As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5980, DURING CLIMB, FLIGHT CREW WAS UNABLE TO GET THE AC TO PRESSURIZE USING EITHER MANUAL OR AUTO PRESSURIZATION MODES. FLIGHT RETURNED TO DEPARTURE AND LANDED WITHOUT INCIDENT. THE PRESSURIZATION SYS WAS PLACED ON MEL AND THE AC RESUMED FLYING UNTIL THE MEL WS CLEARED ON THE 7TH. MAINT FOUND THE VACUUM LINE (P/N: 123-07692-407) LEAKING AND REPLACED IT. MANUAL PRESSURIZATION CONTROLLER WAS ALSO FOUND TO BE NOT CONTROLLING PRESSURIZATION AND IT WAS REPLACED. (A)