The open vent you see is directed to the passenger right side dash vent. In your year car, the vent opening in the trunk was capped by the factory (the amber broken plastic is the vent cap). here is a picture of the vent cap. It's actually a bit more clear than amber. The amber color comes from age as it hardened and cracked. These caps are no longer available but you might find a suitable substitute if you feel you need to cap it. Left uncapped will do no harm
With the vent capped the A/C blower now directs air to that vent with a hose from the inner bulkhead inside the passenger footwell. (excuse the wiring mess) You can see the longer paper hose on the passenger side
