GM 22784517 Core Assembly, Heater

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.

The heater core works inside the heater and evaporator unit, passing engine coolant from your engine while you drive. The heater core works by using fins to spread heat from the coolant to air flowing alongside it. It has two specific tube connections, and the correct placement of the heater hoses is essential before any work can be done. To safely replace the heater core in these two models, start by disconnecting the negative battery cable, using caution to drain the coolant fully. Ventilate well to prevent burns from steam, and collect all used coolant in a sealed container to keep pets safe. First, pull out the heater core hoses, then unclip the right corner cover and remove the glove box frame. After that, remove the programmer screen if your car has it and detach both the electric and vacuum wiring. After keeping connections to the installer, you can take off the heater core cover. Pull out the heater core's mounting screws and remove the core completely. Start by attaching the new heater core with retaining screws, putting the heater cover back, then linking and connecting the vacuum and electrical connectors and air mix valve link for the programmer. Once done, put on the heater core hoses. Before being done, attach the negative battery cable, put coolant in the system, and make sure the air mix valve works correctly by turning the temperature to 90°, waiting for the programmer arm to reach the highest heat, confirming the valve moves easily, starting with maximum heat before using a torque wrench to tighten the valve to closed. Reassemble everything by putting back the right side sound insulator and glove box module in place.

If the blower motor does not operate, check the blower motor fuse and replace it if necessary, inspect the wiring for loose, damaged, or corroded contacts and repair as needed, examine the blower motor switch and resistor pack for open circuits, and repair or replace them if required. For a heater that blows cool air, verify the engine coolant level, topping off and bleeding the air from the cooling system if low, and check for leaks. Ensure the engine coolant operating temperature is within specification, and if it is below, investigate a potentially damaged or stuck thermostat. Assess the heater control valve operation, ensuring the cable or vacuum hose is properly installed, and test the valve by moving the heater temperature control from hot to cold. With the engine at normal operating temperature and the control in the full hot position, feel the heater hoses; if one is hot and the other is much cooler, replace the control valve. If the heater steams the windshield when used, check for a loose cooling system hose clamp or leaking coolant hose near the engine firewall or under the dash, and repair as necessary. Look for a sweet odor and fluid dripping from the heater floor vents, which may indicate a failed or damaged heater core. Pressure test the cooling system with the heater set to the fully warm position and check for fluid leakage from the floor vents; if leakage is confirmed, remove and replace the heater core assembly, noting that on some vehicles, disassembly and removal of the dashboard may be required to access the heater core.

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.