There are a lot of hidden parts inside of the dash that have to do with your heating and air conditioning systems, and they all have to be working perfectly to keep you comfortable.
Let’s start with where the air comes into the vehicle and enters the ductwork in the dash. That’s called the fresh air intake, and it’s usually located under the hood on the passenger side, right below the wiper. Many times that incoming air will go through a cabin air filter as it enters the ductwork. It’s important to keep that filter changed on a regular basis, to keep dust and other contaminants out of your interior.
As the air enters the ductwork inside of the dash, the blower motor pushes the air along. It has a “squirrel cage” fan blade on it, which is designed to move a lot of air. As the air continues through the dash, there are small doors inside of the ducts that open and close, directing the air where you want it to go. If you switch from vent to defrost, for example, different doors will open and / or shut, and direct the air inside of the ductwork to the appropriate area.
The doors inside of the ductwork are controlled by small electric motors that receive signals from your car’s computer to move in a certain direction to open or shut a door. Sometimes those small motors go bad, or one of the levers on the end of the doors can break as well. Either way, if the part that is broken is way up inside of your dash, you might have to pay a LOT of labor for the mechanic to get to the part. They might even have to pull part of the dash out of the vehicle to get to the part!
The main parts in the dash that either warm you up in the winter or cool you down in the summer are inside of the ductwork as well.
There is a heater core that has hot antifreeze flowing through it, and in the wintertime the doors inside of the dash direct the air through the heater core to get the air hot. Then it’s directed out through the ductwork to the interior of the car.
The other part is what’s called an evaporator core, and it has cold refrigerant running through it. In the summertime the air in the dash is directed through this very cold part, cooled way down, and then sent out into the passenger area of the vehicle to cool you down.
There is also a blend door inside of your dash that’s between the heater core and the evaporator core, and it can open or shut in either direction to regulate how much air is going through each of the parts. That way the air coming out of the dash and into your interior is not too hot or too cold. It should be juuussssst right!