A heater core acts much like a radiator, in order to heat the inside of a vehicle. Prior to replacing a heater core, it is a good idea to verify that heating problems cannot be attributed to a leaky hose or an improperly connected clamp. If those components are intact, then move forward with replacing the heater core. Although the heater core itself is not difficult to replace, getting to the assembly on your Audi A6 Quattro can be a challenge since it is located under the dashboard on the inside of the vehicle.
Move the front seats as far backward as possible to allow for enough space to work.
Disconnect the negative and positive battery cables by loosening the clamps, and remove the battery.
Remove the cap on the coolant recovery tank to relieve the pressure from the system. Drain the coolant from the system by disconnecting the heater hoses from the tubes in the engine compartment, and applying compressed air to the upper tube. Catch the coolant as it comes out of the bottom tube. Remove the tube-to-chassis grommet on the heater core.
Remove the heater core storage compartment on the driver's side of the vehicle by loosening the bolts with a socket wrench, and the brackets from the heater core tubes from the passenger side of the vehicle.
Pull the heater core from the A/C-heater housing by tugging slightly. Pull the two coolant lines out of the heater core and remove the old heater core entirely.
Replace the old heater core with a new core, installing new clamps and O-rings at all connections. Insert the coolant lines back into the heater core during installation.
Replace the bolts and brackets from the heater core tubes on the passenger side of the vehicle. Replace the heater core storage compartment on the driver's side of the vehicle, and replace all bolts previously removed.
Reconnect the heater hoses at the heater core, tubes-to-chassis grommet, cap the to coolant recovery system and battery. Reconnect the positive and negative battery cables to the battery. Test the new system to ensure there are no leaks in the cooling system. Add coolant as needed to bring the level up to the proper amount.
