The Individual Parts
If you're buying a complete aftermarket A/C kit for a specific car, there aren't very many options available when it comes to the crucial parts-but not everyone has a popular car with an available kit. In that case there will be some improvising involved. Thankfully, the major A/C companies can walk you through it, but we're going to explain some details on the individual components if you feel like piecing it together yourself.

The Compressor
A compressor is just a pump, but the essential point to consider is the capacity of the compressor relative to the rest of the A/C system. Contrary to popular belief, bigger is not necessarily better, and in many cases too large a compressor can actually result in decreased cooling and component life due to excessive pressure. In most cars, a compressor with 8-9 ci of displacement is enough to cool sufficiently. In almost all cases in the aftermarket this will be a Sanden unit, usually the SD-508 rated at 8.4 cfm, unless you specify that you'd like to use something else (such as a vintage York/Tecumsah or Frigidaire compressor or a late-model unit such as a Nippondenso or Harrison). Any system can be adapted to work with these compressors, but efficiency could suffer depending upon the application. Ask the tech guys at your A/C company of choice for specific recommendations.

No matter which compressor you choose, you'll be mounting it to the front side of the engine in some way. If you're beginning with a car that had factory A/C or an A/C option, the factory brackets and pulleys can often be used with little to no modification (depending upon the compressor). Otherwise, multiple mounting options are available from the various A/C companies as well as pulley specialists like March Performance and Billet Specialties. Whatever bracket system you choose, just make sure the belt makes at least one-third of a wrap on the compressor pulley, and that there is a way to maintain proper tension on the belt in the form of a tensioning link or an idler pulley. Also remember that you'll need a crank pulley with a groove that lines up with the compressor if the engine isn't equipped with one, so if you're pondering upgrading to a serpentine belt or more aesthetic brackets, this is the time to do it.

Aftermarket bracket kits such as this one from March Performance can add style to the front of an engine and allow custom mounting locations to accommodate for engine swaps. Remember, if the compressor mount deviates from the stock location, make sure allowances are made on the length of the A/C hoses.

The CondenserEvery company we spoke with said that the condenser is probably the most important element of the system since its performance will determine how well the A/C system can cool. Ideally you want to use the largest and most efficient condenser that can be packaged into the car. For cars with bolt-in kits, this will already be scienced out. However, with custom applications and street rods the amount of space available will vary, so careful measuring will be necessary to determine what fits.

Packaging is generally not a problem in most '50s, '60s, and '70s cars, which have ample room between the grille and the radiator support where airflow is best. Space can be at a premium on many pre-'50s rods, but a highly efficient condenser can help make up the difference. Vintage Air's general rule of thumb is to plan on a minimum of 264 square inches on a standard old-style two-row 51/416-inch copper tube-and-fin-type condenser, or at least plan on a newer, more efficient condenser such as the parallel flow design used in most new vehicles. Hot Rod Air prefers a greater surface area with at least 330 square inches of condenser surface for efficient cooling.

More important than size, airflow is the key to how efficiently a condenser can operate. Even the biggest, best condenser can only do so much without good placement in an airstream. Refrigerant is much more sensitive to temperature than water, so to receive the coolest air possible the condenser is always placed in front of the radiator rather than behind it, and there should be a gap of at least 31/416 inch to prevent heat transfer from the radiator. None of the companies we spoke with recommend remote-mount condensers (such as those mounted under the car) if there are other mounting options, since the warm and sluggish airflow under most cars will be insufficient without at least a separate electric cooling fan, but most of the companies do have kits available nonetheless.