- Refrigerant leaks. 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 the 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.
- 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.
- Electric control failure. The compressor and fan controls 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.
- Faulty wiring. Improper or uncertified wiring is dangerous and a potential fire hazard. Bad wiring often prevents the system from getting power or can trip the circuit breaker.
- Drainage problems. When it’s humid outside, check the condensate drain to make sure it isn’t clogged and is draining properly.
- Outside fan is not working. The outside fan is responsible for transferring the heat from your home to the outside. If the fan on the outside unit doesn’t run, proper heat transfer is not taking place and the air conditioning compressor may overheat and trip the safety overload. It may even cause internal damage to the compressor.
- Outside unit not functional. This typically indicates lack of power, contactor problems or even a faulty thermostat.
- 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.
Source: US Department of Energy