As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - LAS - EL - NR 7752072 - CREW REPORTED DURING CLIMB-OUT, PACK NR 2 TRIPPED OFF AND WOULD NOT RESET. THE NR 1 PACK WAS ON MEL. THE CREW DECLARED AN EMERGENCY AND RETURNED TO PHX. REMOVED AND REPLACED PLENUM PER AMM 21-52-22, PACK OPERATIONAL CHECK WAS GOOD.