1971-1976 C3 Fresh Air Vent Control Knobs without Air Conditioning Restore factory original appearance and function to your C3 interior with our 1971-1976 Corvette Vent Control Knobs. These knobs are an exact reproduction of the original equipment GM used on Corvettes without factory A/C. Knobs are manufactured of black plastic and features correct grained design used on 1971-1976 models. Late 1969-1970 models featured smooth knobs without any grain pattern.