Where is the air conditioning low side service port on a 1998 ford expedition 5.4 liter engine?

The low-side service port on a 1998 Ford Expedition's A/C system is typically located on the dryer/accumulator. This is usually a cylindrical component near the front of the vehicle, often close to the condenser (the larger, usually black, radiator-like component in the front of the engine bay). It's commonly a smaller port, often with a blue cap.

However, the exact location can vary slightly depending on the specific model and any aftermarket modifications. It's best to consult a repair manual specific to your 1998 Ford Expedition 5.4L to be absolutely certain. A Chilton's or Haynes manual will show you a diagram of the A/C system with the ports clearly marked. You can also find diagrams online by searching for "1998 Ford Expedition A/C system diagram."

Caution: Working with refrigerant requires specialized tools and knowledge. Improper handling can lead to injury or damage to the A/C system. If you're not comfortable performing this task yourself, it's best to take your vehicle to a qualified mechanic or A/C specialist.