go to an auto parts store and buy a recharge kit, and follow the instructions
It was a bad answered that talked about changing the antifreeze -- not the airconditioning freon.
THERE IS NO FREON IN A 98 IT IS R134
R134a
R134a
This is what I did for my Chevy prism 2000, it works fine: http://www.id-usa.com/how_to_recharging.asp
R134a
R134a
R134A
R134a
R-134
You shouldn't have to change freon, it doesnt go bad.
R134a