RepairPal Certified shops can diagnose and repair your 1999 Buick Century. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
If you need to top it up you have a leak, you need a tech to look at it.
It's more then likely 134 refrigerant if you do try to do it you self which I recommend not to.
Buy the refrigerant with dye so you can see we're the
Leak is