This listing is for an original defrost duct for all 1966-67 Chevelle, Malibu & El Camino with & without factory air-conditioning. 

This is the piece that mounts to the top of the left hand side of the heater box.  It's function is to take air from the heater box and direct to both sides of the windshield through openings in the top of the dashboard. 

Very clean original condition.