What type of freon is required in a 2001 Chevrolet silverado?

Answer 1

Source: wikipedia as a 'freon wiki' search in Google (0.08 seconds)

Freon is DuPont's trade name for its odorless, colorless, nonflammable, and noncorrosive chlorofluorocarbon and hydrochlorofluorocarbon refrigerants, which are used in air conditioning and refrigeration systems. Freon was initially developed in the early 20th century as an alternative to the toxic gases that were previously used as refrigerants, such as ammonia, chloromethane, and sulfur dioxide. Freon, in this case dichlorodifluoromethane, was invented by Thomas Midgley, Jr. with co-inventor Charles Kettering.[1] Each Freon product is designated by a number; for instance, Freon-11 is trichlorofluoromethane, while Freon-12 is dichlorodifluoromethane. In the 1990s, most uses of Freon were phased out due to the negative effects that chlorofluorocarbons and hydrochlorofluorocarbons have on the Earth's ozone layer.

Thus, Freon has not been used in auto A/C's since the mid 90's. The current refrigerant used is R-134a (NOT Freon, although people may casually and incorrectly refer to it as such).

In case you're curious, the DuPont trade name for R-134a is Suva.