What was found
AIRCRAFT N464AT DEPARTED EWN FOR ISO WITH THE LEFT HAND AIR CONDITIONING PACK AIRFLOW SHUTOFF VALVE ON DMI (MEL 21-02) AND FLYING UNDER PACK PRESSURIZED OPERATIONS PROCEDURE. EN ROUTE TO ISO AT A FL OF 22,000 FEET THE FLIGHT CREW NOTICED THE RIGHT HAND AIR CONDITIONING PACK WAS HAVING DIFFICULTY MAINTAINING CABIN PRESSURE. THE FLIGHT CREW DECIDED TO DESCEND TO A LOWER ALTITUDE, AT APPROXIMATELY 16,000 FEET THE RIGHT HAND AIR CONDITIONING PACK TRIPPED THE C/B AND CAUSED THE PSU OXYGEN MASK TO DROP. FLIGHT WAS DIVERTED TO GSO.