Definition of Terms – Air Conditioning
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
ABSOLUTE ZERO – Complete absence of heat; believed to be -459.67°(-273.15°C).
AIR CONDITIONING – Absolute control of temperature and humidity; air conditioning in true sense used only in some laboratories and manufacturing plants where temperature and humidity control are very critical. Ordinary usage in homes, buildings, and vehicles means control of temperature and removal of moisture by condensation; more correct designation is refrigeration.
AMBIENT TEMPERATURE – Temperature of surrounding air. In air conditioning, it refers to outside air temperature
ATMOSPHERIC PRESSURE – Weight of air and liquid at various altitudes.
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B
BOILING POINT – Temperature at which a liquid changes to a vapor.
BTU – Abbreviation for British Thermal Unit. Amount of heat required to raise temperature of one pound of water 1°F. All substances are rated in relation to water as standard of measurement.
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C
CELSIUS – Thermometer scale based on O°C as freezing point of water and 100°C as the boiling point.
CHARGE – Specific amount of refrigerant by weight or volume.
COMPRESSION – Reduction in volume and increase of pressure of a gas or vapor.
COMPRESSOR – Component used to change Iow pressure refrigerant to high pressure refrigerant.
COMPRESSOR CLUTCH – An electromagnetic coupling that engages or disengages the belt-driven compressor pulley to the compressor shaft.
COMPRESSOR DISPLACEMENT – Flgure obtalned by multlplylng dlsplacement of compresor cylinder or cylinders by a given rpm, usually average engine speed.
COMPRESSOR SHAFT SEAL – A seal surrounding the compressor shaft that permits the shaft to turn without loss of refrigerant or oil
CONDENSATION – Process of changing a gas to a liquid.
CONDENSER – Radiator-type component where refrigerator gives off heat by being changed from a gas to a liquid.
CONDENSING PRESSURE – Head pressure read from gauge at high side service valve; pressure from discharge side of compressor into condenser.
CONDENSING TEMPERATURE – Temperature at which compressed gas in condenser changes from gas to a liquid. Affected directly by quantity and temperature of ram air passing through condenser.
CONDUCTION OF HEAT – Ability of substance to conduct heat (metal and glass conduct heat more readily than insulating material such as spun glass).
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D
DENSITY – Weight or mass of a gas liquid or solid.
DESICCANT – A drying agent used inside air conditioning systems to absorb and hold moisture. Silica-Gel and Molecular-Sieve are most widely used.
DISCHARGE LINE – Line connecting compress outlet to the condenser inlet.
DRIER – A device containing a desiccant placed in series, usually in the liquid line, to absorb and hold excess moisture. Usually called receiver-drier.
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E
EVACUATE – To create a vacuum to remove air and moisture in the system.
EVAPORATION – Process of changing a liquid to a gas.
EVAPORATOR – Component where liquid refrigerant is changed to a gas as it absorbs heat from inside air.
EXPANSION – Reduced pressure on liquid refrigerant lowers boiling point and refrigerant changes to a gas and absorbs heat.
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EXPANSION VALVE – Device which restricts flow of high pressure refrigerant thus lowering refrigerant pressure.
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F
FAHRENHEIT – Thermometer scale based on 32°F as freezing point of water and 212°F as the boiling point of water.
FILTER – A device used with the drier or as a separate unit to remove foreign substances from the refrigerant; installed in series in liquid line on high side of system.
FLOODED EVAPORATOR COIL – Too much liquid refrigerant in evaporator coil resulting in poor cooling.
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G
GAS – A vapor having no particles or droplets of liquid.
GAUGE SET – A set of gauges attached to the compressor service valves for testing or measuring pressure or vacuum.
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H
HEAD PRESSURE – Pressure of refrigerant from discharge reed valve through lines and condenser to expansion valve orifice.
Hg. – Chemical symbol for mercury. Inches of mercury is a measure of pressure or vacuum.
HIGH SIDE – Same as head pressure; side of system which includes vapor into condenser and liquid to expansion valve. (Also see Low Side.)
HOT GAS BYPASS LINE – Line connecting compressor outlet to evaporator inlet.
