it is probably a bad heater core
No you cannot sue unless it was sold with a warrenty.
The water is not circulating through the heater core or you have a control problem. If the heater is putting out heat then it is probably a control problem. If no heat then - water pump out, low on coolant, or maybe the therostat is stuck open.
Most likely your heater core is leaking.
Why the heater or defroster may not work in a 1993 Chevy Caprice Classic because of the heating core is going out.
Yes they have a heater/defroster.
heater core may be partly plugged .
The first thing that you need to do is check for a vacuum leak for the a/c and heater system, this is a very common.............
If you mean "why", then the answer is that there is a leak in the heater core.
The heater core is leaking coolant.
Your heater core is leaking in it's housing box and blowing moist air through the heater/defroster. Try bardall radiator stop leak. If no help, install new heater core. Chuck.