Prior to doing any type of maintenance work to your air conditioning unit, you will want to make certain that the unit is turned off and that there is no power going to it. First, replace your filter. This is really the most simple but the most important tip of all. Filters are really affordable and should be changed on a monthly basis. The more dust and debris that build up on the filter, the less quality air flow your home has from the unit. Always keep extra filters on hand so that you are always able to change the dirty one.
Clean the coils on the unit as well. Dirt and debris can build up on them which causes the condenser to work harder than it should and prevents your home from getting the good cold quality air that it needs during those hot months. You can use a coil brush on them or the soft brush that comes with most vacuum cleaners to clean the coils with. Commercial coil cleaners can be used to clean the more stubborn debris from the coils and you can find this at your local hardware store.
Clean around the outside of the unit also. Rake or sweep away any leaves or limbs that have built up and that could block the free flowing of air and air circulation. You can use a rag and the vacuum to clean the blades of the blower and other parts that are exposed. The cleaner the parts are the better they will function. Remove vines or weeds that are growing around the unit also.
Check all of the lines that carry the coolant through the system. Make certain that they are flowing freely and that they are in good shape with no cracks or leaks. Replace any tubes that show broken insulation or if the insulation can be replaced, simply replace that.