What was found
AT 20,000 FEET NR 1 PACK VALVE LIGHT CAME ON, FLIGHT CREW TRIED TO RESET COULD NOT. THE RECIRCULATION VALVE WENT FREST COULD NOT RESET. NR 2 PACK VALVE LIGHT CAME ON, LOST PRESSURE. RESTORED CABIN PRESSURE AT 10,000 FEET PACK WORKED. MAINTENANCE PRESSURIZED A/C TO MAX DIFF, ON APU AIR AND ENGINE AIR LEAK CHECKED AT PACKS AT MAX DIFF GOOD, NO LEAKS NOTED. BOTH PACKS OPERATE NORMAL ON GROUND CHECKS, TEST FLIGHT SATISFACTORY.