As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ACFT FAILED TO PRESSURIZE EVENLY; ALT WARNING HORN SOUNDED AND MASKED FELL AS WE CLIMBED THOUGH FL200. AFTER EMERGENCY DESCENT, APU WAS REENGAGED BUT EVEN THEN ALT WARNING HORN STAYED ON UNTIL BELOW 8000FT; AND BOTH CREW CONFIRMED ONGOING PRESSURE FLUCTUATIONS. R & R UPPER AND LOWER CABIN PRESSURE CHECK VALVES IAW MM 21-30-00. PERFORMED GROUND PRESSURIZATION CHECKS. OPS CHECKED GOOD.