What was found
CLIMBING OUT AND APPROACHING 10000 FT, NOTICED THE AIRCRAFT NOT PRESSURIZING. STARTED TO LEVEL OFF AND CABIN ALTITUDE LIGHT CAME ON WITH HORN. PERFORMED QRC AND SWITCHED TO MANUAL REGAINED CONTROL BELOW 10000 FT, MX DIRECTED TO ATTEMPT AUTO AND NO OUTFLOW VALVE MOVEMENT. WENT BACK TO MANUAL. ACFT GROUNDED. AIR TURNBACK. FOUND THE NR 2 AUTO PRESSURIZATION CONTROLLER HAD A FAULT CODE OF 029. NR 1 PRESSURIZATION CHECKED GOOD, RESET THE NR 2 AUTO PRESSURE CONTROLLER CIRCUIT BREAKER. PERFORMED SINGLE PACK OPERATION WITH APU PHASE III IAW AMM 21-00-05, NO FAULTS NOTED. PERFORMED A PRESSURE CONTROLLER BITE CHECK IAW FIM 21-31 TASK 801, NO FAULTS NOTED.