Mechanical Engineering Dictionary-Refrigeration and Air-conditioning

Important Terms and their Meaning of Mechanical Engineering-Refrigeration and Air-conditioning:

ABSOLUTE HUMIDITY – The weight of the water vapour which is associated with unit quantity of air.

ABSORBER – A device for absorbing a refrigerant, a low side element in an absorption system.

ABSORPTION REFRIGERATION SYSTEM – One in which the refrigerant, as it is absorbed in another liquid, maintains the pressure difference needed for successful operation of the system.

ABSORPTION REFRIGERATOR – A plant in which ammonia is continuously evaporated from an aqueous solution under pressure, condensed, allowed to evaporate (so absorbing heat), and then reabsorbed.

ABSORPTIVITY – Ability of a material to absorb heat.

ACCUMULATOR – A steel shell partly filled with liquid refrigerant, the space above which is maintained by the compressor at a pressure corresponding to the required refrigerant temperature. The shell is placed in a suction line for separating liquid entrained in the suction gas.

ACTIVATED AMMONIA – Desiccant which operates by adsorption of water molecules. A form of aluminium oxide AlO2·

ACROLEIN – A warning agent having the formula CH2 CH CHO is often used with methyl chloride to call attention to the escape of refrigerant. The material has a compelling, pungent odour and causes irritation of the throat and eyes.

ACTUATORS – Secondary control mechanisms which function in response to the requirements of the primary group in actually controlling some part of the refrigeration system.

ADIABATIC COMPRESSION – Compression of a vapour or gas in such circumstances that there is insufficient time for any substantial exchange of heat between it and its surroundings.

ADIABATIC COOLING – Method in which paramagnetic salts are pre-cooled, and then demagnetized, thereby producing further cooling.

AERATION – A term generally employed with reference to air circulation or ventilation. In milk cooling, it refers to a method where the milk flow over refrigerated surfaces is exposed to the atmosphere.

AIR CIRCULATION – A method for natural or forced motion of air.

AIR CONDITIONING – The simultaneous control of all, or at least the first three of the following factors affecting the physical and chemical conditions of the atmosphere within a structure: Temperature, humidity, motion, distribution, dust, bacteria, or lesser degree human health or comfort.

AIR CONDITIONING UNIT – Equipment designed as a specific air treating combination, consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for maintaining temperature and humidity within prescribed limits.

AIR COOLED CONDENSERS – Condenser used to cool the refrigerant, the cooling effect depends on air drawn through tubes and fins for a good distribution of air.

AIR COOLER – The cold accumulator used in the Linde process of air liquefaction for the preliminary cooling of the air.

AIR DUCTS – Pipes or channels through which air is distributed throughout building or machinery for heating and ventilation.

AIR INFILTRATION – The in-leakage of air through cracks and crevices and through doors, windows or other openings, caused by wind pressure or temperature difference.

AIR LIQUEFIER – A type of gas refrigerating machine based on the STIRLING CYCLE, the cycle of the hot air engine.

AIR WASHER – An enclosure in which air is forced through a spray of water in order to cleanse, humidify or dehumidify the air.

ALFOL – Technical name for thin corrugated aluminium foil in narrow strips, used for heat insulation, for which it is effective by reason of the numerous small air cells formed when packed.

AMBIENT SENSOR – A temperature sensor that provides an outside air temperature signal for an automatic temperature control type air conditioning system.

AMBIENT TEMPERATURE – In a domestic or commercial system having an air cooled condenser, it is the temperature of the air entering this condenser.

AMMONIA-NH3 – One of the earliest compounds used as a refrigerant.

AMMONIA MACHINE – An abbreviation for a compression refrigerating machine using ammonia as a refrigerant. Similarly, Freon, sulphur dioxide machine etc.

ANALYSER – Device used in the high side of an absorption system for increasing the concentration of vapour entering rectifier or condenser.

ANTIFREEZE LIQUID – A substance added to the refrigerant to prevent formation of ice crystals at the expansion valve.

ATMOSPHERIC CONDENSER – A condenser operated with water which is exposed to the atmosphere.

