What was found
AIRCRAFT WOULD NOT MAINTAIN PRESSURIZATION AT FL310. CABIN ALTITUDE CONTINUED TO CLIMB 150 TO 300 FPM AT CRUISE. CARGO HEAT OUTFLOW VALVE CLOSED AND CABIN RATE INCREASED TO 1500 FPM UNCONTROLLABLY. AIRCRAFT DESCENDED FROM FL310 TO FL240, CABIN PRESSURE BEGAN TO RESPOND BELOW FL290, FLIGHT CONTINUED AT FL240, PRESSURIZATION CONTROL MANUAL. TRANSFERRED TO DMI LIST NR 88109098 IAW MEL 21-16-1A, PLACARDS INSTALLED. AUTO CONTROL IS WORKING FINE AFTER MAIN CARGO DOOR SILL REPAIR. CLEARED DMI NR 88109098 AUTO PRESSURIZATION PER FLT CREW INFORMATION ON PRESSURIZATION SATISFACTORY.