subject: Automatic Air Conditioning - What Is It? [print this page] All air conditioning systems work in the same basic way, relying upon the principles of evaporation, condensation, compression and expansion, and consist of the same seven major components: the compressor, condenser, recover-drier, orifice tube or expansion valve, evaporator, hoses and of course refrigerant.
The refrigerant which is now HFC-134a ( R-134a ), boils at around-15.9F, which means it is usually a gas under standard atmospheric pressure. One of the rudiments on which an A / C system operates is Latent Heat of Evaporation, suggesting that the refrigerant must be in a position to vaporize, so it must first become a liquid. If you are inexperienced in the Latent Heat Principle, it is the same concept as how sweat helps control your body temperature on a sunny day.
When you sweat, the moisture evaporates from your skin, absorbing heat in the process and creating a cooling sensation. With R-134a, to raise the boiling point high enough for the refrigerant to condense to a liquid at more realistic ambient temperatures, it must be highly pressurized.
The A / C system is a regular loop that is split up into a high pressure side and low pressure side by the compressor. The high pressure made by the pumping of the compressor pushes the now heated and pressurised gaseous refrigerant thru a hose into the condenser, where a lot of the heat causes the refrigerant to condense into a liquid state. The still-highly-pressurized liquid then flows into the recover-drier, which has a filter to get rid of any waste in the system as well as desiccant material to get rid of any moisture or impurities from the refrigerant. ( Moisture mixed with refrigerant can form a corrosive acid )
The purified liquid refrigerant flows through the A/C hoses and into the cabin of the car, where it is then forced through a small orifice, either in the form of a fixed orifice tube or thermal expansion valve. the resulting fine mist that is metered by the valve (think of a finger over the end of a hose) blows into the evaporator located in the heater box under the dash. The drop in pressure caused by the expansion valve is sufficient to cause the refrigerant to vaporize as it moves into the evaporator, absorbing a good deal of heat in the process.
A fan located in the heater box blows ambient air across the now chilled evaporator, which absorbs heat from the air, and the resulting cooled air blows through the vents into the cabin. Because the cooled air has less capacity to hold moisture, the evaporator also dehumidifies the air.
Condensation develops on the evaporator and the water drips away through a drain in the evaporator box and causes the puddles usually seen under vehicles with the A/C running.
Depending upon the system design, as the gaseous refrigerant is sucked back toward the compressor, there may also be an accumulator attached to the outlet of the evaporator that serves to ensure no liquid refrigerant or moisture makes its way to the compressor.
And that's about it when it comes to learning how the A/C in your car works.
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