Instructions for Installing Central Air Conditioners

Estimate the size of air conditioner you require in the home. Roughly 12,000 British thermal units can cool 1,000 square feet if your insulation is working properly. Alternatively, have a professional perform a residential-load evaluation of your home. This determines what size of air conditioner you need to install to achieve adequate cooling. Failure to have a professional conduct this assessment could result in the installation of an incorrectly sized air conditioner.

Install the condenser unit outside on a flat surface. Place it next to the wall nearest your furnace, but avoid placing it directly under windows if possible, as the unit makes a great deal of noise. Check to ensure the condenser is level. Build up or rake down the ground if necessary to ensure it sits flat.

Cut a hole in the side of the furnace plenum -- the sheet metal box attached to the side of the furnace -- that is slightly larger than the evaporator coil. Attach metal shelving angles or use the included evaporator shelves to the interior of the plenum so that when the evaporator fits in place there are no gaps for air to flow freely around it. Install drains or seals in the order and method specified by your manufacturer. Fit the evaporator onto the shelf and attach the cover to the plenum opening. Feed the supply lines through the holes in the cover, taking care not to kink or bend them while doing so.

Install the pipes running from the coil to the condensing unit. Two lines need to run between the two devices. The suction line is 3/4-inch copper pipe while the liquid line is made from 1/4-inch piping. Follow any instructions regarding the rise or fall of the lines as outlined in your device's documentation. For instance, some may recommend a certain pitch to the lines so there is a slight slope between the condenser and the coil. You may also have to install a trap if there is a dramatic rise in the pipe's pathway. Cut all piping smoothly and sand the ends. Don't kink the pipes in any way while running them. Press the pipes into the suction fittings, but leave the soldering for the contractor.

Run the control wiring for your air conditioner. Turn off the power at the breaker box and double check that it is truly off before you begin wiring. Run the control wiring from your compressor to the thermostat that also controls your furnace. Usually, the connections on the thermostat are labeled with a letter that indicates which color wire should be connected to that point. For instance, "G" could signify the green wire. However, some thermostats and air conditioners do not have wires properly coded to sync up. Verify the function of each colored wire in your air conditioner's instructions and check this against your thermostat's documentation to ensure you have a match before you make the connections.

Connect the wires from your condenser to a disconnect box mounted to the side of your home. Connect the wires to the appropriate terminals inside the box as indicated in the wiring diagram for your air conditioner. Then, run the wires inside the home into a junction box. Use the gauge of electrical wire specified in your conditioner's documentation and run wire from near your house's circuit breakers to the junction box. Use wire-caps to splice the wires together. Don't actually connect anything to the home power supply. Connecting the wires to your house circuitry is something that should be left for the HVAC contractor, but you can prepare by running the wiring.

Call a contractor to finish the installation. If you've done everything properly, all they have to do is braze the connection, finish the wiring and then activate the system.