What was found
(CAN) ON CLIMB, THE LT OUTFLOW VALVE STICKING THROUGH 22,000 FEET, UNABLE TO MAINTAIN CABIN ALTITUDE, AIRCRAFT RETURNED. WITH MODE SELECTOR SWITCH IN MANUAL, PRESSURIZATION WAS FLUCTUATING THROUGH 10,000 FEET IN CLIMB, ABLE TO OPERATE BOTH OUTFLOW VALVES NORMALLY. CHANGED LT OUTFLOW VALVE ACTUATOR AND PRESSURE CONTROLLER, SYSTEM TESTED OK.