6666278 Glossary of Technical Terms Steps

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GLOSSARY OF TECHNICAL TERMS

HVAC STEPS SAFE

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GLOSSARY OF TECHNICAL

TERMS

ABSOLUTE HUMIDITY: Amount of moisture in

the air, indicated in grains per cubic foot.

ABSOLUTE PRESSURE: Gauge pressure plusatmospheric pressure (14.7 Ibs. per sq. in.).

ABSOLUTE TEMPERATURE: Temperaturemeasured from absolute zero.

ABSOLUTE ZERO TEMPERATURE: Temperatureat which all molecular motion ceases. (-460 F. and -

275 C.)

ABSORBENT: Substance which has the ability totake up or absorb another substance,

ABSORPTION REFRIGERATOR: Refrigerator

which creates low temperatures by using the

cooling effect formed when a refrigerant isabsorbed by chemical substance.

ACCELERATE: To add to speed; hasten progress

of development.

ACCUMULATOR: Storage tank which receives

liquid refrigerant from evaporator and prevents itfrom flowing into suction line.

ACID CONDITION IN SYSTEM: Condition in

which refrigerant or oil in system is mixed withfluids which are acid in nature.

ACR TUBING: Tubing used in refrigeration which

has ends sealed to keep tubing clean and dry.

ACTIVATED ALUMINA:Chemical used as a drieror desiccant.

ACTIVATED CARBON:Specially processed carbon

used as a filter-drier; commonly used to clean air.

AD1ABATIC COMPRESSION: Compressingrefrigerant gas without removing or adding heat.

ADSORBENT: Substance which has property tohold molecules of fluids without causing a chemical

or physical change.

AGITATOR: Device used to cause motion in

confined fluid.

AIR CLEANER: Device used for removal of

airborne impurities.

AIR COIL: Coil used with some types of heatpumps which may be used either as an evaporator

or as a condenser.

AIR CONDITIONER: Device used to controltemperature, humidity, cleanliness, and movement

of air in conditioned space.

AIR-COOLED CONDENSER:Heat of compressionis transferred from condensing coils to surrounding

air. This may be done either by convection or by afan or blower.

AIR COOLER: Mechanism designed to lower

temperature of air passing through it.

AIR CYCLE, AIR CONDITIONING:System which

removes heat from air and transfers this heat to air.

AIR DIFFUSER:Air distribution outlet designed to

direct airflow into desired patterns.

AIR SENSING THERMOSTAT:Thermostat unit in

which sensing element is located in refrigeratedspace.

AIR SPILL-OVER: Refrigerating effect formed by

cold air from freezing compartment in refrigeratorspilling over, or flowing into normal storage- area of

refrigerator.

AIR WASHER: Device used to clean air, whichmay increase or decrease humidity.

ALCOHOL BRINE: Water and alcohol solutionwhich remains a liquid at below 32 F.

ALLEN-TVPE SCREW: Screw with recessed headdesigned to be turned with hex shaped wrench.

ALTERNATING CURRENT (AC): Electric current

in which direction of flow alternates or changes. In60 cycles current direction of flow reverses every

120th second.

ALTITUDE ADJUSTMENT:Adjusting refrigerator

controls so unit will operate efficiently at altitude inwhich it is to be used.

AMBIENT TEMPERATURE: Temperature of fluid

(usually air) which surrounds object on all sides.

AMMETER: An electric meter used to measurecurrent, calibrated in amperes.

AMMONIA: Chemical combination of nitrogenand hydrogen (NH^). Ammonia refrigerant is

identified by R-117.

AMPERAGE: Electron or current flow of one

coulomb per second past given point in circuit.

AMPERE: Unit of electric current equivalent to

flow of one coulomb per second.

AMPERE TURNS:Term used to measure magneticforce. Represents product of amperes times number

of turns in coil of electromagnet,

AMPLIFIER: Electrical device which increases

electron flow in a circuit.

ANEMOMETER:Instrument for measuring the rate

of flow of air.


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ANHYDROUS CALCIUM SULPHATE: Drychemical made of calcium, sulpher and oxygen(CaSO4).

ANNEALING: Process of heat treating metal to

obtain desired properties of softness and ductility(easy to form into new shape).

