Air conditioners need maintenance every couple years to avoid repairs. The main reason to have it checked is to verify how efficient its running. If your air conditioner runs for long periods of time its either too small, undercharged or damaged in some form. Letting your AC run like this will result in premature burn out of your air conditioner and high electricity bills. A healthy air conditioner comes on, cools within a reasonable time then cuts out when the t-stat is satisfied. Keep in mind an air conditioner only cools your home 15 - 20 degrees and that's it ! so if its 100 degrees out then you can only obtain 80 degrees max and that's only if you keep your doors, windows, and blinds shut.
Follow these tips from Central heat N cool and you will be A OK !