Where is the low pressure side of ac in a 1998 Ford Explorer?

On a 1998 Ford Explorer's A/C system, the low-pressure side is typically found at the smaller diameter of the two AC lines. You'll find this line connected to the AC compressor (usually on the engine's front) and going towards the evaporator inside the vehicle's passenger compartment. There's usually a service port (with a Schrader valve) on this line for adding refrigerant. This port is often capped. Look for a smaller diameter line near the compressor with a cap that looks like a tire valve stem – that's your best bet for identifying it visually.