As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) FLIGHT CREW INFORMED MX THAT THE ACFT WAS PRESSURIZING ON THE GROUND. MX FOUND THE VACUUM LINE TO THE OUTFLOW VALVE WAS MELTED. AN INVESTIGATION INTO THE CAUSE OF THE MELTED TUBE FOUND TO BE AN AIR PLENUM ASSY, DEFLECTOR HAD BECOME SEPARATED AND ALLOWED HOT AIR TO BE DEFLECTED AT THE PRESSURIZATION CONTROLLER LINE. MX REATTACHED THE DEFLECTOR AND REPLACED THE CONTROLLER LINE.