What was found
(CAN) PILOT REPORTED THAT THEY WERE HAVING CABIN PRESSURIZATION ISSUES, WHICH CAUSED THE UN-CONTROLLED DE-PRESSURIZATION. THIS CAUSED THEM TO INITIATE AN EMERGENCY DECENT. PRESSURIZATION SYSTEM WAS MEL`D ONCE ON THE GROUND AND THE AC FLEW UNPRESSURIZATION. WHEN IT GOT TO HOME BASE MAINTENANCE FOUND MOISTURE IN THE AIR-STAIR DOOR SEAL LINE, WHICH WAS REMOVED AND ADJUSTED. THE CABIN DOOR AIR SWITCH AND SUBSEQUENT FLIGHT TEST COMPLETED OK. (TC# 20180822009)