AUTOMATIC EXPANSION VALVE – A pressure actuated device which regulates the flow of refrigerant from the liquid line into the evaporator to maintain a constant evaporator pressure.

AUTOMATIC REFRIGERATION SYSTEM – One which regulates itself to maintain a definite set of conditions by means of automatic controls and valves usually responsive to temperature or pressure.

BASIC REFRIGERATION CONTROL – Device that starts, stops, regulates and/ or protects the refrigeration system and its components.

BAUDELOT EVAPORATOR – An open type of cooler in which the liquid to be cooled flows from distributing troughs or headers over a cooling surface consisting of sets of grids or a pair of stamped corrugated metal sheets forming channels.

BLEEDER – A pipe sometimes attached to a condenser to lead off liquid refrigerant, parallel to the main flow.

BRINE – Any liquid cooled by the refrigerating system and used for the transmission of heat.

BRINE SYSTEM COOLING – Any system whereby brine, cooled by a refrigerating system, is circulated through pipes to the point where the refrigeration is needed.

BUTANE – A hydrocarbon, flammable refrigerant used to a limited extent in small units.

CALCIUM CHLORIDE – A chemical having the formula CaCl₂ which is in granular form is used as drier. Soluble in water.

CALCIUM SULPHATE – A solid chemical of the formula CaSO4 which may be used as a drying agent.

CAPACITY – In a refrigerating machine, it is the heat absorbing capacity per unit time, usually measured in ton or kcal/hr.

CAPILLARY – A tube with a very small inside diameter, its diameter and length control the flow of the refrigerant; dividing point between the high side and the low side of the system.

CARBON – One of the elements used in refrigeration.

CARBONDIOXIDE – One of the earliest compounds used as a refrigerant.

CARBON TETRA CHLORIDE – A liquid having the formula CCl₄ (also known as carbona) which is non -inflammable solvent used for removing grease and oil and loosening sludges.

CENTRIFUGAL COMPRESSOR – A compressor in which the necessary increase in the pressure of the refrigerant vapour being obtained by imparting a high velocity to it by the rotation of an impeller.

CHANGE OF STATE – A change from one state to another as from liquid to solid, from liquid to gas etc.

CHARGE – The amount of refrigerant in a system.

CHARGING CYLINDER – A cylindrical container for refrigerant that has a calibrated sight glass so that the mechanic can measure the flow of refrigerant into the air conditioning system.

CHLORINATED FLUORO CARBON – The chemical family into which air conditioning refrigerants such as refrigerant 12 fall.

CIRCUITS – The flow of a refrigerant through separate rows of tubes rather than through one single tube.

CLEARANCE VOLUME EFFICIENCY – Ratio of the weight of the refrigerant circulated by a compressor having no losses except that due to clearance, to the weight circulated by a perfect machine.

CLOSED SYSTEM – Chilled water from the flash tank is pumped through a coil to cool air and is then returned to the flash tank.

COEFFICIENT OF PERFORMANCE – The ratio of the refrigerating effect to the heat equivalent of the indicated horse power of the refrigerant compressor.

COIL – Any cooling element made of pipe or tubing.

COLD STORAGE – A trade or process of preserving perishables on a large scale by refrigeration.

COMFORT CHART – A psychrometric chart; strictly a chart showing the effective temperatures.

COMPOUND COMPRESSION – In compound or multistage compression, the refrigerant is compressed through part of the pressure range in one compressor (or in one stage of a multistage compressor) and then passed to a second compressor, or stage, of smaller swept volume, which carries the compression further.

COMPOUND GAUGE – A typical low pressure test gauge, which has a scale that indicates both pressure and vacuum.

COMPRESSOR – A device that takes a refrigerant vapour at a low temperature and pressure and compresses it to a lower volume and thereby raises it to higher temperature and pressure.

COMPRESSOR CRANKSHAFT SEALS – Prevent air from entering the compressor, and oil and refrigerant from escaping.

COMPRESSION RATIO – The ratio of two pressures, the absolute discharge pressure divided by the absolute suction pressure.

