What was found
DURING CLIMB FROM FL 360 TO 370 A DUCT PRESSURE SHOWED 23 PSI DIFFERENCE. LEFT DUCT 27 PSI, RIGHT DUCT 50 PSI. AT CRUISE FL 370 DUCT PRESSURE SHOWED 7 PSI DIFFERENCE, LEFT DUCT 35 PSI, RIGHT DUCT 42 PSI. ACFT GROUNDED. PRECOOLER CONTROL VALVE FAILED HEALTH CHECK IAW TASK CARD NG-36WC-00002-1. REMOVED AND REPLACED PCCV, IAW AMM 36-12-02-000-801, AMM 36-12-02-400-801. HIGH STAGE REGULATOR FAILED HEALTH CHECK IAW TASK CARD NG-36-WC-00002-1. REMOVED AND REPLACED HSR, IAW AMM 36-11-07-000-801, AMM 36-11-07-400-801. THE NEW HSR FAILED HEATLH CHECK IAW STEP Q(2)F. ACCOMPLISHED NR 1 ENGINE BLEED AIR SYSTEM HEALTH CHECK IAW T/C NG-36WC-00001. HSR PASSED HEALTH CHECK, ALL OTHER SYSTEMS TEST OK. ACCOMPLISHED NR 1 ENGINE BLEED AIR CROSSOVER OPERATIONAL TEST, TESTED GOOD. ALL PRESSURES WITHIN NORMAL OPERATING RANGE.