GM had varying definitions, depending on the year of vehicle. In 1966 it meant the Comfortron A/C system, the one with a dial for temp control.
C.A.C. = "Controlled Air Comfort" manual control, fresh air ventilation.
Cars of this era were either manufactured with:
- A/C (the only factory air-conditioning system available)
- C.A.C. (manual control, fresh air ventilation only)
- C.A.C. A/C (C.A.C. & optional factory air-conditioning)
- Comfortron A/C (optional factory auto temp./climate control air-conditioning)
- CoolPack A/C (optional under dash air-conditioning unit, usually dealer installed)