ANODE: Positive terminal of electrolytic cell.

ARMATURE: Revolving part in electric motor orgenerator.

A.S.A.: Formerly, abbreviation for AmericanStandards Association. Now known as United States

of America Standards Institute.

ASPECT RATIO: Ratio of length to width of

rectangular air grille or duct.

ASPIRATING PSYCHOMETER: A device which

draws sample of air through it for humiditymeasurement purposes.

ASPIRATION: Movement produced in a fluid bysuction.

ATMOSPHERIC PRESSURE: Pressure that gasesin air exert upon the earth; measured in pounds per

sq. inch,

ATOM: Smallest particle of element that can exist

alone or in combination.

ATOMIZE: Process of changing a liquid tominute particles, or a fine spray.

ATTENUATE: Decrease or lessen in intensity.

AUTOMATIC DEFROST: System of removing iceand frost from evaporators automatically.

AUTOMATIC EXPANSION VALVE (AEV):Pressure controlled valve which reduces high

pressure liquid refrigerant to low pressure liquid

refrigerant.

AUTOMATIC ICE CUBE MAKER: Refrigerating

mechanism designed to produce ice cubes inquantity automatically.

AUTO TRANSFORMER: A transformer in whichboth primary and secondary coils have turns in

common. Step-up or step-down of voltage isaccomplished by taps on common winding.

AZEOTROPIC MIXTURE: Example of aze-otropic

mixture--refrigerant R-502 is mixture consisting of48.8% refrigerant R-22, and 51.2% R-115. The

refrigerants do not combine chemically, yetazeotropic mixture provides refrigerant character-

istics desired.

BACK PRESSURE: Pressure in low side of

refrigerating system; also called suction pressure or

low side pressure.

BAFFLE: Plate or vane used to director-control

movement of fluid or air within confined area.

BALL CHECK VALVE:Valve assembly (ball) which

permits flow of fluid in one direction only.

BALLOON TYPE GASKET: Flexible refrigeratordoor gasket having a large cross section.

BAROMETER: Instrument for measuring

atmospheric pressure. It may be calibrated inpounds per square inch or in inches of mercury incolumn.

BATH: A liquid solution used for cleaning, plating,

or maintaining a specified temperature.

BATTERY; Electricity producing cells which use

interaction of metals and chemicals to create

electrical current flow.

BAUDELOT COOLER: Heat exchanger in whichwater flows by gravity over the outside of the tubesor plates.

BEARING: Low friction device for supporting andaligning a moving part,

BELLOWS: Corrugated cylindrical containerwhich moves as pressures change, or provides a

seal during movement of parts.

BENDING SPRING: Coil spring which is mountedon inside or outside to keep tube from collapsing

while bending it.

BERNOULLI'S THEOREM: In stream of liquid,sum of elevation head, pressure head and velocityremains constant along any line of flow provided no

work is done by or upon liquid in course of its flow,

and decreases in proportion to energy lost in flow.

BIMETAL STRIP: Temperature regulating orindicating device which works on principle that twodissimilar metals with unequal expansion rates,

welded together, will bend as temperatures change.

BLEED-VALVE: Vaive with small opening-insidewhich permits a minimum fluid flow when valve isclosed.

BOILER: Closed container in which a liquid maybe heated and vaporized.

BOILING TEMPERATURE: Temperature atwhich a fluid changes from a liquid to a gas.

BORE: Inside diameter of a cylindrical hole.

BOURDON TUBE:As used in pressure gauges.

Thin walled tube of elastic metal flattened and bentinto circular shape, which tends to straighten as

pressure inside is increased.


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BOWDEN CABLE:Tube containing a wire used toregulate a valve or control from a remote point.

BOYLE'S LAW:Law of physicsvolume of a gasvaries as pressure varies, if temperature remains

the same. Examples: If pressure is doubled onquantity of gas, volume becomes one half. If vol-

ume becomes doubled, gas has its pressurereduced by one half.

BRAZING: Method of joining metals withnonferrous filler (without iron) using heat between

800 deg. F. and melting point of base metals.

BREAKER STRIP:Strip of wood or plastic used tocover joint between outside case and inside liner of

refrigerator.

BRINE: Water saturated with chemical such assalt.

