The first and most basic step to take to extend your air conditioners life is to change the filter. You should change it whenever it gets dirty. Depending on the use, that might range from every three to 6 months. There are some filters out there which can last up to a year. Ask someone in the hardware store for more tips.
Once a year, make certain that you inspect the evaporator coil found inside the air handler to see to it there is no dust build up More Information . When the weather condition starts to cool, you should inspect the outside of the a/c unit. You should check around the unit and see to it there is no debris on the surface of the condenser, as that will stop air movement. Also, you should check between the fins of the condenser to see that its not congested with dead bugs or pollen. Spraying the condenser with a hose will normally suffice to get rid of all the particles.
Although lots of air conditioners today make use of direct drive motors, it is a good idea to inspect the belt in the air handler. You might need to change it. If no change is required, you might only need to oil the motor bearings once a year.
It is also great to inspect the contactors and other electrical parts; most of them are found inside the condensing unit. The contactor runs the compressor, and the contacts get pitted and have to be replaced occasionally. Different manufacturers use different types of contactors, so check the manual to discover what kind you need.