As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX - CREW REPORTED, UNABLE TO PRESSURIZE AIRCRAFT IN AUTO MANUAL MODE AFTER DEPARTURE. AIRCRAFT RETURNED TO STATION WITHOUT INCIDENT. MAINTENANCE CLEANED DIFFERENTIAL FILTER ON EMERGENCY SAFETY 'DUMP' VALVE. PRESSURIZATION SYSTEM OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE. (M)