BRITISH THERMAL UNIT (BTU): Quantity of

heat required to raise temperature of one pound ofwater one degree F.

BULB, SENSITIVE: Part of sealed fluid device

which reacts to temperature to be measured, orwhich will control a mechanism.

BUNKER: In commercial installations/ space in

which ice or cooling element is installed.

BURNER: Device in which combustion of fuel

takes place.

BUTANE: Liquid hydrocarbon (C4H20) commonlyused as fuel for heating purposes.

BYPASS: Passage at one side of, or aroundregular passage.

CADMIUM PLATED: Parts coated with thin

corrosion-resistant covering of cadmium metal.

CALCIUM SULFATE: Chemical compound

(CaSO.4) which is used as a drying agent ordesiccant in liquid line driers.

CALIBRATE: To determine; position indicatorsas required to obtain accurate measurements.

CALORIE: Heat required to raise temperature of

one gram of water one degree centigrade.

CALORIMETER: Device used to measure

quantities of heat or determine specific heats.

CAPACITANCE (C): Property of nonconductor(condenser or capacitor) that permits storage of

electrical energy in an electrostatic field.

CAPACITOR: Type of electrical storage device

used in starting and/or running circuits on manyelectric motors.

CAPACITOR-START MOTOR: Motorwhich has a

capacitor in the starting circuit.

CAPILLARY TUBE: A type of refrigerant control.

Usually consists of several feet of tubing havingsmall inside diameter. Friction of liquid refrigerant

and bubbles of vaporized refrigerant within tube

serve to restrict flow so that correct high side and

low side pressures are maintained while thecompressor is operating. A capillary tube refrigerant

control allows high side and low side pressures tobalance during off cycle. Also; small diameter

tubing used to connect temperature control bulbs tocontrol mechanisms.

CARBON DIOXIDE (C02): Compound of carbonand oxygen which is sometimes used as a

refrigerant. Refrigerant number is R-744.

CARBON FILTER: Air filters using activatedcarbon as air cleansing agent.

CARBON TETRACHLORIDE: A colorless

nonflammable liquid used as solvent and in fireextinguishers. Very toxic. Should never be allowedto touch skin/ or fumes inhaled.

CARRENE:A refrigerant in group 1 (R-ll). Chemicalcombination of carbon, chlorine and fluorine.

CASCADE SYSTEMS:Arrangement inwhich two ormore refrigerating systems are used in series; usescooling coil of one machine to cool condenser of

other machine. Produces ultra-low temperatures.

CASEHARDENED: Heat treating ferrous metals(iron) so surface layer is harder than interior.

CATHODE: Negative terminal of an electricaldevice. Electrons leave the device at this terminal.

CELSIUS: German language word for centigrade,

the metric system temperature scale

CENTIGRADE SCALE:Temperature scale used in

metric system. Freezing point of water is 0; boilingpoint 100.

CENTIMETER: Metric unit of linear measurementwhich equals .3937 inches.

CENTRIFUGAL COMPRESSOR: Compressor

which compresses gaseous refrigerants by

centrifugal force.CHARGING BOARD: Specially designed panel or

cabinet fitted with gauges, valves and refrigerantcylinders used for charging refrigerant and oil into

refrigerating mechanisms.

CHARLES' LAW:The volume of a given mass of

gas at a constant pressure varies according to ftstemperature.

CHECK VALVE:A device which permits fluid flow


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only in one direction.

CHEMICAL REFRIGERATION: A system of

cooling using a disposable refrigerant.

CHIMNEY EFFECT:Tendency of air or gas to rise

when heated.

CHOKE TUBE:Throttling device used to maintaincorrect pressure difference between high side and

low side in refrigerating mechanism. Capillary tubesare sometimes called choke tubes.

CIRCUIT: A tubing, piping or electrical wireinstallation which permits flow from the energy

source back to energy source.

CIRCUIT BREAKERS: Safety device whichautomatically opens an electrical circuit if

overloaded.

CIRCUIT, PARALLEL: Arrangement ofelectrical devices in which all positive terminals are

joined to one conductor and all negative terminalsto other conductor.

CIRCUIT, SERIES:Electrical wiring: electrical path(circuit) in which electricity to operate second lampor device must pass through first, and so on;

current flow travels through all devices connected

together.

