The inverter found on air conditioners means the ability of the unit to regulate its thermal power flow.

Therefore it is hard to imagine this type of device being an essential piece of an air conditioner, because it is already connected to the power line. At this point, however, a circumstantiation must be done. The inverter that is in the air conditioner is, as a matter of fact, constituted of two devices: a current rectifier and the real inverter.
So, what is the meaning in transforming the power line alternating current in direct current by the current rectifier and again in alternating current by the inverter?
To understand this " useless " job a new circumstantiation must be done: the value and the direction of the power line alternating current changes continuously, so it can be configured as a sinusoid with accurate frequency values (measured in Hz).
The " useless " job is done on account of the current frequency. The alternating current coming from the powerline (50 Hz) is initially transformed in direct current and consecutively transformed in alternating current, but with a variable frequency.
In this case it is possible to change the compressor rotation speed just changing the current frequency that supplies it: as a consequence the consumption and the freezing potentiality can be modified.
So, the best inverter air conditioners that are on the market can change their freezing capacity moving, for example, from a minimum value of 3.000 BTU/h to 23.000 BTU/h, even if they have a nominal power of 12.000 BTU/h only. It is as a car with an engine of 1.100 cc (an utility car) could change, according its needs, its piston displacement (from 250 cc - motorbike - to 2.800 cc - a sports car).
Just to complete this subject, even if all people talk about BTU, probably only a few know what BTU really means.
Generally speaking, a BTU (British Thermal Unit) is the amount of heat required to raise the temperature of one pound of water (0.45 Kg) of 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1.055 joules. In heating and cooling terms, 1 " ton " is equivalent to 12.000 BTU.