Thermostat

• A faulty thermostat is the most likely cause of an air conditioner that continues to cool beyond the desired temperature. The thermostat allows users to set the desired temperature and then measures to see if the desired temperature has been achieved. Cleaning the thermostat and its sensors may alleviate the problem. It is also possible that the thermostat needs to be replaced.
  
  

Contactor

• A contactor is the relay that controls the air conditioner. When a desired temperature is reached the thermostat sends a signal to the contactor, which then shuts off the air conditioner. A faulty contactor may not receive or relay the signal, which will cause the AC to keep running.
  
  

Ducts

• An air conditioner that runs continuously but does not cool may be experiencing air flow problems. The air conditioner normally runs until it achieves a desired temperature. If that temperature cannot be achieved it will continue to run. This could mean that vents are blocked or that ductwork requires cleaning.