A Lincoln Navigator's heater core is located behind the right front quarter trim panel. You will have to open up the panel from the vehicle's interior if you need to replace the core. You also need to drain the cooling system before anything else.
Drain and recover the refrigerant from the cooling system. The system must be cool and the engine off to avoid injury.
Remove the quarter trim panel on the right hand side. Detach the upper air duct on the auxiliary housing and remove the auxiliary line bracket.
Clamp off and then disconnect the heater hoses. Disconnect the drain hose, blower motor and the electrical connectors for the blower motor resistor electrical actuator.
Remove the auxiliary climate control housing and the access cover to the evaporator/heater core. You can now remove the heater core.
Install the replacement heater core into the Navigator and replace the access cover and climate control housing. Reconnect all hoses and electrical connectors, using new O-ring seals where they are needed.
Clean and lubricate the coolant hoses if necessary, using plain water. Lubricate the refrigerant system with clean PAG oil.
Connect the auxiliary line bracket and the upper air duct. Reconnect the quarter trim panel.
Refill the engine coolant level. Test the refrigerant system for leaks with a refrigerant leak detector. Evacuate the system of air and charge it with an R-134a Service Center.
