Which aspect is the correct description of the heater core in the HVAC system?

The heater core is indeed the source of heat in the HVAC system. It functions as a small radiator that allows hot coolant from the engine to pass through it, which then warms the air that is blown into the passenger compartment. When the driver or passenger selects the heat setting in the vehicle, the HVAC system directs air over the heater core, allowing the heat from the coolant to warm the air before it enters the cabin. This process is essential for maintaining comfort during cold weather, making the heater core a critical component for providing adequate heating within the vehicle.

In contrast, the other options describe different functions or components of the HVAC system that do not relate directly to the heating process. For instance, air discharge location control pertains to the directional flow of air but does not involve the heater core, while temperature regulation in air conditioning involves different components like the evaporator. The defrosting feature also works through the use of airflow and temperature controls rather than the heater core's function alone. Thus, identifying the heater core as the heat source accurately reflects its primary role within the HVAC system.