COMPRESSION SYSTEM – A refrigerating system in which the pressure imposing element is mechanically operated.

CONCENTRATORS – Evaporate excess water from brine which has been diluted by melted ice and frost.

CONDENSATION – Process by which a vapour is changed into a liquid without changing temperature. Condenses the hot, high pressure refrigerant vapour from the compressor to a warm, high pressure liquid which flows to the receiver dehydrator.

CONDENSER (general) – That part of the refrigeration system in which the refrigerant condenses and in so doing gives off heat.

CONDENSER DUTY – Amount of heat transferred in a given time from the refrigerant to the cooling medium in the condenser.

CONSTANT PRESSURE VALVE – An automatic expansion valve that holds the pressure at a constant level regardless of the load.

CONSTANT TEMPERATURE VALVE – A valve responsive to temperature of thermostatic bulb, of the throttling type, located in suction line of an evaporator to reduce refrigerating effect on coil to just maintain a desired temperature.

CONTAINER CAPACITY – The ability of a container to hold the material the quantity of material which may safely be contained in a container.

COOLING UNIT – A specific air treating combination consisting of means for air circulation and cooling within the prescribed temperature limits.

COOLING WATER – Water used for condensation of the refrigerant.

COPPER PLATING – Formation of a film of copper usually on compressor walls, pistons or discharge valves.

CRYOGENICS – Science of producing and applying temperature below –250° F.

CRYOGENIC SUPER CONDUCTOR SYSTEM – Uses helium to cool conductors to within a few degrees of absolute zero where they offer no electrical resistance.

CRYOHYDRATE – A eutectic brine mixture of water and any salt, mixed in proportions to give the lowest temperature.

CYCLE OF REFRIGERATION – A complex course of operation of a refrigerant back to the starting point, measured in thermodynamic terms, also used in general for any repeated process for any system.

CYCLING CLUTCH CONTROL SYSTEM – One in which the compressor is run intermittently to maintain a desired temperature.

DEGREE DAY – A unit, based upon temperature difference and time, used in specifying the nominal heating load in winter.

DEFROSTING – Removal of accumulated ice from the cooling unit.

DEFROSTING CYCLE – A cycle which permits cooling unit to defrost during off period.

DEFROSTING EVAPORATOR – Unit in which frost accumulates on cooling coils when the compressor operates and melts after the compressor shuts off.

DEHUMIDIFY – To remove water vapour from the atmosphere, to remove water or liquid from stored goods.

DEHYDRATOR – A device used to remove moisture from the refrigerant.

DESICANT – Material used in a drier to trap moisture from the refrigerant. Also called drying agent.

DEWAR FLASK – A container which consists of alternate layers of radiation shields and spacer material in high vacuum.

DEW POINT – That temperature at which the air (space) becomes saturated with water vapour. When the air is cooled to the dew point, water vapour can condense into liquid form (provided its latent heat is removed).

DEW POINT THERMOSTAT – A thermostat used in such a way as to control humidity.

DICHLORODIFLUORO METHANE – The chemical compound known as Freon 12 or R -12.

DIELECTRIC – Thin insulating material separating two conductor plates in a capacitor.

DIFFERENTIAL – Difference of temperature or pressure between the on and off operation of the control.

DIRECT EXPANSION – A system in which the evaporator is located in the material or space refrigerated or in air circulating passages communicating with such space.

DIRECT EXPANSION EVAPORATOR – One that contains only enough liquid to continue boiling as heat is absorbed by it.

DISCHARGE SHUT OFF VALVE – A manual valve installed on the compressor, which controls the flow of the refrigerant from the cylinder head of a compressor to the discharge line.

DISPLACEMENT, ACTUAL – The volume of gas at compressor inlet conditions actually moved in a given time.

DISPLACEMENT, THEORETICAL – The total volume displaced by all the pistons of a compressor for every stroke during a definite interval, usually measured in cubic metre per minute.

DOMESTIC REFRIGERATOR – A refrigerator for home use.

DOUBLE ACTION PISTON COMPRESSOR – A type of compressor used in automotive A/C systems in which an axial swash plate pressed to the shaft is used to drive the pistons.

