As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF FROM RJTY, THE AIRCRAFT WOULD NOT PRESSURIZE. THE CREW RETURNED TO RJYT AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIRCRAFT AIR-CONDITIONING PACK SYSTEM AND PERFORMED AN OPERATIONAL CHECK OF THE AIRCRAFT PACK SYSTEM. THE AIRCRAFT SUCCESSFULLY PRESSURIZED DURING THE OPERATIONAL CHECK AND THE AIRCRAFT WAS RETURNED TO SERVICE.