See the "Bentley" at http://www.rb.com/catalog/VV91.htm

It is published for North American use, and many pages will
contain data not applicable to European Transporters,
especially those pages describing electrical components.

"Heater core" is a water radiator used for heating the
interior of the Vanagon.  Those water cooled Vanagons from
1983-on generally have two, and engine coolant is circulated
through them unless some part of the system breaks, causing
a water leak.  Your air cooled Vanagon has none, relying
rather on the engine's air cooling system to duct heated air
to the interior, sometimes optionally supplemented by a
gasoline-fired heater.