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Theory of Operation
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Here's how air conditioning works (in functional order; the components listed on the previous page):  Follow closely, because these are the key steps to a functional air conditioning system. 

Compress, heat, cool, condense, dry, expand and cool, evaporate.


First lets start with the compressor.   It's primary function is to compress and pressurize gaseous refrigerant.  It takes in cool gas into it's suction port and pressurizes it at it's discharge port.    The compressor is powered by a drive belt from the engine.  The compressor has an electrically operated engagement clutch to either turn the refrigeration operation off or on.  Output = high pressure (hot) gas.

Next is the condensor.   The condenser is located in front of the radiator (and kind of looks like a radiator too).   Through the use of cool air flow provided by the engine fan, the condensor cools the hot gas and converts it to liquid.  The liquid is still under considerable pressure and is warm, but not as hot or as high pressure as when it exited the compressor.  Output = high pressure (warm) liquid

EXPANSION VALVE SYSTEM - The exiting liquid is sent via a small tube (liquid line)to a receiver/drier (applies only to an expansion valve system).   The drier is a can with a dessicant bag inside.  It looks about the size of a soda can, and is usually located very near the condensor outlet pipe.   There is no pressure/temperature change at the receiver/drier.  Output = same as condensor, but moisture is removed by dessicant.

Now comes the magic!  As the high pressure, warm liquid exits the drier, it passes through an expansion device.  It can either be an expansion valve (which modulates refrigerant flow in an expansion valve/drier system), or a fixed expansion orifice tube in a cycling clutch/orifice tube system (which expands at the same rate all the time).  The two systems have slight have slight functional differences, mainly in how the low temperature is maintained.  Well any way, for illustration, the pressurized liquid passes through  the expansion device, the pressure is reduced considerably; hence the temperature drops also.   Output = Cold Liquid.  The following paragraph describes the expansion valve

CYCLING CLUTCH/ORIFICE TUBE SYSTEM -  The exiting liquid is sent via a small liquid line DIRECTLY to an expansion ORIFICE TUBE.  The orifice tube is fixed, therefore the proportional pressure drop across it will constant.  This type of expansion device must work in conjunction with a clutch cycling switch.  Because the pressure drop across the orifice tube is constant, the switch is used to maintain the system low pressure side in a certain operating range.  The cycling clutch switch, through various pressure changes in the system, turns the compressor off and on during normal operation.  A typical operation would have the switch turn the compressor on at about 45 psi and off at 25 degrees.   This would maintain the evaporator refrigerant at temperatures around 35-45 degrees F.

The next step is evaporator operation.  As the cold liquid exits the expansion device, it is fed to a heat exchanger type device under the dash that blows warm air from the car interior across it .  The cold liquid refrigerant is what cools the air you feel coming out of the ducts.  As the air is cooled in the heat exchanger, the liquid refrigerant is heated in the other side of the heat exchanger and then it evaporates. 

ACCUMULATOR - Only used in orifice tube system.  It contains a dessicant bag also.  The accumulator provides a similar function as the drier in the expansion valve system, but is located in the evaporator outlet instead.  This positioning allows the accumulator to collect any un-evaporated refrigerant that may still be in the liquid state, hence protecting the compressor from liquid lock damage.

The evaporated gas then returns via the LARGE tube to the compressor "suction" port to begin this whole process again.



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