What was found
FL390, IN CRUISE POWER SETTINGS, NR 1 AT 92.2, NR 2 AT 92.1 RIGHT PAC INDICATING 15 PSI LEFT PAC AT 37 PSI. PAC BELOW MN DUCT PRESSURE OF 18 PSI AND DIFFERENTIAL PRESSURE GREATER THAN 20 PSI AT FL 390 OAT 44C ISA DEVIATION PLUS 13 DEG C. CABIN ALT AT 7000. DIFFERENTIAL PRESSURE AT BASE YELLOW 8.4 PSID. ACFT GROUNDED. PRECOOLER CONTROL VALVE FAILED AMM QUICK FIM TASK 36-10-00-810-810, PARA F 5 C. REPLACED PRECOOLER CONTROL VALVE IAW AMM 36-12-02-000-801. PERFORMED REPAIR CONFIRMATION ENGINE RUN PER FIM 36-10-00-810-807, PARA G. CONFIRMATION SUCCESSFUL WITH ALL BLEED TARGETS ON TRACK WITH BOTH ENGINES.