As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT DEPRESSURIZED WHILE AT 6000 FEET, OUTFLOW VALVE WAS FULL CLOSED. THE AIR CONDITIONING SUPPLY SWITCHES WERE ON AND PRESSURIZATION WAS SET FOR LANDING. PRESSURIZED AIRCRAFT TO MAXIMUM DIFFERENTIAL PRESSURE WITH NO PROBLEMS NOTED. INSPECTED LINKAGE TO/FROM THE OUTFLOW VALVE AND ACTUATOR, NO DEFECTS NOTED. CHECKED FOR PRESSURIZATION LEAKS, NONE FOUND.