What was found
ON CLIMB OUT, THE LT AND RT DUCT PRESSURE HAD A SPLIT OF APPROXIMATELY 20 PSI. THE SPLIT REDUCED TO ABOUT 8 PSI AT TOP OF CLIMB. AFTER LEVEL AT 350 THE LT DUCT READ 40 AND THE RT DUCT WAS 37 PSI. NOTE CLIMB PRESSURES LT 17, RT SIDE WAS 38 PSI. ACFT GROUNDED. ACCOMPLISHED NR 1 ENG BLEED AIR SYS HEALTH CHECK REF T/C NG-36WC-00001. PRECOOLER CONT VALVE FAILS - CLOSES TOO SOON. NO OTHER DEFECTS FOUND ON HEALTH CHECK T/C. REPLACED NR 1 ENG PRECOOLER CONT VALVE REF MM 36-12-02-000-801 & -400-801. ACCOMPLISHED BLEED AIR OPS TEST & REPAIR CONFIRMATION REF MM 36-11-00-710-801 & FIM 36-10-00-810-807. NO OPS DEFECTS NOTED.