What was found
IN CLIMB OUT, LEFT DUCT PRESSURE READS 43 AND RIGHT DUCT PRESSURE READS 20. DURING CRUISE, FL 370 BOTH READ 43. BOTH PACKS AUTO, BOTH BLEEDS ON, ANTI-ICE OFF. ACCOMPLISHED T/C NG-36WC-00001 FOUND PRECOOLER CONTROL VALVE FAILED. REMOVED AND REPLACED PRECOOLER CONTROL VALVE IAW MM 36-12-02-000-801 AND 36-12-02-400-801. ACCOMPLISHED BLEED AIR OPS TEST & REPAIR CONFIRMATION REF MM 36-11-00-710-801 & FIM 36-10-00-810-807. NO DUCT SPLIT NOTED - DUCT PRESSURE WITHIN CHART LIMIT.