What was found
AT FL 400, DURING SLIGHT POWER REDUCTION FOR SPEED CHANGE, LT BLEED TRIP OFF LIGHT ILLUMINATED. PRESSURIZATION NORMAL. RESET OK. NR 1 N1 86.6, NR 1 N2 90.9. LEFT BLEED TRIP OFF, OCCURED AGAIN DURING INITIAL DESCENT, FL400. RESET OK AGAIN. ACCOMPLISHED NR 1 ENGINE HEALTH CHECK IAW T/C NG-36WC-00001. FOUND PRSOV STICKY & PRECOOLER CONTROL VALVE FAILED TO OPEN. REPLACED NR 1 ENGINE PRSOV IAW MM 36-11-04-400-801. REPLACED NR 1 ENGINE PRECOOLER CONTROL VALVE IAW MM 36-12-02-400-801. REPLACED NR 1 ENGINE PRECOOLER CONTROL VALVE SENSOR IAW MM 36-12-03-400-801. INSTALLATION TESTS PASSED. NO LEAKS. ACCOMPLISHED REPAIR CONFIRMATION FIM TASK 36-10 TASK 801, STEP J. OPS CKECKED GOOD.