What was found
CABIN WOULD NOT PRESSURIZE AND CABIN ALT REMAINED AT 10,000 THROUGH OUT CLIMB. RESECURED ELECTRO PNEUMATIC VALVE CLOSED AS PER MEL 21-30-01, GROUND RUN SHOWS MANUAL CHECKS GOOD. FOUND LOOSE SECTION OF CARGO DOOR SEAL. PRESSURIZED ACFT TO 5.0 PSID IN AUTO AND MANUAL, OPS CHECKS GOOD. RESTORED ELECTRO PNEUMATIC VALVE TO NORMAL.