How do you replace the heater core on a 1994 Cadillac DeVille?

To replace the heater core on a 1994 Cadillac DeVille, start by disconnecting the negative battery cable and draining the coolant. Remove the dashboard and the HVAC assembly to access the heater core, which is typically located behind the firewall. Disconnect the heater hoses from the core, remove the mounting bolts, and take out the old heater core. Install the new core by reversing the process, ensuring all connections are secure and refilling the coolant before testing the system.