What was found
-ATB- RETURNED TO MSP DUE TO PRESSURIZATION ISSUES. CORRECTIVE ACTION: MTC FOUND LOWER OVER PRESSURE RELIEF VALVE POPPED WITH INSULATION STICKING OUT. RESET PRESSURE RELIEF VALVES AND REPOSITIONED / SECURED INSULATION BLANKET. PERFORMED BITE OF BOTH CABIN PRESSURE CONTROLLERS, NO FAULTS NOTED. REPLACED LOWER POSITIVE RELIEF VALVE. PERFORMED EXCESSIVE CABIN PRESSURE LEAKAGE CHECK - PASSED. PERFORMED STEP 2 OF NEXT MAINTENANCE LAYOVER SINGLE PACK CONFIDENCE CHECK, CHECK PASSED. CABIN PRESSURE SELECTOR CHANGED ON LOG 3896248.