2002 Pontiac Grand Prix...I need to know where the intake is to add a/c coolant

Under the hood towards the front of the engine compartment is the condenser. This has two lines on it. One is larger than the other. The larger line is the low pressure line with a blue cap on the service port. To fill the freon you must get a can with a hose that hooks up to this fitting. While the a/c is on max, open the valve on the freon(134a) can and the compressor will start to run. When the line starts to sweat check the temp coming from the vents, the white sticker under the hood will tell you the a/c system capacity. Don't overfill it. Good luck