Adding free on to 89 maxima
Your '89 Maxima uses an R-12 refrigerant, commonly known as Freon. R-12 has since been discontinued for environmental reasons...newer cars now use R-410a.
R-12 is very hard to obtain these days. You can find it on eBay, but you will need to be EPA certified to purchase. If you can obtain the R-12 somehow, make sure you get it in a kit that includes the hose, tap, and instructions as this will save you some headache.
If you cannot find R-12, I would recommend converting the A/C system over to the new R-410a. Most mechanic shops can do this for you for around $200-$300. The price they quote you should include a complete evacuation of the system, changing the required fittings, and recharging with R-410a, and maybe some PEG oil, depending on the compressor used.