DOUBLE EFFECT EVAPORATOR – An arrangement of two evaporators such that the vapour from No. 1 is carried over into the tubes of No. 2. The drain from the first evaporator is led to the hot well and the drain from the second evaporator is led to the fresh water condenser and there cooled down to be used by the passengers.

DOUBLE THICKNESS FLARE – Indicates that the flare thickness of a tube end is made up of two thicknesses of tubing.

DRIER – Device designed to remove moisture from a refrigerant.

DRIERITE – Desiccant which operates by chemical action.

DRY BULB TEMPERATURE – The actual temperature of the air as measured by an ordinary thermometer.

DRY ICE – Frozen carbon dioxide, sold under the trade names, such as CARDICE and DRICOLD. This has the property of passing directly from the solid to the gaseous state without becoming a liquid.

DRY TYPE EVAPORATOR – An evaporator of the continuous tube type where refrigerant from a pressure reducing device is fed into one end and the suction line is connected to the outlet end.

EBULLATOR – A device inserted in flooded evaporator tubes to prevent evaporator from being oil bound.

EJECTOR – A device which utilizes static pressure to build up a high fluid velocity in a restricted area to obtain a lower static pressure at that point so that fluid from another source may be drawn in.

ELECTROMAGNETIC CLUTCH MECHANISM – Device which when engaged, turns the compressor shaft to start piston movement.

ELECTROPNEUMATIC AIR CONDITIONING SYSTEM – A system, in which an adjustable sensing device permits the selection of comfortable conditions, has two thermistor to monitor and sense both the outside air and the air in the passenger compartment.

ELIMINATOR PLATES – Protect refrigerated spaces and air from brine spray.

EMULSIFICATION – Formation of an emulsion, i.e., a mixture of small droplets of two or more liquids which do not dissolve with each other.

EQUALIZERS – Connections used with thermostatic expansion valves when the superheat setting of the expansion valve cannot control the amount of refrigerant which flows through the coil.

EQUILIBRIUM – Condition existing at saturation, the molecules of the refrigerant in liquid state are changing into the vapour state as rapidly as vapour molecules are changing into the liquid state.

EUTECTIC POINT – The lowest freezing point (temperature obtainable) when the concentration of solid in a solution is increased gradually.

EUTECTIC SOLUTION – A solution which can be made so that it freezes and melts at a specific temperature.

EVACUATE – To discharge refrigerant from the air conditioning system into the atmosphere or a holding tank, and then to vacuum pump the system in order to boil away any moisture.

EVAPORATOR – Device in the low pressure side of a refrigeration system through which the unwanted heat flows; absorbs the heat in the system in order that it may be moved or transferred to the condenser.

EVAPORATOR (automotive ac system) – Device that cools, dehumidifies, and takes the pollen and dust from the air before it enters the passenger compartment.

EVAPORATOR DUTY – The amount of heat which can be removed by the evaporator i.e., the amount of refrigeration accomplished.


SYSTEM – Uses either a suction throttling valve, a pilot operated absolute valve, or an evaporator pressure regulator valve to control evaporator temperature.

EVAPORATOR REGULATOR VALVES – Provide independent temperature control for each evaporator.

EXPANSION VALVE – Metering device which provides a restriction so that there is a steady flow of refrigerant and also maintains the difference of pressure required to change the state of the refrigerant.

FLARING – Method of forming or preparing the ends of tubing to connect them directly with or through the use of fittings.

FLEXING DISC VALVE – One type of valve commonly used in compressors. It is a one way valve.

FLOODED EVAPORATOR – One that is full of liquid refrigerant at all times. Additional liquid is permitted to enter only to replace that which boils away.

FREEZER BURN – Surface damage due to excessive drying during freezing.

FREON 12 – Refrigerant used in automatic air conditioners. Also known as Refrigerant -12 and R-12.

FROST HEAVE – Refers to the movement of ground as a result of being frozen because of insufficient insulation underneath a cold store.

FUSES – Devices used for protection of electrical circuits, either cartridge or plug type.

