93 Dakota No heat

I have a 93 Dakota that does nothing but blow cold air. Any suggestions?

Radiator is full, heater hoses are hot, upper radiator hose is hot and under pressure, temp gauge is in the normal range. I tried blocking radiator with cardboard but that only made engine run hot with no change in heater output, so I pulled it back out.

Try the search in this forum. Lots of people have had this question, almost every day infact. Most likely, the heater core needs to be replaced.