What was found
MAIN CABIN DOOR ACOUSTIC SEAL WILL NOT RELEASE AFTER SHORT FLIGHT WITH SERVICE AIR ON. DOOR CANNOT BE OPENED WHILE APU WAS RUNNING. HAD TO SHUT DOWN APU TO REMOVE SERVICE AIR BEFORE WE COULD EXIT. REMOVED CABIN ENTRY DOOR STEPS AND INSPECTED PRIMARY DOOR SEAL VALVE WITH NO DEFECTS NOTED AND OPS CHECKS GOOD. INSTALLED CABIN ENTRY DOOR STEPS REF. CESSNA 560XL MM 52-10-02. GAINED ACCESS TO ACCOUSTIC DOOR SEAL VALVE AND INSPECTED WITH NO DEFECTS NOTED. ADJUSTED ACCOUSTIC DOOR SEAL VALVE REF. CESSNA 560XL MM 36-15-00. OPS CHECKS GOOD.