GAS VOLUME CONTROL – Used to regulate the amount of gas needed to produce certain desired temperatures and conditions in domestic absorption automatic control refrigerators.

GROUNDING – Protection against static charges which sometimes build upon operating equipment.

HALIDE LEAK DETECTOR – Operates on acetylene to detect vapour leaks of halogen refrigerants.

HEAT OF RESPIRATION – Heat given off by cargo.

HELIUM LIQUEFIER REFRIGERATOR – The complete system for liquefying helium.

HERMETIC COMPRESSOR – The compressor unit in which the motor and the compressor are manufactured as a single self contained unit housed within a casing, the electric motor is in contact, therefore with the refrigerant.

HIGH PRESSURE CUTOUT – A pressure operated switch which stops the machine on the rise of pressure to a level approaching danger, and usually has to be reset by hand.

HIGH SIDE FLOAT – Metering system which locates the float and needle valve on the high pressure side of the refrigeration system.

HOLD OVER PLATES – Containers that hold the eutectic and provide refrigeration.

HUMIDITY – Moisture in air.

HUMIDISTAT – Operating control which reacts to variation in humidity.

ICE MAKING CAPACITY – Ability of a refrigerating system to make ice, starting with water at room temperature.

INDICATED HORSE POWER – Rate at which work is usefully expended in the compressor i.e., actually utilized in compressing the refrigerant vapour and expelling it from the compressor.

INDUCTIVE DEVICE – Designed to convert electrical energy to magnetic and then to mechanical energy.

INSULATION – Any material that effectively slows down the transfer of heat.

INSULATORS – Materials that normally deter the flow of electrons.

LATENT HEAT – Heat energy which causes a change of state without any change of temperature.

LIMITING CONTROLS – Safety controls.

LIQUID LINE CHARGING VALVE – Used for high side charging.

LIQUID LINE SHUT OFF VALVE – Manual valve installed in liquid line near condenser well to shut off flow of refrigerant between the condenser and the liquid line.

LIQUID NITROGEN SHIELD – At room temperature, it can absorb any heat leakage from outside and reduce temperature between itself and cryogenic refrigerant surrounding the cable.

LIQUID NITROGEN SYSTEM – A non-mechanical refrigeration system for transport use.

LITHIUM BROMIDE – Used in combination with water in absorption cooling systems.

LOW PRESSURE CONTROL – An electric switch responsive to pressure, connected into the low pressure part of a refrigeration system. Usually closes at high and opens at low pressure.

LOW PRESSURE CUTOFF SWITCH – Senses system pressure only, wired in series with the magnetic clutch.

LOW SIDE FLOAT – Metering system which locates a float in the low pressure side of the refrigeration system.

LOW TEMPERATURE TRANSPORT – Refrigerated trucks that maintain temperatures in the range of 0°C and below.

MANIFOLDING – In direct expansion or dry evaporators, the method of circulating the refrigerant through separate rows of tubes.

MANUAL CONTROL SYSTEM – An A/C system in which the driver of an automotive vehicle selects heating and cooling by use of a lever which mixes warm and cold air to desired temperature.

METERING DEVICES – Restrict the flow of the refrigerant from the high to the low side, regulate the flow of the refrigerant according to the needs of the system.

METHYLENE CHLORIDE (CH2Cl2) – A halogenated hydrocarbon which is considered a safe refrigerant.

MODULATING CONTROLS – Provide for variations by steps as contrasted to the off and on operation of the refrigeration systems with ordinary controls.

MODULATING THERMOSTAT – Used to operate dampers on DX coils and valves for varying the flow of chilled water.

MODULATING THERMOSTATIC EXPANSION VALVE – Varies the capacity of the valve in response to variations in load on the system.

MOISTURE VAPOUR SEAL – A tight barrier placed outside the insulation to prevent pushing of moisture through the insulation by vapour pressure.

MULTIPLE UNIT INSTALLATION – One in which two or more evaporators in different refrigerators are operated from one compressor, or vice versa.

NONFLEXING RING PLATE TYPE VALVE – One type of valve commonly used in compressors.

