Air handlers and furnaces aren't often used in the same home in San Antonio. If you have a furnace, you most likely won’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 sending warm air into your vents, which send it throughout your residence. 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.