What was found
MSN TO CVG - WHILE CLIMBING THROUGH 13,000 FT, THE CREW RECEIVED A CABIN ALTITUDE RED MESSAGE CABIN ALTITUDE 10,000 ALONG WITH A WARNING MESSAGE. THE CREW LEVELED OFF AT 15,000 FT THEN STARTED TO DESCEND. WHILE DESCENDING THE CABIN PRESSURE BECAME AMBER THEN GREEN AGAIN. THE AIRCRAFT LANDED BACK AT MSN UNEVENTFULLY. MAINTENANCE DEFERRED BOTH OUTFLOW VALVES AND THE AIRCRAFT WAS FERRIED UNPRESSURIZED TO CVG. ONCE IN CVG MAINTENANCE TROUBLESHOT THE FAULT DOWN TO THE PRESSURE CONTROLLER, AND AFTER REPLACING IT, THE PRESSURIZATION SYSTEM OPERATED NORMALLY.