FrançaisEnglishThe ins and outs of the systems that keep you comfy in your car
It’s magic in your dashboard. The system that pumps out hot air when you want it and cold air when you need it. It can even take the frost and fog off of the inside of your windshield. But how does climate control work in your car? There are a few surprisingly simple systems that work together to keep you comfortable as you drive, and this is how they work.
Let’s start with the climate control system, the panel where you tell your vehicle what to do. These have options that range from the basic fan speed, hot/cold, and where the air blows to precise temperature controls that let four passengers set four different temperatures.
Older vehicles use cables to control the systems that change the air temperature and where the air blows, modern ones use wires and electric motors. But both do the same thing inside your dashboard.
When you want warm air, turning the knob sends air over the heater core. This is a small radiator that lives in your dash. Hot coolant flows from the engine and through the heater core and that warms up the air that passes over it, which then blows over you. The heater core needs hot coolant to work, which is why your vehicle doesn’t give you heat in the winter until the engine warms up.
When you don’t want hot air, a door blocks airflow over the core. If that door stick or the motor fails, you’ll notice you get heat when you don’t want it or cold air when you want hot.
The blower motor lives behind the glovebox and pulls fresh air from outside then blows it through the cabin air filter (if you have one) then through HVAC (heating, ventilation, air conditioning) system onto you.
If there’s no air flowing when you turn on the fan, that’s the blower motor or the resistor that gives the motor its multiple speeds. Some cars have two or more blowers for dual climate control systems, so if you have air on one side and not the other, that’s a good place to look.
The air conditioning, or AC, system is the most complex part of the entire HVAC system, with the most mechanical parts.
It starts at the engine with the air conditioning compressor. This part compresses the refrigerant in the AC system, raising its pressure. The high-pressure refrigerant then passes through the condenser, which is a heat exchanger that is normally mounted in front of the radiator. Inside the condenser, the AC refrigerant turns from a gas into a liquid by shedding heat to the air flowing through it.
From there the refrigerant passes into the evaporator, which is mounted inside your vehicle along with the heater core. In the evaporator, the refrigerant boils and that sucks the heat out of the air passing through it. With all of its heat pulled out, the air is then cold and dry. Then the air gets blown through the vents and cools you off.
There are some other parts in the system, like the dryer (which dries the refrigerant) and the orifice valve which marks the point in the system between high and low pressure, as well as sensors and relays. But those three components are the most important.
Along with the refrigerant itself, that is. The most common refrigerants are R-12 (pre 1997 or so), R-134a, and R-1234yf (since around 2018).
Losing refrigerant is the most common reason an AC system will fail, but you need to do more than just recharge the system to fix it. The AC system should always be airtight, a leak is a failure point that will repeat itself. You can get kits that let you recharge your AC at home, but make sure to fix the leak first.
To help find and fix the leak, you can get a dye kit. Using UV dye and a special light, these kits highlight where the system is leaking so you can repair or replace the component.
Closed AC systems are hazardous to work on and releasing refrigerant can cause severe frostbite. So, AC system service and filling is best left to your NAPA AUTOPRO service specialist.
Last but not least is the air box. This is what holds the heater core and evaporator and directs the air to the dash, glass, or foot air vents. It’s really a big plastic box with ducts, hoses, and doors, with those ducts and doors controlled by a cable or electric motor and gears. These don’t fail often, but an electric motor or gear can fail.
In most cases, a gear or motor can be replaced without removing the air box. But some can’t be, and that means removing the entire dashboard of your vehicle. So, if you suspect part of the air box (aka heater box) has failed, it’s worth a look from your NAPA AUTOPRO specialist to be sure before you take apart half of your vehicle.
Author: Philippe-Mathieu 
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