How to Fix the Heater in a Ford Expedition

Disconnect the Expedition's power supply before working on the heating system by unplugging the negative battery cable. Drain the cooling system, removing the drain plug at the radiator and then the engine block, letting the coolant pour into a clean container.

Inspect all pipes and lines in the heating system and replace any that are cracked, brittle or leaking. The lines are connected with quick connect fittings, so press on the taps to release them. Use new seals or O-rings when connecting the new hoses.

Replace the thermostat if it is stuck in either the open or closed position. To remove it, remove all hoses from the thermostat housing with a ratchet wrench or pliers, disconnect the upper mounting bracket for the power steering reservoir and remove the mounting bolts for the thermostat housing with the ratchet.

Replace the coolant if it is old or contaminated.

Clean out leaves, bugs and other debris from the condenser. This can be done with a fin comb or compressed air.

Flush out the heater core if one of the heater hoses is cool. Disconnect the hoses at the firewall and run water from a garden hose into the core through the opening. If there is still no heat circulation after you reconnect the hoses, disconnect the hoses completely and flush them.

Have the air conditioning system discharged. Because you are dealing with refrigerant contained at a very high pressure, this must be done by a professional at a dealer service shop or air conditioning shop.

Remove the instrument panel (dashboard) from the vehicle. With the steering wheel in the "Lock" position, pry off all scuff plates, kick panels, trim panels and center console. Disconnect all ground cables and electrical connectors. Remove the passenger airbag and pry out the defroster grilles, then remove all screws mounting the panel and lift the panel out with an assistant's help.

Disconnect the heater hoses and the evaporator lines at the firewall by squeezing the connectors' plastic tabs, then plug the open lines with rubber. Disconnect the main vacuum line and remove the demister tube, which looks like a vacuum tube with a square, bristled end.

Unscrew the screws holding the bracket above the heater core housing and remove the bracket. Take off the heater core cover by removing its screws, then pull the core out, making sure you don't tear the foam material surrounding it.

Install the new heater core into the housing, making sure the foam material is intact. Place the cover and bracket back on the core and reapply the mounting screws.

Reconnect all the lines to the firewall, using new retainers and O-rings on the connectors. Reinstall the entire instrument panel, refill the coolant, connect the battery system and have the air conditioner recharged.