What was found
FLT 776 - EN ROUTE TO BWI FROM LAS, UNABLE TO CONTROL CABIN PRESS AT FL 310. CABIN ALT CLIMBED TO 9500'. CREW DESCENDED TO LWR ALT AND EVENTUALLY STABILIZED CABIN. REPORTED BLEED PRESS AT 12 PSI. NR 2 PACK WAS DEFFERED WITH NR 1 PACK INTERMITTENT, FLUXING. DIVERTED TO PHX AND LANDED. MX REPLACED NUMEROUS SEALS IN LT PACK FROM ACM TO HEAT EXCHANGERS, HEAT EXCHANGERS TO RE-HEATER AND RE-HEATER TO CONDENSER. ALSO, FOUND POST FLT REPORT WAS FAULTING NR 1 ENG PRV (PRESS REG-V 4001HA1 OR SOL 10HA1 OR SENSE LINE). R&R NR 1 ENG PRV IAW AMM 36-11-52, LEAK AND OP TESTS NORMAL. ALSO, FOUND LT PACK ACM LEAKING AT MATING SURFACE. R&R NR 1 PACK ACM DUCT SEAL IAW AMM 21-52-21-400-002. LEAK CHECKS WERE GOOD.