As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO PRESSURIZE CABIN, DUMPED APPROXIMATELY 30,000 POUNDS OF FUEL AND RETURNED TO LAS. FOUND CHECK VALVE (P/N 7012-505) TO BE INOP IN NUMBER 2 PACK AND A BLOWN AIR CONDITIONING DUCT (P/N 7009-605). REMOVED AND REPLACED BOTH PARTS IAW MM 21-30-0. DUCT LEAK AND CHECK VALVE OPERATIONAL CHECKS WERE PERFORMED.