What is a Heater Core Box? Where is it located? 
How does a heater box work? The Heater Core is in some ways similar to the Radiator, the Heater is used to warm the inside of your Vehicle, taking the heat from the coolant. While the Radiator cools the coolant in the Motor. As your Engine starts warming up, the Coolant absorbs the heat with the aide of the Water Pump it passes through the main Radiator cools below boiling point. 
The whole system is kept at a constant temperature by the Thermostat. So, when our customer turned on his heater all that blew threw was cold air, instead of the warm air which was created by a valve that opened so your hot coolant can flow to the Heater Core then comes thru the car with the coolant close to 200 degrees, which is great for keeping feet warm and clearing a foggy windshield. Some vehicles have dual controls (which is truly awesome), where the driver and front seat passenger can each enjoy the temperature to their need real hot or a cool 70 degrees. 