A car's air conditioner cleans and dehumidifies (removes excess moisture), the outside air entering your car. It also has the task of keeping the air at the temperature you select.
The job of the air conditioning system is to "remove" the heat that makes us uncomfortable, and return the air to the car's interior in a "un-heated" condition. Air conditioning, or cooling, is really a process of removing heat from an object (like air).
A compressor circulates a liquid refrigerant and moves it from an evaporator, through a condenser and expansion valve, right back to the evaporator. The evaporator is right in front of a fan that pulls the hot, humid air out of the car's interior. The refrigerant makes the hot air's moisture condense into drops of water, removing the heat from the air. Once the water is removed, the "cool" air is sent back into the car's interior.
Sometimes we worry when we catch our car making a water puddle on the ground, but are relieved to discover that it's only water dripping from the air conditioning system's condenser (no color, no smell, and it dries!).
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The Compressor
The engine drives the compressor with a belt. In action, the compressor takes the low pressure refrigerant from the evaporator and compresses it according to speed and air temperature. The inlet side is known as the low (pressure) side and the outlet side is known as the high (pressure) side. The compressor compresses the refrigerant, and raises its temperature higher than that of the surrounding air. Then, the compressor forces the refrigerant into the condenser.
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The Condenser
The condenser is a long tube that goes back and forth through a multitude of cooling fins, quite similar to the evaporator in structure. The condenser is mounted in front of the radiator to take advantage of the forced air provided by the fan and the motion of the car.
As the highly pressurized refrigerant (vapor) flows into the condenser, it gives off heat and warms the condenser. This causes the condenser to be hotter than the forced air coming through the condenser. The condenser hands its heat off to the forced air and turns the refrigerant back into cool liquid in the expansion valve, where it heads back to the evaporator.
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The Evaporator
The evaporator is a long tube, or coil, that goes back and forth through a multitude of cooling fins. It is quite similar to the condenser in structure. The refrigerant is a liquid when it enters the evaporator. A fan blows warm air over the evaporator. The warm air causes the liquid refrigerant to boil. This means that it absorbs the heat from the warm air. Once it has absorbed the heat from the warm air, the warm air isn't warm anymore. The same blower that blows the warm air (that is now "cool" air) over the evaporator, keeps on blowing it into the interior of your car, and you have -- air conditioning!
The evaporator also removes the moisture from the air coming through its fins and turns it into water. The water just drains off, leaving a small puddle on the ground. The temperature of the evaporator coil can go from 33 degrees F to 0 degrees F. If it goes below 32 degrees F, the moisture that's supposed to drain off the coils will freeze. This makes for a very inefficient system, so a thermostatic switch is used to connect and disconnect it to the compressor as necessary.
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Expansion Valve
The expansion valve determines the correct amount of refrigerant going into the evaporator, and it lowers the pressure of the refrigerant. When the compressor starts, the expansion valve opens and the liquid refrigerant flows through a strainer in the high pressure liquid inlet. Once in the expansion valve, the refrigerant is correctly pressurized. As the evaporator calls for more refrigerant, the expansion valve allows the required amount of low pressure liquid refrigerant into the coils.
The expansion valve maintains the delicate balance between the heat load and the cooling efficiency of the evaporator.
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Compressor Relay
A capillary tube from a cycling switch lets the switch know what the temperature is in the evaporator. This switch turns the compressor on and off to keep the evaporator temperature at about 32 to 45 degrees F. The relay switch keeps moisture from freezing on the evaporator core.
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Electric Air Conditioning Fan
Sometimes an extra electric fan is placed in front of the condenser to provide an extra flow of air during warm weather, or for times when the car has to idle for a long time. You activate and deactivate the air conditioning fan when you turn it on and off at the control panel.
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Compressor Belt
The compressor is engine driven by a belt on the front of the crankshaft.
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A/C Blower Motor
The blower motor is the motor that turns the electric fan in an air conditioning or heating system.
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Air Ducts
The air ducts control the passage of hot or cold air into the interior of the car. They are operated by a control on the dash, either manually or automatically.
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Controls
Most air conditioning/heating systems have three possible air settings. One is to recirculate the air that is in the car, a second is to use only air from the outside of the car, and a third is to mix some of the outside air with the air recirculating inside the car.
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Compressor Clutch
The air conditioning compressor has an electromagnetic clutch that can engage or disengage the compressor pulley. The compressor pulley always turns when the engine is running, but the compressor only runs when the pulley is engaged to the compressor driving shaft. When this system is activated, current runs through the electromagnetic coil. The current attracts it to the armature plate. The strong magnetic pull draws the armature plate against the side of the turning pulley. This locks the pulley and the armature plate together; the armature plate drives the compressor.
When the system is deactivated, and current stops running through the electromagnetic coil, flat springs pull the armature plate away from the pulley. The magnetic coil does not turn since its magnetism is transmitted through the pulley to the armature. The armature plate and hub assembly are fastened to the compressor drive shaft. When it's not driving the compressor, the clutch pulley turns on a double row of ball bearings.
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Low Pressure Line
The low pressure line is a hose, or tube containing refrigerant that connects the evaporator to the air conditioning system's compressor. The compressor draws the low pressure refrigerant from the evaporator in through the low pressure line in order to compress it.
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High Pressure Line
The high pressure line is a hose, or tube containing refrigerant that connects the air conditioning system's compressor to the condenser. The compressor forces the compressed refrigerant into the condenser through the high pressure line.
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AC Compressor Drive Ring
Inside the air conditioner's refrigerant compressor is a drive ring made of a friction material that is mounted to both sides of the "swash" or "wobble" plate. As the swash plate rotates, the friction material pushes the ball bearings (mounted to the pistons) back and forth.
Air Conditioner Maintenance
In November of 1990, the Clean Air Act was signed into Federal law. This law requires a complete phase out of chlorofluorocarbons (commonly known as CFCs) and other ozone-depleting chemicals (ODCs) by the year 2000.
Your air conditioner uses a CFC based refrigerant, known as R-12, or freon. This law means that there won't be much R-12 left by the year 2000, and what is left will be very expensive.
This is being done because of the terrible damage CFC based refrigerant is doing to the ozone layer.
The new laws specify that all refrigerant will have to be recaptured and recycled when we have repairs made. Of course, this will take expensive and specialized equipment. Our mechanics will have to make sure that there are no leaks, and fix them if there are, before they can add any R-12 to our air conditioning systems. Naturally, this cost will be passed along to us.
Recovered refrigerant will be recycled. Capturing refrigerants and restoring them for reuse is not only environmentally sound, but mechanically safe. Each molecule of CFC in the atmosphere has a 120 year life that will destroy tens of thousands of ozone molecules. This means that a CFC molecule released in 1991 will still be damaging the ozone layer in 2100.
