Air handlers and furnaces aren't typically found together in Mobile. If you rely on a furnace, you most likely don't need to spend time thinking about an air handler.
Air handlers are often used with heat pumps and deliver airflow across your home. Some units also offer secondary heating and cooling components to support the heat pump.
A furnace heats in a different way by pushing warm air into your vents, which circulate it throughout your residence. As furnaces depend on combustion chambers to produce heated air, they don't use some of the pieces you'll see in a standard air handler.