As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE CLIMBING OUT, CREW REPORTED LEFT ENGINE PACK VALVE CLOSED. CREW COULD NOT GET VALVE TO OPEN. RIGHT PACK WAS ALREADY ON DEFERRAL PER MEL. CREW RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED, REMOVED AND REPLACED LEFT PRSOV (PRESSURE REGULATING / SHUTOFF VALVE) FILTER AND PERFORMED CHECKS USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT RELEASED FOR SERVICE.