2011 Dodge Caliber Heat -- Smelling Antifreeze every few days; no apparent leak

Hi, I have a 2001 Dodge Caliber Heat with approximately 100,000 miles; just purchased a few months ago.  The owner maintained it very well, and has a background with car engines, etc., so it is in excellent condition.  After driving it for several months, I am now smelling a definite antifreeze smell, especially when I turn on the fan -- sometimes with heat, sometimes with AC.  The previous owner examined the antifreeze reservoir and it is not down.  We see no other signs of a leak, including the temperature gauge seems normal.  I do no smell the antifreeze smell every day; but every few days, I smell it.  I'm afraid there is a small leak somewhere, as the smell is pretty strong when I smell it.  Does anyone have any ideas, suggestions?  Thanks.