Walk through the pits of a vintage drag race or cruise the main drag of a car show, and you'll likely hear a handful of "old timers" belly-aching about the good ol' days before billet aluminum and fiberglass snuck their way into the heart of hot rodding. One thing you won't hear any complaining about, however, is the plethora of highly adaptable and efficient air conditioning units now available on the aftermarket for rods of just about every year, make, and model. While A/C was once considered a luxury item reserved for only the most well-equipped luxury cars, climate control is now standard on virtually every new vehicle on the showroom floor. Furthermore, many of the same folks who tell tales of trekking through the snow barefoot on the way to school would never even consider making a midday rod run without their A/C blasting. Air conditioning has become a way of life for many of us, and new technology makes these systems lighter, more efficient, and more environmentally friendly than ever before. In this article we'll start with the basics-how air conditioning works-then move on to some tips for setting up a new system, as well as making your existing system work better. With a little planning, forethought, and a few days' worth of work, your interior should be as cold as Martha Stewart's heart.
Physics 101A common misnomer about air conditioning is that the system somehow magically creates cold air, which it then blows out the vents into your car. The truth of the matter is that air conditioning is all about heat. If that sounds confusing, read on. A properly functioning A/C system is basically a giant circuit designed for transferring heat. Essentially, heat is pulled from the air inside your car, carried into the engine compartment via hoses running through the firewall, and transferred into the fresh air flowing through your grille. All of this happens thanks to a few basic rules of physics, namely heat transfer, evaporation, condensation, and pressure.
The basic rule of heat transfer is that "cold" doesn't actually exist; cold is the absence of heat. The only time something seems cool is when its heat has been removed and transferred somewhere else. Furthermore, heat is constantly trying to travel from warmer to colder areas in an attempt to create balance, and the greater the temperature difference, the faster it moves. An example of this occurs when you look across a highway in the middle of a summer afternoon. The ripples you see coming off the ground are actually heat waves; the asphalt is transferring its heat into the cooler air surrounding it. As the asphalt cools down, the air is heating up. Another example occurs when you put a hot cup of joe on the counter, only to come back an hour later to a cold cup of coffee. The coffee doesn't magically change temperature; the heat of the liquid was transferred/absorbed into the cooler atmosphere of the room. This type of temperature change will always occur when the ambient air temperature is different from the object in question; heat is constantly trying to stay consistently dispersed.
The second principal necessary for air conditioning is called Latent Heat of Evaporation. Without getting too complicated, this rule basically states that it takes a lot of energy to turn a liquid into a gas. In most cases that energy comes in the form of heat, and if a liquid absorbs enough heat, it will evaporate into a gas, taking the heat with it as it goes. For example, anyone who has spent time in the hot sun knows that the best way to stay cool is to dump a bottle of water over your head. Even if the water is room temperature, rather than ice cold, you'll still cool off. Here's why: In order for the water to evaporate off your body, it absorbs tremendous amounts of heat/energy as it transforms into a gas. This process essentially transfers the heat from your skin to the surrounding atmosphere, cooling you off in the process. Your skin didn't get cooler, you just removed some of the heat.