How Air Conditioning Works
Think of an air conditioner as a machine that takes heat from your house and dumps it outside by using five interrelated parts:
There are many types of air conditioning systems that can be used in the home including window, portable, ductless and central air conditioning systems. However, they all use the following components and direct expansion refrigeration.
The refrigerant is the "blood" pumping through the air conditioner's system. It changes state from gas vapor to liquid as it collects heat from your house and rejects that heat to the outside. Pretty cool stuff (no pun intended). Refrigerant is special in that it has a very low boiling point meaning that it changes from a liquid to a vapor at low temperatures.
Think of the compressor as a sort of "heart" of the system pumping the refrigerant though all the refrigeration components in a big loop. Refrigerant enters the compressor as a low pressure warm vapor and leaves it as a high pressure hot vapor.
From the compressor, hot refrigerant vapor moves to the condenser. Here the high pressure hot refrigerant vapor is cooled by air blowing over finned condensing coils by the condenser fan as it moves through the finned coils. As the refrigerant "cools" it changes state from a hot vapor to a hot liquid at high pressure and moves onto the expansion valve. The compressor, condenser coil and condenser fan are all located in the big noisy boxy thing in your back yard often called a condensing unit
The expansion valve is really what does the work. As the hot liquid refrigerant passes through a tiny opening at high pressure in the valve on one side, it emerges as a cool low pressure mist on the other side because as a gas expands, it cools. So now we have a low pressure cold liquid mist that moves onto the evaporator coil.
The low pressure cold liquid leaving the expansion valve now runs through the evaporator coil located in the plenum of your furnace. Here the hot air of your home blows across the evaporator coil and heats it up while the cold coil cools off the air blowing across it and back into your home. As the refrigerant heats up, it boils and changes from a cold liquid and evaporates into a warm vapor. From there it moves back onto the compressor and exterior condensing unit and the cooling cycles continues.