CLEARANCE POCKET COMPRESSOR: A small

space in cylinder from which compressed gas is notcompletely expelled. This space is called the

compressor clearance space or pocket. For effectiveoperation, compressors are designed to have as

small clearance space as possible.

CLOSED CIRCUIT:An electrical circuit in which

electrons are flowing.

CLUTCH, ARMATURE: The part of theautomotive compressor magnetic clutch which is

attracted by the magnetic field and causes thecompressor to be turned by a belt drive when the

magnetic field is energized.

CLUTCH, FIELD:The coils of wire through which

the current flows to create the magnetic forcewhich engages the magnetic clutch.

CLUTCH, MAGNETIC:Clutch built into automobilecompressor flywheel, operated magnetically, whichallows pulley to revolve without driving compressor

when refrigerating effect is not required.

CODE INSTALLATION: A refrigeration or airconditioning installation which conforms to the localcode and/or the national code for safe and efficient

installations.

COEFFICIENT OF CONDUCTIVITY: The measureof the relative rate at which different materials

conduct heat. Copper is a good conductor of heatand therefore, has a high coefficient of conductivity.

COEFFICIENT OF PERFORMANCE (COP): Theratio of work or energy applied as compared to the

energy used.

C02 INDICATOR: An instrument used to

indicate, the percent of carbon dioxide in stack

gases.

COLD: Cold is the absence of heat; a temperature

considerably below normal.

COLD JUNCTION: That part of a thermoelectric

system which absorbs heat as the system operates,

COLD WALL: Refrigerator construction which

has the inner lining of refrigerator serving as the

cooling surface.

COLLOIDS: Miniature cells in meat, fish andpoultry.

COMFORT CHART:Chart used in air conditioningto show the dry bulb temperature and humidity for

human comfort conditions.

COMFORT COOLER:A system used tore-duce the

temperature in the living space in homes. Thesesystems are not complete air conditioners as they

do not provide complete control of heating, humid-ifying, dehumidification, and air circulation.

COMFORT ZONE: Area on psychrometric chart

which shows conditions of temperature, humidity,and sometimes air movement, in which most people

are comfortable.COMMUTATOR: Part of electric motor rotor

which conveys electric current to rotor 'windings.

COMPOUND GAUGE: Instrument for measuringpressures both above and below atmospheric

pressure,

COMPOUND REFRIGERATING SYSTEMS:

System which has several compressors orcompressor cylinders in series. The system is used

to pump low pressure vapors to condensingpressures.

COMPRESSION: Term used to denote increase

of pressure on a fluid by using mechanical energy.

COMPRESSION GAUGE: Instrument used to

measure positive pressures (pressures aboveatmospheric pressures) only. These gauges are

usually calibrated from 0 to 300 pounds per squareinch of pressure, Gauge, (psig).

COMPRESSOR: The pump of a refrigeratingmechanism which draws a vacuum or low pressure

on cooling side of refrigerant cycle and squeezes or


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compresses the gas into the high pressure orcondensing side of the cycle.

COMPRESSOR, HERMETIC: Compressor inwhich driving motor is sealed in the same dome or

housing that contains the compressor,

COMPRESSOR, OPEN-TYPE: Compressor inwhich the crankshaft extends through the crankcase

and is driven by an outside motor.

COMPRESSOR, RECIPROCATING: Compressor

which uses a piston and cylinder mechanism toprovide pumping action.

COMPRESSOR, ROTARY: A compressor whichuses vanes, eccentric mechanisms, or other rotating

devices to provide pumping action.

COMPRESSOR SEAL: Leak proof seat betweencrankshaft and compressor body.

CONDENSATE: Fluid which forms on an

evaporator.

CONDENSATE PUMP: Device used to remove

fluid condensate that collects beneath anevaporator.

CONDENSATION: Liquid or droplets which formwhen a gas or vapor is cooled below its dew point.

CONDENSE: Action of changing a gas or vapor

to a liquid.

CONDENSER:The part of refrigeration mechanism

which receives hot, high pressure refrigerant gasfrom compressor and cools gaseous refrigerant until

it returns to liquid state.

CONDENSER, AIR-COOLED:A heat exchanger

which transfers heat to surrounding air.

