What exactly does a warmness exchanger do within a package heat & AC element? If they heat exchanger go bad, what are the symptoms of this?

If they heat exchanger go bad, what are the symptoms of this?
How much is a 1969 snap on tool...
Answers:    Is this is a carton unit beside gas heat? The boil exchanger is the part that heat the air. The blower forces the room nouns around the exchanger which heats it. The gas burner heat the inside of the exchanger.

If it gets a crack or rusts out you will hold combustion byproducts entering the building.