Air Conditioning

Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of a home to the outside air. The machine has three main parts. They are a compressor, a condenser and an evaporator.

If we think about the words describing air conditioning, we know the words have more meaning. The air must be conditioned. Conditioning the air controls the amount of water in the air and the temperature of the air. The air can be controlled and directed to different areas of the passenger compartment. The driver can have colder air directed than the passenger. The larger the compartment the more sectionalized climate control can be performed. The air humidity can also be controlled by removing water from the passenger compartment. Humid air can cause fogging to occur and make it difficult to see out of the windows.

How AC Works

Basic Refrigeration Article

AC System Basics - Eric The Car Guy

When a liquid is changed into a gas heat is released. We can feel this occurring when we get out of the shower and the moisture which is in a liquid form on our body evaporates into a gas. We also know from previous modules that boiling points of liquids change under pressure. High pressure and low pressure can effect the liquid or gas state. If we are able to pressurize a gas and change it to a liquid, we can control the liquid or gas forms and cause liquid to gas chemical reactions.

Refrigerant

1,1,1,2-tetrafluoroethane, R-134a, Forane 134a, Genetron 134a, Florasol 134a, Suva 134a or HFC-134a, also known as norflurane, is a haloalkane refrigerant with thermodynamic properties similar to R-12 ... Wikipedia

Boiling point: -15.34°F (-26.3°C) Refrigerant has a very low boiling point. Refrigerant will be in a gas form above -26.3 degrees C. In normal climate conditions refrigerant is always a gas. We know that if we pressurize a gas we can raise the boiling point and change the gas into a liquid.

AC Compressor

The AC compressor is like an automotive engine. It is essentially a large pump that is either an electric pump or a mechanical pump driven by a belt attached to the crankshaft pulley. The AC compressor performs a lot work and it is very difficult to turn. It is a large parasitic drain on engine efficiency and fuel economy. The AC compressor is designed to compress the gas from of refrigerant intaking the gas in the suction side of the compressor. We call the suction side or intake side the low pressure side of the AC system. The low pressure gas is in a gas form and is not a liquid. A liquid can't be compressed. We can't have liquid enter into the low side of the AC compressor. The refrigerant gas is changed into a liquid as it is compressed by the compressor and sent to the AC Condenser.

The AC Condenser is located in front of the radiator. It is a heat exchanger just like the radiator, except it is only exchanging heat between compressed refrigerant and air. The condenser uses ambient air heat exchange to cool down the refrigerant furthering the formation of refrigerant as a liquid. The condenser is located on the high pressure side of the AC system, because it is under tremendously high pressure. High pressure and low heat manipulates the refrigerant boiling point.

The Orifice Tube or Expansion Valve restricts the flow of refrigerant and allows the pressure to build on the high side of the system. Image the orifice tube or expansion valve, there is more than one way to cause a restriction, is like your thumb held over the end of a garden hose. The restriction causes pressure to build up behind it. The water coming out of the hose is more like a gas because the pressure behind it is allowing depressurization as it is released from the high pressure.

Expansion Valves allow more variance of restriction and can adjust the amount of restriction and gas formation by varying size of the orifice.

Evaporator

The refrigerant leaves the expansion valve or orifice tube and enters the low pressure side of the system. The Evaporator helps change the liquid refrigerant into a gas. The evaporator is located on the low side of the system. There is dramatically less pressure and the refrigerant begins to boil and turn back into a gas. The evaporator is another heat exchanger use to take advantage of the temperature difference that occurs when a liquid is changed to a gas. The blower fan pushes the cold air through the AC air ducts.

It take time for the liquid refrigerant to completely change into a pure gas. The image below shows the low evaporation side of the AC system.

The Receiver Dryer or Accumulator

The receiver dryer and or accumulator have the same function. Receiver dryers are located on the AC high pressure side and are designed to dryer moisture or water from the refrigerant before it enters the evaporator. The accumulator prevents liquid from entering the compressor after it leaves the evaporator. Accumulator are located on the low side and receiver dryers are located on the hight side of the pressure system. Both have the purpose of accumulating liquid so it does not enter the compressor and destroy it.

Receiver drier - The receiver drier has a site glass so that mechanics can look for gas that is not suppose to be on the high side. The receiver drier is always located somewhere in the engine bay.

Accumulator

The is designed to only transfer vapor through it. The pick up for the low pressure side of the AC compressor draws in gas from the top of the accumulator.

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