Freon, which is a type of refrigerant used in older automotive air conditioning systems (specifically, R-12 or chlorofluorocarbon CFC-12), is colorless and odorless. Therefore, you won't be able to see or smell it if it leaks from the air conditioner in a car. However, it's important to note that using R-12 is now restricted due to its harmful impact on the ozone layer, and most modern vehicles use R-134a (tetrafluoroethane) as the refrigerant.
R-134a is also a colorless and odorless gas, so detecting a refrigerant leak by sight or smell alone is not possible. Instead, mechanics use specialized tools, such as electronic leak detectors or ultraviolet (UV) dye, to identify and trace leaks in automotive air conditioning systems. The UV dye is added to the system, and when there's a leak, a UV light is used to make the dye glow, revealing the location of the leak for repair.