NONFROSTING EVAPORATORS – Use only the thermostatic expansion valve type of refrigerant control, operate at a temperature close to freezing.

NONMECHANICAL REFRIGERATION SYSTEMS – Those that obtain the required high and low pressures by some method other than a mechanical compressor.

OIL FAILURE RELAY – An oil pressure switch inserted in the compressor lubricating system and wired to shut down the machine in the event of an oil failure.

OIL SEPARATOR – Device used to separate oil from the refrigerant gas, returning the oil to the compressor and allowing the refrigerant to continue on its circuit through the refrigerating system.

OPEN SYSTEM – Chilled water is sprayed into the air to be cooled and it is then collected in the air washer tank and returned to the flash tank and is again cooled.

OPERATING CONTROLS – Sensitive to changes in the desired conditions such as temperature (or its related pressure) and humidity.

pH VALUE – Logarithm to base 10 of the reciprocal of the concentration of hydrogen ions. Measure of the acidity or alkalinity of a solution.

PRESSOSTAT – An automatic switch connected by a small bore tube to the suction of the compressor, stopping the latter when the pressure falls to a certain value and starting it again after a definite rise in pressure.

PRESSURE RELIEF VALVE – Used to minimize the possibility of explosion when air temperature surrounding a refrigeration system may rise to a point where it causes the pressure of the refrigerant gas to increase to a danger point.

PRIMARY REFRIGERANT – A substance used as the working fluid in the vapour compression cycle, as distinct from a secondary refrigerant, which in some cases is used as an intermediate conveyor of heat between the substance to be cooled and the primary refrigerant.

PSYCHROMETRIC CHART – A graph, the coordinates of which are usually either dry bulb temperature and absolute humidity, or enthalpy (total heat) and absolute humidity. Families of lines are there showing constant dry bulb temperatures, wet bulb temperatures, enthalpies, absolute humidities, relative or percentage humidities and specific volumes.

PURGING – A method of removing air and moisture from a refrigerating system by means of the refrigerant gas pushing some of the air ahead of it and out of the system.

REFRIGERANT – Substance which is circulated in a refrigeration system to transfer heat.

REFRIGERANT FAMILY – Safest group of refrigerants produced by manipulating the atoms of carbon tetrachloride with those of fluorine and hydrogen.

REFRIGERATING CAPACITY – The ability of a system to remove heat as compared with the cooling effect produced by the melting of ice, expressed as a rate of heat removal, kcal/ hr or tons/ 24 hrs.

REFRIGERATION SYSTEM – The part of the refrigeration/ air conditioning system that includes compressor, condenser, evaporator, control valves and switches and tubing. It absorbs the heat from air in the duct housing/space and transfers it to the outdoors.

RELATIVE HUMIDITY – The percentage of moisture in the air compared with the maximum amount that the air can hold, at the prevailing temperature. Also expressed as the ratio of the pressure of the water vapour present to the maximum possible water pressure at the prevailing temperature.

RESISTIVE CRYOGENIC SYSTEM – Uses nitrogen to cool the electrical conductors to temperatures where their electrical resistance is very low.

REVERSE CYCLE REFRIGERATION – Uses rejected heat to produce warmth.

ROTARY COMPRESSOR – Compressor which consists of a cylindrical casing containing a shaft whose axis is eccentric to that of the cylinder, the shaft carries a rotor having radial slots in which blades slide and the tip of the blades press against the casing by their inertia or with the aid of springs.

SAFETY HEAD – Unit which is not fixed to the top of the cylinder but is held down by heavy springs and allows the passage of liquid refrigerant or oil, which it does by lifting bodily whenever the pressure in the cylinder becomes abnormally high.

SEALED UNIT – The compressor unit in which the compressor, usually rotary, and the driving motor are contained within a welded steel shell.

SECONDARY REFRIGERANT – Chilled liquid like water which is circulated to distant units where the air is to be cooled in individual rooms.

SEMI HERMETIC COMPRESSOR – The compressor unit in which the motor and compressor are a single unit, but the motor is detachable from the compressor and therefore capable of field repairs.

