Air handlers and furnaces aren't often used side by side in San Antonio. If you have a furnace, you probably shouldn’t need to think about an air handler.
Air handlers are typically paired with heat pumps and manage airflow throughout your home. Some models also have secondary heating and cooling parts to help the heat pump.
A furnace works in a different way by pushing heated air into your vents, which send it throughout your house. Since furnaces use combustion chambers to create hot air, they don't use some of the components you'll spot in a regular air handler.