What was found
APPROX 5 MIN AFTER T/O, THE FWD CARGO HOT LIGHT ILLUMINATED. SHORTLY AFTERWARD A POPPING NOISE BEGAN EMANATING FROM RT SIDE OF A/C JUST AFT OF F/C. AFTER LEVEL OFF AT FL 310 TROUBLESHOT BY TURNING ONE PACK OFF AT A TIME, UNABLE TO MAINTAIN PRESSURIZATION WITH 2 PACKS OPERATING AT FL 310. RETURNED TO SJU FOR MTC. FOUND C-1 DOOR FWD UPPER SEAL MISSING. INSTALLED NEW SEAL AND PRESSURIZED A/C PER MM 21-31-00 PG 508, CKD OK.