Automotive Air Conditioning
Dictionary of A/C Terms and Parts
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A/C General Operation
See the description at the bottom of this page
Accumulator
Freon expands dramatically when it is heated up as it passes through the evaporator in the passenger compartment, absorbing the heat and changed into gas. The accumulator receives the freon in the gas state as it leaves the passenger compartment evaporator. It has desiccant to trap moisture so it is often called a dryer. A schrader valve is often located on the accumulator to provide for testing the low side pressure as well as an access point to install or remove freon as needed on some systems.
Alignment - Belt
The engine belts that drive the A/C compressor must be in alignment. A reason for them to be out of alignment is that the pulleys on the A/C compressor do not match with the engine pulleys. This can be due to improper installation of engine pulleys or A/C clutches as well as incorrect brackets used in mounting the A/C compressor.
Charge, Re-Charge
This describes installing freon into the A/C system. Usually charging a system means installing all of the freon into the system that it needs. Charging a system should only be done after it has been evacuated (see evacuate) and leak-tested (see leak test).

Re-charging suggests that only a portion of the freon has been lost from the system and is being replaced. Recharging a system that leaks can delay repairs, but once a system has lost all of its freon, recharging is never advisable because of contamination of air and moisture that enters the system after the freon pressure is lost.
Compressor
The compressor receives the Freon in a gas-like state and compresses it into liquid and circulates it into the condenser where the freon is cooled. The compressor is lubricated with special oil and it also has safety switches to prevent internal damage.
Condenser
The condenser converts Freon from the gas-state back to the liquid state. The condenser is a radiator-like unit made up of coils. It is often mounted in front of the car radiator. Freon comes into the condenser from the A/C Compressor and it travels on to the Expansion/Orifice Valve and then into the Evaporator.
Contamination
A/C systems can be contaminated with metal particles from the normal wear of the compressor and tiny amounts of water moisture. Contamination can cause a system to fail. Protection against contamination is provided by the filter screen on the Expansion Tube and the desiccant in the bottom of the dryer or accumulator. Other forms of contamination may be the wrong kind of oil, wrong kind of freon or other material that will interfere with the cooling system. Almost 100% of moisture is normally removed from the system when it is evacuated prior to installing freon.
Drier
Dryer is another name for the accumulator. See Accumulator. Also spelled dryer.
Evaporator
A small radiator like unit that is stationed inside the car, usually near the heater core. The Evaporator receives liquid freon into its coils. The fan inside the car circulates hot air over the evaporator coils and freon absorbs the heat and is converted to gas which then flows to the accumulator. The cooled air flows into the car.
Evacuate
In the installation or repair of your A/C you should be sure to use a vacuum pump to draw a vacuum on the entire system. Vacuum is usually measured at 29 inches. We recommend holding the vacuum for 24 hours without fluctuation (most industry sources suggest 30 minutes). The vacuum will extract any moisture from the system as well as provide some assurance against possible leaks.
Expansion Valve, Expansion Tube
Also called the orifice. This component often has a mesh screen and is found in the evaporator inlet pipe (liquid line). Its purpose is to limit the flow of the high pressure liquid freon and thereby meter the flow of refrigerant to the evaporator as a lower pressure liquid. The screen serves the purpose of trapping metal particles that break loose from the compressor or other components.
Fittings - Hose
A/C hoses are designed to control liquid and gas at high pressures and temperatures. The hoses are usually flexible and terminated with special metal fittings at the ends that prevent leaks and provide a sure seal and connection between components.
Flush
During installation or repair of A/C systems, the system should be flushed with clean special purpose fluids prior to the Evacuation and charge with new Freon. This state is critical to the success of the job and long life of the system. The process removes contamination such as particles of rubber or metal that could foul the system.
Freon R12 and R134A
The US Environmental Protection Agency has ruled that R12 Freon may no longer be used and a/c and hvac systems. Systems using R12 must be converted to R134.  Government regulations and increasing prices have made R12 a poor choice. R134A is a newer version of Freon that the EPA believes has better qualities and is environmentally friendly.

