What was found
(CAN) THE CREW NOTICED AN UNCONTROLABLE OVER PRESSURIZATION IN CRUISE. THEY SET THE SYS TO MANUAL MODE TO CONTROL BUT MANUAL MODE DID NOT WORK ALSO. THEY BEGAN TO DESCEND AND HAD TO SHUTOFF ALL ENGINE BLEED AIR WHICH WOULD ALLOW THE CABIN TO START TO DESCEND. THEY LANDED WITH NO ISSUES. AFTER CONSULTING WITH MFG, WE FOUND THE CABIN VENT VALVE FAILED IN THE CLOSED POSITION. THE VALVE WAS REPLACED AND SATISFACTORY TESTS WERE CARRIED OUT. MFG HAS FLAGGED THIS FAILED VALVE FOR A COMPLETE INSPECTION OF THE VALVE TO SEE WHAT WAS THE CAUSE.