i have a 93 chev. corsica. when i turn on heater or defroster, it does not get hot. fan works, just don't get hot. air conditioner does not work also. more concern about heat.

have a coolant flush done it the doesn't help then the heater core is bad with the a/c it maybe the high pressure switch on the a/c system or low freon

OR the conrtols in the dash may be screwed up. They ae vacuum controlled so if you have any broken vacuum lines under the hood that might be the problem. There are a bunch of lines by the battery, you might want to start with those.