Sealed inside an air conditioning unit is a chemical, called a refrigerant, that is converted into four different states in the unit: low pressure gas, high pressure gas, low pressure liquid and high pressure liquid. To function efficiently, the system must have a certain charge of refrigerant and must not have any contaminants within the chemical. Air conditioning systems operate at pressures over the level of atmospheric pressure, so any small leak in the system will allow some refrigerant to escape and cause a failure in the system. Therefore, you need to regularly check your unit for leaks, even small ones.
Cleaning the filter of your air conditioner is something that you should do on a monthly basis. This is no big hassle as it will take you just 5 or 10 minutes. The filter can be found on the top or bottom of the unit, and the filter on the window type air conditioning units can be found somewhere near the intake of the unit. You can always check the manual that came with your air conditioner if you are struggling to locate the filter. It is important to switch off your air conditioning at the main circuit breaker before attempting to take out the filter. Having removed it, you should let it soak in warm, soapy water for 5 to 10 minutes, and then leave it to one side to dry out. If you put it back in the air conditioning unit before it has fully dried out then it is possible that mold may build up on it. For window type air conditioning unit filters, you can also use a vacuum cleaner on it.
To do more thorough maintenance tasks you will need to call in a qualified technician, but you only have to do this every 12-18 months. They will take apart your unit and assess each of the parts in it. They will also probably re-gas the refrigerant to take it back to its optimal level. Hiring a qualified technician may cost you in the region of a $100, but that is money well spent when you compare it to the cost of having to buy a whole new unit as a result of your current one breaking down due to it not being properly maintained.