Air Conditioners are now becoming a necessity, specially on tropical countries. Here in my country the temperature can go as high as 39 degrees (and there was a time that it reaches 40 degrees). Scorching hot indeed! Our air conditioner runs for more than 10 hours a day (y electric bill is the painful proof LOL). And because of running almost non stop, I noticed that the air con tends to be dirtier in a shorter period of time.
From our experience, a dirty air con does not work very efficiently. To keep it in good running condition, you must clean the air filter every week (or every 4 days if necessary). It should be thoroughly clean every 6 months by an air con technician.