To remove the heater core in a 1999 Deville, start by disconnecting the cable from the negative terminal of the battery and draining the cooling system. The heater core is located in the passenger compartment, under the instrument panel. Disconnect the heater hoses at the firewall and remove the instrument panel to access the heater core cover. Disconnect the rod from the programmer to the blend-air door and disconnect the vacuum and electrical connectors from the programmer. Remove the heater core cover mounting screws and pull the cover away from the heater housing. Remove the two core mounting screws and carefully lower the heater/air conditioning assembly from under the dash. Installation is the reverse of removal. For a 1999 Seville or 2000-2005 model, the heater core is also located in the passenger compartment, behind the instrument panel. Disconnect the heater hoses at the firewall and remove the instrument panel. Remove the heater core cover mounting screws and pull the cover away from the HVAC assembly. Remove the heater core retaining straps and mounting screws, then remove the heater core from the HVAC assembly. Installation is the reverse of removal. For 2006 and later models, the heater core is contained in the HVAC assembly, which includes the heater core, evaporator core, and various mode doors and actuators. Have the air conditioning discharged by a qualified technician. Remove the right engine mount strut, windshield washer fluid heater, engine trim cover, and upper tie bar in the engine compartment. Disconnect the evaporator hose and heater hoses from the core. Remove the brake pedal assembly and reposition the carpet to allow room to move the HVAC assembly. Remove the instrument panel center support bracket and reposition the auxiliary air duct. Remove the instrument panel carrier and disconnect the HVAC assembly electrical connectors. Remove the heater core-to-NC pipe cover screws and remove the heater core. Installation is the reverse of removal.
