Here are the pieces that make up the air duct distribution system under the dash. This is for a 67. 68 and 69 are slightly different in some areas. The Air Conditioning section of the 1973 Illustrated Parts Index has a good diagram showing all the parts and differences from year to year.
....Defroster End Duct -- Defroster Distributor -- Heater Case
Left Dash Outlet -- Lower Center Outlet -- Main Duct -- Right Dash Outlet
.................Left Hand Outlet Duct -- Center Dash Distribution Duct
....................Center Dash Outlet with chromed deflector
The second picture shows the Lower Center Outlet attached to the bottom of the Defroster Distributor. The Lower Center Outlet pushes into a clip at the back of the Defroster Distributor (at the bottom in the picture) and is held at the front with 2 screws. The Illustrated Parts Index shows a different part number for the Defroster Distributor for each year, with 69s having a vacuum actuator.
Picture 3 shows the Defroster Distributor and Lower Center Outlet attached to the left side of the Heater Case.
Picture 4 - The Y-shaped Defroster Duct is mounted to the inside firewall. When the Heater Case and Defroster Distributor are in place in the car, the louvered opening on the top of the Defroster Distributor lines up with the bottom of the Defroster Duct. The gap is exaggerated in the picture. The Camaro heater seal kits come with a foam gasket to seal the Defroster Duct to the Distributor, and 2 seals that go between the defroster outlets and the underside of the dash. The Firebird parts manuals don't show these seals.
Picture 5 - The Defroster End Duct is attached to the left side of the Defroster Distributor. The outlet of this duct points down toward the driver's footwell. The Illustrated Parts Index shows the Defroster End Duct as a 67 only part.
Ducting Parts
Defroster Distributor and Lower Center Outlet
Defroster Distributor and Lower Center Outlet attached to the Heater Case
