What was found
CMH - FLT 250 - CMH/PHL - AIRCRAFT WOULD NOT PRESSURIZE, AUTO FAIL LIGHT ILLUMINATED. CREW COULD NOT CLOSE OUTFLOW VALVE IN ANY MODE. AIRCRAFT RETURNED TO CMH AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REMOVED AND REPLACED THE NR 1 PACK AIR MIX VALVE, NR 1 PACK SENSE LINE, NR 2 AIR CYCLE MACHINE, AND THE NR 2 PACK AIR MIX VALVE DUCT. AIRCRAFT PRESSURIZED ON GROUND PER BMM 05-51-91, PAGE 202. AIRCRAFT RETURNED TO SERVICE. REFERENCE AWXA9500762.