There is no standalone "1998 Lincoln air conditioner"—the A/C is a vehicle system. Lincoln is Ford's luxury brand; 1998 models include the Town Car, Continental, Mark VIII, and Navigator.
If your 1998 Lincoln's A/C needs refrigerant (recharge), here's the general process:
Recommendation: A/C work requires EPA Section 608 certification and specialized equipment. Have a qualified automotive A/C technician diagnose and service the system. DIY recharge cans risk overcharging, contamination, and missing underlying faults.