However, I strongly advise against attempting to add refrigerant yourself. Adding refrigerant requires specialized equipment and knowledge to ensure proper pressure and avoid damaging the system. Improperly adding refrigerant can lead to further complications and costly repairs.
Instead of attempting a DIY repair, take your 2000 Ford Expedition to a qualified mechanic or auto AC specialist. They have the necessary tools and expertise to diagnose the problem, identify the cause of the refrigerant leak (if there is one), and properly recharge the system.