Q: How to remove and install a heater core in a Lincoln Navigator?
A: Take the vehicle to an air conditioning shop to discharge the AC system. Disconnect the negative battery terminal and drain the cooling system. Remove the instrument panel, and disconnect and plug the heater hoses and Evaporator lines at the firewall. Remove the plenum demister tube, the bracket on top of the heater core housing, and the heater core cover. Carefully remove the heater core. When reinstalling, ensure the foam sealing material is intact. Reverse the removal steps for the rest of the installation. Install new retainers and O-rings on the heater core hoses, refill the cooling system, and check for coolant leaks. Have the AC system charged. Navigator/Expedition models have an optional rear heal/AC system, with removal and installation similar to the front system.