HYDROLIZING ACTION – Corrosive action within the air conditioning system induced by a weak solution of hydrochloric acid formed by excessive moisture in the system reacting chemically with the Refrigerant-12.
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J
JOULE – In air conditioning it is the metric unit of energy or heat (1J = 1055 Btu).
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K
kPa – Symbol for kilopascal which is the metric measure of pressure (1 psi = 6.895 kPa).
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L
LATENT HEAT – Amount of heat energy required to change a substance from one state of matter to another without changing its temperature.
LATENT HEAT OF CONDENSATION – Quantity of heat energy given off while changing a substance from a vapor to a liquid.
LATENT HEAT OF FREEZING – Heat given off as a liquid and changed to a solid.
LATENT HEAT OF LIQUIDATION – Heat that must be added to change a solid to a liquid.
LATENT HEAT OF VAPORIZATION – Quantity of heat energy required to change a liquid into a vapor without raising temperature of vapor above that of original liquid.
LIQUID LINE – Pipe or hose connecting condenser to expansion valve.
LOW SIDE – That portion of system from orifice in expansion valve through evaporator line or lines through compressor service valve to compressor reed valve. Also called suction side.
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M
MODULATOR VALVE – Device which limits and maintains minimum pressure in the evaporator.
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P
PRESSURE – Force upon a body, as force upon a liquid, increases the liquid’s boiling point.
PRESSURE DROP – Difference in pressure between any two points caused by friction, restriction, etc.
PSI – Abbreviation for pounds per square inch above atmospheric pressure. “G” added designates gauge pressure.
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R
RADIATION – Heat flow through space, traveling and acting much like light rays.
RAM AIR – Air that is forced around the condenser coils as the vehicle travels in a forward direction.
RECEIVER-DRIER – See “Drier.”
RECOVERY EQUIPMENT – Usually a mechanical system that consists of an evaporator, oil separator, compressor, and a condenser which draws refrigerant out of a refrigeration system and stores it in a container.
REFRIGERANT – Liquid used in refrigeration system producing cold by removing heat.
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S
SCHRADER VALVE – Spring-loaded valve similar to the tire valve, located inside the gauge hose fitting on service valves and certain controls. Will hold refrigerant in the system but can be opened by installing a special adapter with the gauge hose.
SENSIBLE HEAT – Heat which causes a change in temperature of a substance but not a change in state.
SIGHT GLASS – Window in receiver-drier or in liquid line to observe refrigerant flow.
SPECIFIC HEAT – Quantity of heat required to change the temperature of some amount of a substance.
STANDARD TON – Amount of heat released while changing one ton of 33°F (1°C) water to 32°F (O°C) ice in a period of 24 hours. 288,000 Btu (304 MJ) per 24 hours or 12,000 Btu (12.7 MJ) per hour.
STARVED EVAPORATOR COIL – Not enough refrigerant supplied to the coil, resulting in poor operation and too-low heat exchange.
SUBSTANCE – Any form of matter that can be weighed or measured; may be solid, liquid, or gas.
SUCTION LINE – Line connecting evaporator outlet to compressor inlet.
SUCTION SIDE – Low side pressure (from expansion valve orifice to intake reed valve in compressor) .
SUCTION THROTTLING – Control used to regulate flow of refrigerant from the evaporator to condenser.
SUPERHEAT – Added heat intensity to a gas after complete evaporation of a liquid; controlled by increasing pressure in air conditioning systems.
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T
TAIL PIPE – Outlet pipe from evaporator coil.
TOTAL HEAT LOAD – Human heat load plus heat entering through floor, glass, roof, and sides of vehicle.
TORQUE – Rotating power required to properly tighten a bolt or nut expressed in pounds-foot or pounds-inch (newton-meters).
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V
VACUUM – Referred to as less than atmospheric pressure and expressed as inches of mercury in Hg or kilopascals kPa.
VISCOSITY – The measure of resistance of a fluid to flow.
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W
WATT – In air conditioning, capacity is shown in Btu or Watts (1 Btu/hr = 0.293 W/hr).
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