What was found
DUCT PRESSURE INFLIGHT READ: LEFT 38 PSI, RIGHT 12 PSI AT CLIMB AND CRUISE CRUISED AT FL350, N1 85%. STAYED AT 12 PSI (RIGHT) AT IDLE POWER. LEFT PSI DROPPED TO 12 AT IDLE. RIGHT REMAINED AT 12 PSI THROUGH APPROACH AND LANDING. GROUNDED-YES. REMOVED AND REPLACED PRSOV DUE OBSERVED LEAK, REF B737-900 AMM 36-11-04. REMOVED AND REPLACED BLEED AIR REGULATOR, PER AMM 36-11-03-400-801. PERFORMED T/C NG-36WC-00001. NO DEFECTS NOTED BLEED AIR PSI WITHIN LIMITS FROM IDLE TO 80%, REF AMM 36-11-00-710-801. FOUND BLEED AIR REG C/B OUT P4 B7. RESET REF AMM 20-60-01-860-801.