As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN PRESSURE ANNUNCIATOR ILLUMINATED PASSING 10,000 FT MSL. UNABLE TO PRESSURIZE AIRCRAFT MANUALLY OR WITH AUTOMATIC CONTROLLER. VISUALLY INSPECTED AIRCRAFT, NO DEFECTS NOTED. FOUND GROUND AIR CONDITIONING CHECK VALVE NOT SEATED. MANUALLY CYCLED CHECK VALVE FLAPPER IAW DC9 AMM 21-20-04. AIRCRAFT PRESSURIZES NORMALLY ON THE GROUND.