The Plenum Chamber

This is a Plenum Chamber, essentially an air handler for the HVAC system. A series of vacuum operated motors open and close doors within according to what setting is requested, (i.e. a/c comes out the vents, defrost comes out at the windshield, heat comes out the floor, etc.).

The Plenum Chamber is connected to the heater case. And where is the heater case located?

The heater case sits behind the instrument panel !

Removing the radio and HVAC controls in the center of the instrument panel allows you to see the Plenum Chamber. But just because you can see it doesn't necessarily mean you can actually get to it.

The Plenum Chamber connects the heater case output to the dash and windshield vents. But it is attached to the instrument panel. This means the instrument panel must be moved in order to access it.

After disconnecting several wiring connectors and removing a bunch of fasteners, the instrument panel can be shifted out of the way. The passenger side is pretty straight forward.

The modern instrument panel design routes all the wiring within to a few large connectors. This is much more convenient than having to disconnect each individual component.

After disconnecting several of the large electrical connectors, unbolting the steering wheel shaft, and removing a few more fasteners, the driver's side can now be slid rearward.

This is where heated or cooled air from the blower motor gets distributed. When heat is requested, air is directed out at the floor vents shown above. When a/c or defrost is requested, air is directed out through the large rectangular opening and into the Plenum Chamber.

The Plenum Chamber is bolted to the instrument panel. Several small fasteners must be removed.

Two vacuum connectors must be disconnected as well.

Removing the Plenum Chamber is a not-as-simple-as-it-seems process of twisting and turning.

Twisting, turning, holding your tongue at the right angle, etc. allows the Plenum Chamber to be removed from the instrument panel.

And voilà !

So why did I have to do all of this ?

This is the connection from the vacuum motor (R) to the vent door. When a/c is requested, this vacuum motor opens the door to direct air out through the dash vents. This is done via the vacuum motor drawing the silver metal rod inward, thus moving the door on a pivot point.

When the small black plastic tab on the vent door breaks, the door doesn't move. The angle at which the Plenum Chamber is mounted means the door will be closed, and all airflow will be directed out the floor.