1. Change or clean filters every 30 days (according to manufacture’s directions)                                                                                      ***This is the easiest and most important step to keep dust out of the duct system and to keep your equipment working at it highest efficiency.
2. Keep bushes and debris from around the outside unit. 
3. Use a garden hose to wash out debris or grass clipping from the cabinet

You can take care of basic maintenance of a central air conditioning system but you need a professional to service the compressor and to recharge refrigerant. 

Have you ever heard the term package unit or split system? A package system is one unit, heating and air conditioning contained into one machine. A split system consist of an outside unit with a compressor, condensor coil and fan. The interior evaporator coil is installed in the supply duct of a warm air furnace or air handler.

Upflow Furnace A furnace that pulls return air in from the bottom and expels warm air from the top. Downflow Furnace A furnace that pulls in return air from the top and expels warm air at the bottom. Counterflow Furnace A furnace that pulls in return air from the top and expels warm air at the bottom.