Engine coolant moves from the engine to the heater system's core through the heater and evaporator module to heat the air you breathe. The heater core has two holes for the coolant to enter and leave, which means you must put the hoses in just the right place before you take it apart for service. To replace the heater core in Eldorado and Seville models, begin by taking off the car's negative battery terminal and emptying the engine's coolant. Take off the glove box unit and right side lower sound insulator, then disconnect the programmer-unfasten screws, detach electrical wires, and remove the vacuum hose connector. In old models, disconnect electrical connectors and take off mounting supports before starting work. You will remove the heater core by unclipping the cooler attachment points and unscrewing it once you remove the protective cover and disconnect all heat tube connections. To reinstall, screw the heater core in place, put the hoses back on, and put the cover back on. Put back the PCM and BCM, making sure each of them snaps into their plug. Reconnect both the original programmer and negative battery terminal, while checking all mounting parts remain tight. Complete the job by first setting the temperature on the air mix valve, then checking if it moves without force, adjusting the valve with preload, making sure movement is correct, and then reinstalling the soundproofing and glove box.