Antifreeze Smell from Air Conditioning

I have a 1998 Ford Expedition. It runs perfectly, however, recently, I have been smelling antifreeze coming from the A/C ducts.

I live in Costa Rica where it is 90 degrees every day. I have had no overheating and no loss of radiator fluids (or no significant loss). There is no water on the ground under my car either.

What do you think is the problem? Perhaps a heater core with a leak?

Unfortunately, we do not have a dealer in the area that I can simply pull into and get it checked out. They can repair the heck out of a Hyundai down here, but they are baffled by a Ford.

Thanks for your help!

Steve