SHELL AND COIL CONDENSER – A cylindrical shell, usually vertical, containing a water coil, and within the shell the refrigerant is condensed.

SHELL AND TUBE EVAPORATOR – An evaporator having a cylindrical casing, containing a number of tubes through which the liquid to be cooled flows and the refrigerant is contained within the casing.

SHRADER VALVE – A spring loaded valve through which a connection can be made to a refrigeration system, also used in vehicle tyres.

SIGHT GLASS – In a car air conditioner, a viewing glass or window set in the refrigerant line, usually in the top of the receiver dehydrator, the sight glass allows a visual check of the refrigerant passing from the receiver to the evaporator.

SILICA GEL – Desiccant which operates by adsorption of water molecules.

SINGLE THICKNESS FLARE – The part of the tubing that forms the flare is the thickness of the tubing.

SPRAY HEADER – Perforated pipe mounted along the ceiling of the cargo compartment of a transport.

STEAM JET SYSTEM – Uses a device in which the extremely rapid flow of a vapour through a narrow tube reduces the pressure and permits evaporation of a liquid, produces a cooling effect.

STRONG AQUA – An ammonia and water solution with a concentration of almost 30 percent ammonia, used in ammonia absorption cooling system.

SUCTION LINE – Runs from evaporator to compressor, returns the heat laden gases from the evaporator.

SUCTION SERVICE VALVE – Manual shut off valve installed on the compressor. Also called suction valve.

SUCTION THROTTLE VALVE – The compressor is in continuous operation and the valve is opened and closed by sensing the actual evaporator operating pressure.

SULPHURDIOXIDE – An old refrigerant that was used to recharge units.

SUPERHEATING – The rise in temperature resulting from the addition of heat to the refrigerant vapour either in the evaporator or in the suction line.

SUPERHEAT SWITCH – Designed to protect the A/C system compressor against damage when the refrigerant charge is partially or totally lost.

SUPER INSULATION – Alternate layers of radiation shields and spacer material operating in a high vacuum.

SURGE CHAMBER – A drum or container into which liquid enters from the metering device in order to recirculate the refrigerant in a flooded evaporator.

SWAGING – A means of shaping copper tubing so that two pieces may be joined without the use of a fitting.

TEMPERATURE CONTROL – An electric switch responsive to temperature of thermostatic bulb or element.

TERMINAL DEWARS – Insulated containers used to prevent heat transfer and permit the individual conductor phases to be connected into thermally and electrically graded pot head assemblies.

THERMAL LIMITER FUSES – Designed to protect the A/C system compressor against damage when the refrigerant charge is partially or totally lost.

THERMOELECTRIC REFRIGERATION – Depends upon passing electrical energy to a couple through two dissimilar semiconductors.

THERMOPNEUMATIC AIR CONDITIONING SYSTEM – System which uses the mechanical principles of the thermostat to monitor vacuum motors which adjust the air valves and switches.

THERMOSTAT – An automatic switch, the opening and closing of which is actuated by change of temperature.

THERMOSTATIC EXPANSION VALVE – Control valve which maintains constant superheat in the evaporator, also used for the temperature control, operates on increased pressure resulting from a rise in temperature. Also called THERMOSTATIC VALVE.

THROTTLING VALVE – Dampens fluctuations of pressure gauge and provides a way to close off the port entirely.

TON REFRIGERATION – Ton refrigeration (TR) is that rate of removal of heat which would transform water at 0°C into ice at the same temperature at the rate of one ton in every 24 hours.

VACUUM PUMP – A device used to evacuate systems in preparation for charging them with a refrigerant.

VALVE RETAINER – A device which limits the lift of the valve.

WATER CONTROL VALVE – Used in A/C systems to regulate the flow of coolant to the heater core.

WATER ICE REFRIGERATION SYSTEM – Heat is absorbed as ice melts, producing the desired cooling effect.

WET BULB TEMPERATURE – The temperature read, by a wet bulb thermometer, this is an ordinary thermometer the bulb of which is wetted by being surrounded by a sheath of muslin kept wet by pure water.

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