPORT FAULT CODE (81) PER TSM 21-31-00-810-828A. NO ICE OR WATER WAS FOUND. REMOVED AND REPLACED 19HL OUTFLOW VALVE PER AMM 21-31-51. PERFORMED CPC #1 & #2 BITE TEST, PASS. MANUAL MODE CHECK NORMAL.