Dirty Filter

• If you haven't changed your filters in a while, you are putting your air conditioning system and your entire home at risk. Air filters screen out impurities in the air while allowing free airflow throughout the system. If the filter is neglected for long periods of time, it can become so clogged that air cannot pass through it. When this happens, air will stop moving through the air conditioning system entirely. It will also allow damaging dust and grime to build up on the cooling coils that could lead to overheating or icing of the outdoor unit. The air filter should be changed monthly under heavy use. Although most filter manufacturers say they are good for 90 days, filters should be changed more frequently to maintain maximum efficiency in the cooling system.
  
  

Blower Motor Malfunction

• The central unit forces air through the ducts en route to the registers to cool your home. Fans generate the forced air in the outside condenser, as well as the indoor air handler. Each fan has its own motor. If the blower fans are not working properly, the unit will cool the air but have no way of delivering it. You will need to get an HVAC repair technician to pull out any bad blower motors and replace them immediately to resolve the problem.
  
  

Duct Blockage or Leaks

• Your air conditioner may be working properly, but the ducts that guide the cool air into each rooms may be blocked or leaking. Debris or possibly animals could find their way into the ducts and cause trouble by blocking off the main airflow route into the home from outside or between the air handler and the rest of the house. Professional duct cleaning is the only thorough way to make sure the ducts are clear and will allow air through. It is also possible that the ducts have been damaged and are leaking, or that a main duct has become separated from the rest of the system, causing a major air pressure leak.
  
  

Power Supply

• The outside condenser may be working normally, but the air handler that forces the air through the registers may be turned off. Most systems have a power switch on the air handler that could have been bumped accidentally. Check to see if it is turned on. If it is, it could also be a tripped breaker, especially if the air handler is on its own electrical circuit.