Unfortunately, your job isn't over once you've bought your unit air conditioner. You have to make sure to get your air conditioner serviced regularly or it will lose around 5% of its efficiency every year. Maintaining your air conditioner routinely will prevent you from having to spend cash later on to fix all the parts that have gone sour (aren't you glad you got an extended warranty?). It can also help you avoid irritating allergic reactions caused by dust.
Here's what you have to do to give your a/c a long lifespan:
Clean and change your filters often and keep stuff away from the unit's mechanism to keep it running at optimal efficiency.
When you plan to be away from home for the day, turn your air conditioner on a low setting (or even better, turn it off). It will ultimately save you up to $50 per year if you are conscious about doing this every time you leave your home.
Make sure that your room has tight seals around every window and door. This will maximize the energy efficiency of your home during both the summer and winter months, particularly when you're using your air conditioner.
ESPECIALLY make sure that you seal off the edges of the window where the air conditioner rests. Use foam, cardboard and duct tape, a dog, whatever you can get your hands on to make sure that the cool air blowing out the air conditioner doesn't escape right out the window.