Q: How to remove and install a heater core in a Lincoln MKX?
A: This is a difficult procedure for the home mechanic, involving numerous hard-to-find fasteners, clips, and electrical connectors. Have the air conditioning system recovered by a dealer service department or by an automotive air conditioning shop before proceeding. Disconnect the cable from the negative battery terminal. Drain the cooling system. Disconnect the heater hoses from the heater core inlet and outlet pipes at the firewall, then disconnect the thermostatic expansion valve and the two refrigerant pipes. Remove the instrument panel. On V6 models, remove the lower cowl grille panel to access some HVAC unit fasteners. Tag and disconnect the cables and electrical connectors from the HVAC unit. Remove the housing-to-firewall nuts. The heater core is in the center of the HVAC unit, to the left of the blower motor housing. Remove the heater core cover screws and pull the heater core out of the housing. Installation is the reverse of removal. Reconnect the heater core inlet and outlet hoses at the firewall. Use a new gasket where the two air conditioning pipes meet the expansion valve at the firewall. Refill and bleed the cooling system. Have the system evacuated, recharged, and leak-tested by the shop that discharged it.