Central air conditioning systems are built pretty rugged to withstand tough conditions, however, there are several reasons why they might fail.  If your system fails, first begin by checking any fuses or circuit breakers.  Let the unit cool down for 5-10 minutes before resetting the breakers.  If your air conditioner’s compressor stops on a hot day, the high-pressure limit switch may have been tripped; it’s best to call a professional technician in this situation.  Below are some other common reasons for air conditioner failure:

  • Refrigerant leaks.  If your air conditioner is low on refrigerant, it has a leak.  If it leaks, simply adding refrigerant is not a long term solution.  A trained technician should be called to 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.
  • Inadequate Maintenance.  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.  (In order to prevent premature compressor or fan failure, be certain to property maintain all equipment in accordance with manufacturer’s specifications.)
  • Frozen inside coil.  A frozen coil may indicate a problem with the airflow, such as restrictions caused by dirty air filters or blocked return air ductwork.  Frozen indoor coils could also be caused by low refrigerant.  A trained technician should be contacted to solve this situation.
  • Electric control failure.  The compressor and fan controls wear out, especially when the air conditioner turns on and off frequently.  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.
  • Drainage problems.  When it’s humid outside, check the condensate drain to make sure it isn’t clogged and is draining properly. 

Source:  US Department of Energy