Can I use the new A/C refrigerants in my 91 LeBaron?

Ask at the parts store. The computer should list the type of refrigerant(I believe R-12). Otherwise, check your owners manual to see what kind was used and call the parts store and see if they carry it.If it used R-12 refrigerant, which is expensive, but still available. There is a conversion that can be done to accomodate R-134a refrigerant but, you have to consult shops for this. You cannot just add R-134a to your current system.