The heater unit is located in the center of the vehicle, along the firewall. The heater system is a bi-level system, designed to direct air through the vents to either the windshield or the floor and cool air to the panel vents. On Sonata this system also includes ducts that direct air to the rear seat passengers.
The air conditioning system is designed to be activated in combination with a separate air conditioning switch installed in the control assembly and the fan speed switch. Some Sonata models are equipped with an electronically controlled system.
The control assemblies used vary depending on year and model. Some models use cable operated control heads, that route cables from the control head to the various air doors in the heater/air conditioning case. Other models use a vacuum control system to operate the various air doors.