As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB ACFT UNABLE TO HOLD PRESSURIZATION IN CABIN ALT CLIMBED WITH ALT. NEITHER AUTO OR MAIN MODE WAS ABLE TO CONTROL CABIN PRESSURIZATION. FOUND GND AIR CONDITION HOOK UP FLAPPER VLV STUCK IN THE FULL OPEN POSITION. CLEANED & LUBRICATED HINGE & SPRING. PERFORMED OPERATIONS CHECK PRESSURIZATION CONTROL SYS IN NORMAL MODE IAW AMM 21-22-04 & 21-31-00.