How do you add freon to 1990 Pontiac Transport?

To add Freon to a 1990 Pontiac Transport, first locate the low-pressure service port on the AC system, typically found on the larger diameter aluminum line. Ensure the AC is running and the thermostat is set to the coldest setting. Attach the refrigerant can to the port and follow the instructions on the can to add Freon, making sure to periodically check the pressure gauge. Always wear safety glasses and gloves, and avoid overcharging the system.