What was found
AFTER COMPLETION OF POSITIVE PRESSURE RELIEF VALVE TEST, AIRCRAFT WAS UNABLE TO HOLD CABIN ALTITUDE WITH A CABIN CLIMB OF APPROXIMATELY 600-700 FT PER MINUTE. ON POST FLT FOUND FOD IN UPPER POSITIVE PRESSURE RELIEF VALVE. INSULATION BLANKET FOUND JAMMED IN UPPER POSITIVE RELIEF VALVE. INSULATION BLANKET SHOULD NOT BE INSTALLED AT THIS LOCATION IAW DWG 757R2654-131-13. REMOVED INSULATION BLANKET IAW AMM 25-00-00. REPLACED UPPER POSITIVE RELIEF VALVE IAW AMM 21-32-01 CARRIED OUT CABIN PRESSURE LEAKAGE TEST IAW AMM 05-51-24.