Heater is not working. Blows air but absolutely no heat.

What is your question?

Ever since I bought the truck the heater hasn't worked. It makes no strange noises when running it just blows cold air. and the only setting that works is high. Truck is running at normal temp. antifreeze is full. Just recently when I turn it on it smells really strong like antifreeze. What's going on? How do I fix it? Thanks for the help guys.