The four main parts of an air conditioner are the evaporator, condenser, expansion valve and compressor. A refrigerant, fans to blow cold and hot air, filters and a thermostat are also needed to ensure your air conditioning unit works properly.
Air conditioners are divided into a cold side and a hot side. The evaporator is on the cold side. This part is made up of coils that hold the refrigerant. A fan blows over the coils, sending cold air into the room. The condenser, also filled with coils, and a second fan are on the hot side. The compressor and the expansion valve connect both sides, completing the circuit.
When the compressor pressurizes the gas refrigerant, it generates heat, which is vented to the outside with the help of that second fan. The compressor also turns the gas into a liquid, which goes to the condenser. The expansion valve connects the condenser to the evaporator, regulating the amount of liquid refrigerant that flows from the condenser into the evaporator.
The air filter usually sits next to the evaporator coil. It filters particles from the air to keep the system clean. Filters eventually get clogged with particulates and need changed periodically. Thermostats help regulate the temperature inside a home. When the preferred temperature setting is keyed in, the thermostat turns the air conditioner on and off as needed.