As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PRESSURIZATION FAILED DURING CLIMBOUT. INOP IN MANUAL MODE, ''CABIN ALT'' CAUTION MSG PASSING 13,500 FT MSL. UNABLE TO RESTORE PRESSURATION. RETURNED TO CPR. FOUND LOW PRESSURE EXTERNAL AIR SUPPLY CHECK VALVE STUCK OPEN. CLEANED AND INSPECTED CHECK VALVE, PRESSURIZED AIRCRAFT. ALL CHECK NORMAL.