As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF FROM MSP, THE FLIGHT EXPERIENCED A PRESSURIZATION PROBLEM AND CABIN ALTITUDE KEPT CLIMBING EVEN WITH ONLY ONE PACK OPERATING. RETURNED TO MSP DUE TO NOT ENOUGH FUEL ON BOARD TO CONTINUE TO DEN AT 10,000 FEET. *S/D* FOUND THAT NR 1 PACK DID NOT SEEM TO OPERATE IN FLIGHT. ALSO, LT MAIN ENTRY DOOR SEAL WAS OUT OF ITS RETAINER. SECURED SEAL AND REPLACE RT FLOW CONTROL MODULATING VALVE.