As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL - FLT 1486 - CREW WAS UNABLE TO PRESSURIZE AIRCRAFT AFTER TAKEOFF. DUCT PRESSURE WAS GOOD AT 40 PSI AND OUTFLOW VALVE WAS FULL CLOSED. THE LEFT PACK WAS ON MEL. FLIGHT RETURNED TO FIELD AT PHL AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE FOUND THE RIGHT PACK WATER SEPARATOR BAG CLOGGED. REPLACED SAME. OPERATIONAL CHECK OF RIGHT PACK GOOD. (M)