What was found
ON CLIMB OUT, AUTO PRESSURIZATION FAILED, CABIN PRESSURE CLIMBED QUICKLY, NO FAILURE LIGHT INDICATED. STABILIZED PRESSURIZATION IN STANDBY THEN RESELECTED AUTO, PRESSURIZATION WAS OK AT FIRST, BUT THEN FAILED AGAIN, STILL NO WARNING LIGHT. OUTFLOW VALVE INDICATED CLOSED, STABILIZED PRESSURIZATION IN STANDBY AT 12000 ALTITUDE AND ABLE TO CONTROL PRESSURIZATION SCHEDULE MANUALLY, TURNED BACK & LANDED WITHOUT EVENT. MAINT FOUND CIRCUIT BREAKER POPPED, R & R CABIN PRESSURE CONTROLLER, RESET CIRCUIT BREAKER, AND PERFORMED CABIN SAFETY PRESSURE AND RELIEF VALVE TEST IAW T/C F1B21001, TEST WAS GOOD. FUNCTIONAL CHECK OF CABIN PRESSURE CONTROLLER S/N FD37127 CONFIRMED FAILURE OF UNIT.