What was found
DURING CLIMB AFTER TAKEOFF (MSP TO PHL) CABIN ALT CAUTION LIGHT ILLUMINATED. CREW OF FLIGHT 2473 FOLLOWED QRH PROCEDURES. PRESSURIZATION WOULD NOT RESET AND INOPERATIVE IN AUTO AND MANUAL MODES. THE CREW ELECTED TO DIVERT TO DAY WHERE THE AIRCRAFT MADE AN UNEVENTFUL LANDING. PSA MAINTENANCE TROUBLESHOT THE SYSTEM AND DETERMINED PRIMARY OUTFLOW VALVE FAULTY. DUE TO UNAVAILABILITY OF A SERVICEABLE OUTFLOW VALVE PRESSURIZATION SYSTEM DEFERRED IAW WITH MEL 21-32-01 CODE C. AIRCRAFT THEN RELEASED FOR SERVICE. UPON RECEIPT OF A SERVICEABLE OUTFLOW VALVE PSA MAINTENANCE REMOVED AND REPLACED THE PRIMARY OUTFLOW VALVE IAW CRJ 200 AMM. ALL OPERATIONAL TESTS GOOD. MEL CLEARED AND AIRCRAFT RELEASED FOR SERVICE.