What was found
AT START OF DESCENT INTO PKWA PRESSURIZATION CONTROL LEVER AND OUTFLOW VALVE FROZE UP. THE CREW HAD TO DO AN EMERGENCY DESCENT, THE O2 MASK IN CABIN DROPPED WHEN ALT INCREASED TO 15000 FT. THE CREW LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE IN PKWA DEFERRED PRESSURIZATION TO PHIK IAW MEL 21-10-01. MAINTENANCE IN PHIK REPLACED CABIN RATE CONTROLLER, OUTFLOW ACTUATOR. OPERATIONAL CHECK GOOD IAW MM 21-31-2, 21-31-0, 21-31-4, AND 21-31-4. ACFT WAS RETURNED TO SERVICE.