Do-it-Yourself Central Air Conditioning

Choose a unit that works for your building, after assessing it thoroughly. You should base your decision on your home's square footage, insulating capacity and orientation. Units vary in their cooling capacity as well as their efficiency rating. A contractor can help you make an educated decision.

Make sure the proper duct work is installed throughout the home. Duct work is often present in conjunction with an existing furnace or heater. Older homes occasionally require a ductless system if ducting is too difficult to install.

Locate your furnace's supply plenum. This is a compartment within your furnace where your evaporator coil will be placed. If necessary, construct a sheet metal shelving unit on which the coil will sit. Set the evaporator coil in the plenum with the supply lines facing out. The evaporator coil works by taking cooled air and distributing it throughout the home through the ducting.

Find a good spot to place your condensing unit. This is the large, outside unit where hot air from the inside is condensed and released outdoors. It needs a spot with plenty of air circulation, ideally out of hearing and eye range.

Place the condenser on the condenser pad. Cut a small hole on the exterior wall near the unit, using a saw. This is where your supply lines will run and it should have an easy passage to the evaporator coil.

Connect the suction line to the surface valve on the condenser. Run this line through the hole and to the furnace, but do not connect it to the evaporator coil yet.

Connect the liquid line to the condenser and run it along the same path as the suction line.

Set up low-voltage lines between your compressor and evaporator units and the main power supply.

Install a thermostat and connect it to the furnace and the main power supply.

Contact a contractor for the remaining steps. The contractor will discharge the refrigerant, hook up the high-voltage power, solder the supply lines, check your work and complete any remaining details.