How do you replace the heater core on 1999 deville cadllac?

To replace the heater core on a 1999 Cadillac DeVille, first disconnect the battery and drain the coolant. Remove the dashboard and the center console to access the heater core housing, then disconnect any attached hoses and electrical connectors. Remove the heater core from its housing, install the new heater core, and reassemble everything in reverse order, ensuring all connections are secure and the system is properly refilled with coolant. Finally, check for leaks and ensure the heating system operates correctly.