What was found
CLT FLT 806 EN ROUTE CUN TO PHL. THE FLIGHT DEPARTED CUN WITH THE LEFT AIR CONDITIONING PACK ON MEL. DURING CRUISE, THE CREW STATES: "COULD NOT HOLD PRESSURIZATION IN AUTO, WENT TO MANUAL. ALSO COULD NOT CONTROL UNTIL FL 7000. L&R DUCT PRESSURE 40-50 PSI." THE FLIGHT DECLARED AN EMERGENCY, DESCENDED QUICKLY TO FL 170, AND THEN DIVERTED INTO CLT. MAINTENANCE FOUND DUCT COUPLING OFF RT PACK. REPLACED COUPLING & CLAMPS. LEAK CHECKED, NO LEAKS NOTED. ACCOMPLISHED EXCESSIVE CABIN PRESSURE LEAK TEST. CHECK'S GOOD. OK FOR SERVICE.