Warning. Do not mix R12 with R134a freon.

Freon is used in A/C systems because it is the best chemical available to handle transfer of heat. The trade-off in using freon is that it has to be used at higher pressures than other fluids such as alcohol or water.

General Operation
See the description at the bottom of this page
 
Hose Assembly
Various kinds of hoses are used in A/C systems. Most are specially designed for high pressure and high heat and are equipped with special metal connectors (fittings) at the ends.
 
Leak Test
A/C systems sometimes develop small leaks just like car tires do. When a leak develops the A/C freon can be lost over the course of a few minutes or a day or two. One form of leak testing is done by charging a system with a special purpose freon. When the freon escapes, it leaves a colored deposit at the point of the leak. Another form of leak testing is done by a simple pressure test, however this kind of test rarely helps locate the point of a leak.
 
Muffler
Muffler is used in the system to reduce compressor noise and vibrations from the high-pressure line.
 
Oil, Oil-charge. Compressor Oil
See PAG Oil.
 
Operation in General
See the description at the bottom of this page
Orifice Tube
See the entry for the Expansion valve.
PAG Oil.         
A/C Compressor oil, also called charge oil, or PAG oil, is special purpose oil that is designed to work with Freon. Its provides internal lubrication for the compressor. A small portion of oil circulates through the system. Some systems collect the oil at the bottom of the accumulator and return the oil directly to the compressor through a separate line.
        
Pressure Switch
The pressure switch senses internal pressures and can cycle the compressor off and back on based on minimum and maximum pressure limits.
Pressure Relief Valve
Relieves pressure from the system to protect components when internal pressures become too high.
Refrigerant
A liquid used to help transfer heat. See the description for Freon.
Radiator
A box in which metal tubes, called coils are fixed. The coils have a liquid circulated through them. The design allows for air to pass over the coils. The effect is to transfer heat from the liquid into the air. This process is used to keep the car engine cool. A similar process is used in Auto A/C systems when the gas-state freon which is super hot is circulated through the condenser (like a radiator) and the heat from the freon is removed into the air that flows over the coils.
Receiver
See accumulator.
Recharge
See Charge.
Safety Switch
Safety switches are installed at various points in the A/C system to prevent against too low or too high of a pressure or too high of a temperature. When activated, they turn off the compressor to prevent damage to the system as well as to help control its continuous operation.
Schrader Valve
This is the same kind of valve you have on your car tires and bicycle tires. It is used at one or two places in A/C systems to provide an access point to measure pressures and to remove or install (charge) freon into the system.
Sealing Caps
Metal or plastic caps that screw over the schrader valves to keep them clean.
Vacuum
A vacuum is critical to the testing and purging of the A/C system before charging it with freon. See the description for Evacuate.

General explanation of A/C Operation.

When you are hot and wipe your face with a wet towel the water evaporates taking heat away. The water vapor escapes into the air. An air conditioning system works somewhat in this way. If water were circulated through the hot-air compartment (Evaporator inside the car) the water would evaporate and turn into a vapor or gas and remove heat from the compartment. Then the gas vapor could be circulated through a larger outside radiator where it would cool and convert back into liquid water. (Many older office buildings have water towers that work in this way, but the water has to be continually replaced). A compressor-like pump would be used to recirculate the liquid water.

Automobile Air Conditioners do not use water but use a refrigerant called freon. Freon has much better ability to remove heat however it requires operation at very high pressure and so A/C compressors are used to improve the pressure as well as to circulate the freon. When the hot freon gas is compressed it returns to its liquid state. The liquid state freon circulates through the evaporator inside the car and is converted to gas, then it travels to the accumulator (also called a dryer in some applications). The accumulator allows room for the expanded freon in a gas state. The freon gas collected in the accumulator then continues on its journey back to the compressor then to the condenser mounted in front of the vehicle radiator where it is cooled and once again converted back to a liquid state with the help of the compressor. (If you look at the back of your refrigerator at home you may see a wire rack which is really a condenser - it looks a little like a radiator - that cools the fluid that keeps your refrigerator cold).

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