What was found
AIRPLANE WOULD NOT PRESSURIZE AFTER TAKEOFF IN AUTO OR MANUAL MODE. RETURNED TO FIELD. LANDING UNEVENTFUL. INSPECTED AND FOUND AFT CARGO BAY BLOW-OUT PANEL DISLODGED. REINSTALLED BLOW-OUT PANEL IAW AMM TASK 25-52-01-400-802. FOUND AFT CARGO DOOR SEAL NOT INFLATING. C/W GVI OF SEAL WITH NO DEFECTS NOTED. APPLIED HEAT TO AFT CARGO DOOR AND THAWED FROZEN DOOR SEAL. DOOR SEAL NOW INFLATES NORMALLY. C/W PRESSURIZATION IAW AMM TASK 21-00-00-863-801, A/C PRESSURIZES NORMALLY. RETURNED TO SERVICE. NO PARTS REPLACED.