What was found
LEFT BLEED TRIP OFF ILLUMINATED AFTER CLIMB TO FL 410, LT PACK PRESSURE DROPPED TO 0. RESET AND HAD NORMAL OPERATION FOR 5 MIN AND THEN CONDITION REASSERTED. DESCENDED TO FL 390 AND RESET, OPS NORMAL. ACFT GROUNDED. PERFORMED ENGINE BLEED AIR SYS HEALTH CHECK TC NG-36WC-00001. FOUND HIGH STAGE VALVE AND PRE-COOLER VALVE BAD. REPLACED HIGH STAGE VALVE AND PRE-COOLER VALVE IAW MM 36-11-06-000-801, 36-11-06-400-801, 36-12-02-400-801, 36-12-02-000-801. LEAK CHECK GOOD. PERFORMED HIGH POWER RUN IAW FIM 36-10 TASK 801, STEP J15. GROUND VERIFICATION SUCCESSFUL NOTE ALL WORK DONE ON NR 1 ENGINE.