How much freon on 1998 peterbilt 379?

The 1998 Peterbilt 379 typically requires about 20 ounces (or 1.25 pounds) of R-134a refrigerant for its air conditioning system. However, it's always best to consult the vehicle's service manual or check with a qualified technician for the precise amount and specifications, as variations can occur based on the specific configuration or modifications of the truck.