CONDENSER COMB: Comb-like device, metal orplastic, which is used to straighten the metal fins on

condensers or evaporators.

CONDENSER FAN: Forced air device used tomove air through air-cooled condenser.

CONDENSER, WATER-COOLED: Heat ex-changer which is designed to transfer heat from hot

gaseous refrigerant to water.

CONDENSER WATER PUMP: Forced water

moving device used to move water through

condenser.

CONDENSING UNIT: That part of refrigerating

mechanism which pumps vaporized refrigerant fromevaporator, compresses it, liquefies it in the

condenser and returns the liquid refrigerant to re-frigerant control.

CONDENSING UNIT SERVICE VALVES: Shutoff

hand valves mounted on condensing unit to enableserviceman to install anqVor service unit.

CONDUCTIVITY: Ability of a metal or asubstance to conduct or transmit heat ana/or

electricity.

CONDUCTOR: Substance or body capable oftransmitting electricity, heat, etc.

CONNECTING ROD: That part of compressormechanism which connects piston to crankshaft.

CONSTRICTOR: Tube or orifice used to restrictflow of a gas or a liquid.

CONTAMINANT: A substance (dirt, moisture, or

other substance) foreign to refrigerant orrefrigerant oil in system.

CONTINUOUS CYCLE ABSORPTION SYSTEM:

System which has a continuous flow of energyinput.

CONTROL: Automatic or manual device used to.stop, start and/or regulate flow of gas, liquid,

ana/or electricity.

CONTROL, COMPRESSOR:See Motor Control.

CONTROL, DEFROSTING:Device to automaticallydefrost evaporator. It may operate by means of a

clock, door cycling mechanism, or during "off"

portion of refrigerating cycle,

CONTROL, LOW PRESSURE: Cycling device

connected to low pressure side of system,

CONTROL, MOTOR: A temperature or pressureoperated device used to control running of motor.

CONTROL, PRESSURE MOTOR: A high or lowpressure control which is connected into the

electrical circuit and used to start and stop motor

when there is need for refrigeration or for safetypurposes.

CONTROL, REFRIGERANT: Device used toregulate flow of liquid refrigerant into evaporator;

such as capillary tube, expansion valves, high andlow side float valves, etc.

CONTROL, TEMPERATURE: A thermo-static

device which automatically stops and starts motor,operation of which is based on temperaturechanges.

CONTROLLED EVAPORATOR PRESSURE:Controlled system which maintains definite pressure

or range of pressures in evaporator,

CONVECTION: Transfer of heat by means ofmovement or flow of a fluid or gas.

CONVECTION, FORCED: Transfer of heat


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resulting from forced movement of liquid or gas bymeans of fan or pump.

CONVECTION, NATURAL: Circulation of a gas orliquid due to difference in density resulting from

temperature differences.

CONVERSION FACTORS: Force and power maybe expressed in more than one way. A horsepower

is equivalent to 33,000 foot pounds of work perminute, 746 watts, or 2,546 Btu per hour. Thesevalues can be used for changing horsepower into

foot pounds, Btu or watts.

COOLING TOWER: Device which cools water bywater evaporation in air. Water is cooled to wet

bulb temperature of air.

COPPER PLATING:Condition developing in someunits in which copper is electrolytic ally deposited

on compressor part surfaces.

CORE, MAGNETIC: Magnetic center of a magneticfield.

COULOMB: Quantity of electricity transferred by

electric current of one ampere in one second.

COUNTER EMF:Tendency for reverse electrical

flow as magnetic field changes in an induction coil.

COUNTERFLOW: Flow in opposite direction.

"CRACKING" A VALVE: Opening valve a smallamount.

CRANKSHAFT SEAL: Leak proof joint betweencrankshaft and compressor body.

CRANK THROW: Distance between center line ofmain bearing journal and center line of the crankpin

or eccentric,

CRISPER: Drawer or compartment in refrigeratordesigned to provide high humidity along with low

temperature to keep vegetables, especially leafyvegetables, cold and crisp,

CRITICAL PRESSURE: Condition of refrigerantat which liquid and gas have same properties.

CRITICAL TEMPERATURE: Temperature at

which vapor and liquid have same properties.

