If the vehicle is equipped with air conditioning, have the air conditioning system discharged at a dealer service department or service station. Turn the heater control setting to HOT and drain the cooling system. Disconnect the cable from the negative terminal of the battery, then loosen the hose clamps and disconnect the heater hoses from the heater core tubes at the firewall. Remove the rubber grommets where the heater core tubes go through the firewall, disconnect the air conditioning refrigerant lines and rubber grommet from the evaporator core if the vehicle is so equipped, unbolt the steering column and lower it, then remove the entire instrument panel, unbolt the fuse panel and any remaining components attached to the instrument panel reinforcement bar, remove the floor heater ducting and any remaining electrical connectors, remove the defroster ducts from above the heating/cooling unit, remove the evaporator core housing assembly or passenger side heater duct on models without air conditioning, remove the bolts/nuts securing the heater unit to the firewall, disconnect the control cables from the unit, pull down and back on the heater unit, remove the heater core from the heater unit, reassemble the heater unit and check the operation of the control flaps, reinstall the remaining parts in the reverse order of removal, re fill the cooling system, reconnect the battery and run the engine, check for leaks and proper operation of the system, and have the air conditioning system recharged if equipped.