What was found
INSPECTION TYPE: NA ATB, NO EMERGENCY DECLARED. CABIN INFLOW LOW LEVEL 1 ALERT ON DURING CLIMBOUT. FOLLOWED CABIN ALTITUDE CHECKLIST AND MONITORED ILLEG CONTINUED TO CLIMB OUTFLOW VALVE WAS FULL CLOSED. CABIN ALTITUDE COULD NOT BE MAINTAINED. RETURNED TO SDF. RECEIVED AVIONICS FLO OVERIDE 101 ADJUSTED CABIN PRESSURE OUTFLOW VALVE ACTUATOR PUSH ROB ASSEMBLY, IAW MM 21-31-20-400-801. PERFORMED FUNCTIONAL TEST OF CABIN PRESS CONTROL SYSTEM, IAW MM 21-31-00-700-801, ALL OPERATIONS NROMAL.