"First of all make your house or building structure efficient. If your attic has less than 4 inches of insulation then you need more. Almost all buildings have air leakage from the attic and the crawlspace (if you have one). Find a local contractor who has a blower door to test leakage and make sure they seal the leaks between the attic and the house. Close the drapes on your windows during the day. It is very likely that your air ducts are leaky. Air conditioners – even those with preventative maintenance contracts are likely to have problems – a new higher level diagnosis is required to ensure that the air conditioner is efficient - not just blowing cold air. The biggest common problems are insufficient airflow through the blower and the wrong amount of refrigerant in your air conditioner. You can increase the indoor airflow by avoiding the so called “high efficiency” pleated filters. A regular washable or low cost filter is fine. See Filtration and Allergies. "