The low-pressure AC valve (also called the low-side service port) on a 1998 Pontiac Grand Am is typically located on the
dryer/accumulator. The dryer/accumulator is part of the AC system and is usually found near the front of the vehicle, often on the passenger side of the engine compartment, but its exact location can vary slightly. It's a cylindrical component, sometimes with a sight glass. Look for a smaller fitting with a cap on it; this is your low-pressure port. It will be next to a similar fitting for the high-pressure side. The low-pressure fitting is usually smaller in diameter.
However, without visually inspecting the vehicle, this is just a general location. A repair manual specific to a 1998 Pontiac Grand Am will provide the most accurate and detailed information on the location of the low-pressure AC valve. Using a diagram from a repair manual is highly recommended to avoid mistakes.
