As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OPERATION, THE AC WAS UNABLE TO MAINTAIN CABIN ALTITUDE BELOW 10000 FEET WITH ONE PACK OPERATION. AC RETURNED TO DEPARTURE, WHERE IT LANDED WITHOUT INCIDENT. POST FLIGHT INSP REVEALED LT ACM INOPERATIVE. REMOVED AND REPLACED LT ACM AND LT PACK SHUTOFF VALVE, OPS CHECK GOOD. NO OTHER DEFECTS NOTED. AC WAS RETURNED TO SERVICE