What was found
LAX FLIGHT NR 2420: CABIN WOULD NOT PRESSURIZE. DIFFERENTIAL OF 0.2 PSI MAX WAS ACHIEVED WITH BLEED MAX. EMERGENCY CHECKLIST NO HELP. MAINTENANCE INSPECTED AND FOUND AFT CARGO DOOR SEAL WOULD NOT INFLATE DUE TO AFT CARGO DOOR SEAL CONTROL VALVE WAS STICKING AND NOT ALLOWING SEAL TO INFLATE. REMOVED AND REPLACED AFT CARGO DOOR SEAL CONTROL VALVE IAW Q400 AMM TASK 52-31-31-000-801 AND 52-31-31-400-801. PRESSURIZED AIRCRAFT IAW Q400 AMM TASK 21-00-00-863-801 AND 21-00-00-863-802. OPS CHECK GOOD. NO LEAKS NOTED. AIRCRAFT RETURNED TO SERVICE.