One of the most common air conditioning problems is improper operation. If your air conditioner is on, windows and outside doors should be closed. If you air conditioner is a room air conditioner, the room should be isolated or open to a group of connected rooms as much as possible, so the air conditioner isn't trying to cool the entire house.
Other problems often exist in air conditioners as the result of faulty installation, poor service procedures, and inadequate maintenance.
Improper installation of a central air conditioner can result in leaky ducts and low airflow. Many times, the refrigerant charge (the amount of refrigerant in the system) does not match the manufacturer's specifications. If proper refrigerant charging is not performed during installation, the performance and efficiency of the unit is impaired. Unqualified service technicians often fail to find refrigerant charging problems or even worsen existing problems by adding refrigerant to a system that is already full.
If your air conditioner is low on refrigerant, either it was undercharged at installation, or it leaks. If it leaks, simply adding refrigerant is not a solution. A trained technician should fix any leak, test the repair, and then charge the system with the correct amount of refrigerant. Remember that the performance and efficiency of your air conditioner is greatest when the refrigerant charge exactly matches the manufacturer's specification, and is neither undercharged nor overcharged. Refrigerant leaks can also be harmful to the environment.
If you allow filters and air conditioning coils to become dirty, the air conditioner will not work properly, and the compressor or fans are likely to fail prematurely.
Electric control failure
The compressor and fan controls can wear out, especially when the air conditioner turns on and off frequently, as is common when a system is oversized. Because corrosion of wire and terminals is also a problem in many systems, electrical connections and contacts should be checked during a professional service call.
Room air conditioners feature a thermostat sensor, located behind the control panel, which measures the temperature of air coming into the evaporative coil. If the sensor is knocked out of position, the air conditioner could cycle constantly or behave erratically. The sensor should be near the coil but not touching it; adjust its position by carefully bending the wire that holds it in place.
When it's humid outside, check the condensate drain to make sure it isn't clogged and is draining properly. Room air conditioners may not drain properly if not mounted level.