I have a "96" Buick p. a. ....the heater motor won't work but all the lights come on .....it won't get warm at all....cold air comes out....
did you fill up the coolant to the "full cold" mark on the reservoir bottle...anyways sounds like a stuck open thermostat~ change that one~ https://www.google.com/#q=1996+Buick+Park+Avenue+thermostat
if you've "panic" filled with water at some point, please get the cooling system flushed and new coolant and thermostat put in....good day sir~