What was found
CAPTAIN REPORTED THAT DURING DESCENT AT 10,000 FEET, BOTH LT AND RT AIR CONDITIONING SYS SHUTDOWN WITHOUT APPARENTLY CAUSE, AIRCRAFT WAS DEPRESSURIZED, BUT OXYGEN MASKS DID NOT ACTIVATE. BOTH PRESSURE CONTROLLERS WERE RESEATED, AIR CONDITIONING SYSTEMS WERE CHECKED BY LEAKS, AND ENGINES WERE RUN, PRESSURIZING AT 7 POUNDS OF DIFFERENTIAL PRESSURE. AIRCRAFT WAS REFUELED AND DISPATCHED AT FL 250. DURING OVERNIGHT CHECK AT MEX, BOTH AIR CONDITIONING SYSTEMS, REGULATOR VALVE, FLOW CONTROL VALVE, COOLING TURBINES, CHIP DETECTORS AND TEMPERATURE CONTROL VALVE WERE CHECKED, DETECTING A PNEUMATIC LEAK IN SENSOR LINE NR 1, SO BOTH SECOND SEGMENT SWITCHES WERE REPLACED AND TESTED IAW MM 21-31-09, NO LEAKS WERE FOUND.