Replacing a Volkswagen Jetta's heater core is simpler than most other cars. Since the core is located underneath the driver side footwell, it is easier to access than those located behind the dashboard. Still, you must use caution, since you are dealing with liquids like engine coolant.
Unplug the Jetta's negative battery cable, making sure you have the radio's anti-theft codes to enter afterwards.
Take out the facing wall in the plenum chamber and place appropriate drip trays under the engine. Use hose clamps on the coolant hoses and disconnect the hoses from the heater core.
Drain the engine coolant carefully from the system. With a clean container under the core's lower connection, connect a piece of hose to the upper connection and blow coolant from the core into the container with a compressed air gun.
Disconnect the connection flange bolt linking the heater core connections so the coolant pipes can move.
Remove the trim and air vent from the driver side footwell, then remove the heater core trim. With strong foil and absorbent paper below the heater core, open the hose clamps and disconnect the coolant pipes, then remove the heater core.
Push the new heater core into the heating/ventilation unit.
Insert sealing rings coated with coolant into the connections on heater core. Connect the coolant pipes to the core, tighten the hose clamps (about 1.5 foot pounds on newer models) and reapply the bolt to the connection flange.
Reconnect all other hoses and replace the engine coolant in the system. Look for any leaks in the coolant circuit for leaks, especially between the coolant hoses and heater core.
Connect the negative battery cable, then evacuate, charge and leak test the air conditioner. Let the Jetta's engine run to normal operating temperatures, then observe the climate control operation and double-check for leaks.
