As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO PRESSURIZE THE CABIN. FLIGHT RETURNED TO FIELD. THIS AIRCRAFT HAD A SIMILAR PROBLEM ON 10/24/02. THE GROUND EQUIPMENT COOLING EXHAUST VALVE FAILED OPEN. THE VALVE WAS FOUND TO HAVE WORN BEARINGS AND INTERNAL PARTS CAUSING INTERMITTENT OPERATION.