An air conditioner's job is to get rid of the heat inside your home and bring in cool air, with the help of a chemical called refrigerant. AC systems have basically five components:
- Evaporator coil (cools the air)
- Compressor (electric pump)
- Condenser coil (transfers heat)
- Expansion device
Air conditioning units have two parts: one inside your home and one outside of it. A fan in the inside unit blows air through the chilled evaporator coil, cooling your house, via air ducts. Meanwhile outside, the compressor, condenser coil and another fan vent the hot air coming off the refrigerant. The expansion valve regulates the amount of refrigerant moving between the evaporator and condenser coils.
Any of these components can experience mechanical failure. If the motor on your fan is not working, the outdoor unit can't get rid of the heat. If your compressor is damaged, the refrigerant can't circulate between the inside and outside units [source: Coolray].
Replacing some of these parts is very expensive (particularly the compressor) and may not be much cheaper than replacing the whole unit. Having a trained technician give your unit a yearly checkup should prevent premature mechanical failure.
"Residential central air conditioning units are extremely reliable, which is why homeowners often forget to perform routine maintenance on them," says Francis Dietz, vice president for public affairs for the Air Conditioning, Heating and Refrigeration Institute, says in an email. Nevertheless, these units "require attention for them to perform properly."
Which brings us to the second problem on our list.