Most people have central air conditioning, especially if they live in a warm climate. The common misconception is that you have to employ a contractor to do this for you. While you might want to hire an electrician to make sure your mains are hooked up correctly, this is definitely a do-it-yourself kind of project. The only other thing to be mindful of, like most home improvement projects, is to check with the building codes to make sure you're in compliance.
Plan and install the ducts. Use the floor plans for your home to map out where you will place the ducts. The goal is to make sure you have enough space in easily accessible areas.
Put in the air handler near a condensation drain. Pay attention to the manufacturer's guidelines here, but in general, air handlers are installed in the basement. The handler should be able to run outside the home and away from foundations.
Install the compressor. If you are going to hire an electrician, this is where you may need their help. Again, it is important to follow the manufacturer's instructions, but in general, compressors should be placed 10 to 12 inches from your building. Make sure you turn off the mains to your home before you get started. The compressor should be placed on top of a plastic, leveled flat.
Drill holes through the outer wall. One will be for the refrigeration tube and the other for the electrical tube. These holes should then be filled with a strong filler to guard against leakage. Be sure to connect the compressor to the mains before you switch them back on.
Check with an electrician. After you connect to the mains, it is important to make sure it is capable of carrying the load. Having an electrician check the requirements and the capabilities will ensure proper installment and safety.