How does an Air Conditioner work ?

                Air Conditioning depends on the laws of physics to make cold air.

We'll start at the compressor, where the refrigerant sometimes referred to as freon, gets compressed into a high pressure vapor  and pushed through the discharge line and into the condenser, where air is being drawn across it. The reason for  this air is to remove the heat out of the refrigerant and in the process condense it into a liquid. It does this because the compressed refrigerant is very hot and whether you live in a cold climate or a very warm climate the refrigerant is hotter. The laws of physics say that heat is drawn to cold. Therefore the heat inside the refrigerant gets transferred to the air and blown out the top or side of unit. When the refrigerant reaches a low enough temperature it condenses into droplets of liquid, That temperature depends on the pressure. For the sake of this article we are going to assume that you have 278 psig and that were talking about an R22 unit, your refrigerant will condense into liquid at 125 degrees. Which is the condensing temperature of R22 at 278 psi. 

                Now the refrigerant continues out of the condenser as a high pressure liquid traveling through the discharge line and into the metering device. Here the refrigerant gets metered down to a low pressure around 69 psig. There's a 209 psig drop there, and because we dropped the pressure, The temperature will also go down. The metering device whether it be a TXV (thermal expansion valve an orifice or a set of capillary tubes) acts like a garden hose nozzle, changing the steady stream of liquid into a spray mixture of vapor and liquid droplets. The reason for the spray droplets is that small droplets are more easily boiled off in its next step (the evaporator.

                After the refrigerant leaves the metering device as a low pressure mixture it enters the evaporator coil, where air from the cooled space passes over it. Now we know that heat draws to cold.

So the air moving across the evaporator coil helped by a motor and a fan whether that air be 100 degrees or 50 degrees the refrigerant is colder than that. The refrigerant pumps through the evaporator picking up heat along the way when the refrigerant reaches 40 degrees it boils back into a vapor. Even though the refrigerant is picking up heat it does not go up in temperature until it has reached the saturation point. All the heat absorbed prior to boiling is called latent heat.  When the refrigerant is totally vaporized and saturated with all the latent heat it can absorb it now starts to rise from 40 degrees, the heat absorbed after this point is called superheat. The boiling point of R22 at 69 psig is 40 degrees. Now that the air moving across the coil has dropped off its heat to the refrigerant it travels into the cooled space as colder air. Now, there's another reason for the boiling of the refrigerant other than the cooling of the air. That's to ensure the refrigerant is in a vapor state when it travels back to the compressor, to prevent damaging the compressor as pumping liquid can harm a compressor. If our refrigerant at 69 psig gets heated to 50 degrees, and we know our saturated temperature or boiling point is 40 degrees than 50-40=10 we have a 10 degree superheat. 

                Now the refrigerant is leaving the evaporator coil as a low temperature vapor. From here it continues its journey on down through the suction line (the thicker line leaving the evaporator) and enters the compressor. Here the compressor does just what it sounds like it compresses the refrigerant into a high pressure vapor. Starting the cycle all over again. The purpose of the compression is to raise the temperature of the refrigerant without adding a lot of new sensible heat. By compressing the refrigerant it will in turn rise the temperature, to a temperature hotter than the air it will encounter at the condenser. Thus allowing the heat to be transferred into the air again.