Does it smell sweet?

Could actually be smoke, yes. But more than likely it is a heater core leak and it is steam not smoke.

 

And if by smoke, you mean the kind that smells like something is hot and/or burning... then you need to inspect the blower motor resistor and ensure that it is not damaged or coming into contact with some foreign debris (leaves, fuzz, etc.). It can be found in the passenger foot well, close to where the passengers left shin would be.