Step 1
Locate the return-air vent. It is usually in the same general area as your thermostat. This is also where the air-conditioner filter is located. Room air enters the air-conditioning unit at this return-air vent.
Step 2
Notice where the ducts go after the air is cooled. They branch out to the various rooms of the home.
Step 3
Find the registers, or small grates that aim cool air into the rooms. These are at the the ends of the ducts and are usually located in the ceiling or floor. They are smaller than the return-air vent grate. Air leaves the air conditioner at these points to cool the rooms. Air is then sucked into the return duct once again, filtering out dust and dirt.