What was found
IAH - FLT 887 - AIR TURNBACK, IAH TO PHX, AFTER TAKEOFF, CREW REPORTED THAT THEY WERE UNABLE TO PRESSURIZE THE AIRCRAFT IN ANY MODE. BOTH OUTFLOW VALVES SHOWED FULL CLOSED AND THE PNEUMATIC DUCT PRESSURE WAS NORMAL. CONTRACT MAINTENANCE INSPECTED THE AIRCRAFT DOOR SEAL AND FOUND NO DEFECTS. PRESSURIZED THE AIRCRAFT WITH FIRST THE APU, THEN THE ENGINES. OPERATIONAL CHECKS WERE NORMAL. AIRCRAFT WAS RELEASED FOR SERVICE WITH NO FURTHER PROBLEMS. INBOUND CREW REPORTED NO FAULTS AND THE AIRCRAFT REMAINS IN SERVICE. (W)