As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF WITH THE RT PACK DEFFERED, THE CREW REPORTED CABIN PRESSURIZATION WAS INOPERATIVE IN AUTO AND MANUAL MODES. THE FLIGHT RETURNED TO CAK AND LANDED WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE LT PACK PRESSURE REGULATING SHUTOFF VALVE. THE PRESSURIZATION SYSTEM OPERATIONALLY CHECKED GOOD. THE AIRCRAFT WAS RELEASED FOR SERVICE.