What was found
CLIMBING THRU FL 330 DISCOVERED SPLIT OF 23SPI. AT FL370 LEFT DUCT IS 43PSI RIGHT IS 21PSI. N1 AT 91 PERCENT N2 AT 94.4 SAT= 44C TAT= 16C. ENGINES ARE MATCHED PARAMETERS OTHER THAN DUCT PRESSURE. PRESSURIZATION NORMAL. DUCT PRESSURES CONVERGED TO SAME PRESSURE OF 42 PSI AFTER 1.5 HOURS. PERFORMED ENG BLEED AIR SYS HEATH CHECK & PRECOOLER CONT. VLV SYS HEATH CHECK REF MM 36 11 00 700 801 & 36 12 00 700 801. FOUND THE PRECOOLER CONTROL VALVE FAILING TEST G 14. REPLACED PRECOOLER CONT VLV REF MM 36 12 02 RE-ACCOMPLISHED PRECOOLER CONT VLV TEST & VLV NOW CHECKS GOOD. ENG BLEED AIR SYS, ALL CHECKS GOOD.