CRITICAL VIBRATION: Vibration which is

noticeable and harmful to structure.

CROSS CHARGED: Sealed container containingtwo fluids which together create a desired pressure-

temperature curve.

CRYOGENIC FLUID:Substance which exists as a

liquid or gas at ultra-low temperatures (-250 F. orlower).

CRYOGENICS: Refrigeration which deals with

producing temperatures of 250 F. below zero andlower.

CURRENT (1): Transfer of electrical energy inconductor by means of electrons changing position.

CURRENT RELAY: Device which opens or closes a

circuit based on change of current flow.

CUT-IN: Temperature or pressure valve which

closes control circuit.

CUT-OUT: Temperature or pressure valve whichopens control circuit.

CYCLE: Series of events which have tendency torepeat same events in same order.

CYLINDER HEAD: Part which enclosescompression end of compressor cylinder,

CYLINDER, REFRIGERANT: Cylinder in which

refrigerant is purchased and dispensed. Color code

pointed on cylinder indicates kind of refrigerantcylinder contains.

CYLINDRICAL COMMUTATOR:Commutator with

contact surfaces parallel to the rotor shaft.

DALTON'S LAW: Vapor pressure exerted oncontainer by a mixture of gases is equal to sum ofindividual vapor pressures of gases contained in

mixture.

DAMPER: Valve for controlling airflow.

DECIBEL: Unit used for measuring relativeloudness of sounds. One decibel is equal to

approximate difference of loud-ness ordinarilydetectable by human ear, the range of which is

about 130decibals on scale beginning with one forfaintest audible sound.

DEFROST CYCLE: Refrigerating cycle in which

evaporator frost and ice accumulation is melted.

DEFROST TIMER: Device connected into

electrical circuit which shuts unit off long enough topermit ice and frost accumulation on evaporator to

melt.

DEFROSTING: Process of removing frost

accumulation from evaporators.

DEFROSTING TYPE EVAPORATOR: An

evaporator operating at such temperatures that ice

and frost on surface melts during off part ofoperating cycle.

DECREASING: Solution or' solvent used toremove oil or grease from refrigerator parts.

DEGREE-DAY: Unit that represents one degreeof difference from given point in average outdoor

temperature of one day and is often used in


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estimating fuel requirements for a building. Degree-days are based on average temperature over a 24hour period. As an example; if an average

temperature for a day is 50 F., the number ofdegree-days for that day would be equal to 65 F.

minus 50 F. or 15 degree-days (65-50= 15).

Degree-days are useful when calculating require-ments for heating purposes.

DEHUMIDIFIER: Device used to removemoisture from air in enclosed space.

DEHYDRATED OIL: Lubricant which has hadmost of water content removed dry oil).

DEHYDRATOR: (See Drier.)

DEHYDRATOR-RECEIVER: A small tank which

serves as liquid refrigerant reservoir and which alsocontains a desiccant to remove moisture. Used on

most automobile air conditioning installations.

DEICE CONTROL: Device used to operaterefrigerating system in such a way as to providemeltina of the accumulated ice and frost.

DELTA TRANSFORMER:A three-phase electricaltransformer which has ends of each of three

windings electrically connected.

DEMAND METER:An instrument used to measure

kilowatt-hour consumption of a particular circuit orgroup of circuits,

DENSITY: Closeness of texture or consistency.

DEODORIZER: Device which absorbs various

odors, usually by principle of absorption. Activated

charcoal is a common substance used.

DESICCANT: Substance used to collect and

hold moisture in refrigerating system. A dryingagent. Common desiccants are activated alumina,

silica gel.

DETECTOR, LEAK: Device used to detect and

locate refrigerant leaks.

DEW POINT: Temperature at which vapor (at 100percent humidity) begins to condense and deposit

as liquid.

DIALECTRIC FLUID: Fluid with high electricalresistance.

DIAPHRAGM: Flexible membrane usually madeof thin metal, rubber, or plastic.

DICHLORODIFLUROMETHANE: Refrigerantcommonly known as R-12. Chemical formula is

CCI2F2- Cylinder color code is white. Boiling pointat atmospheric pressure is -21.62 F.

DIE CAST: A process of moulding low melting

temperature metals in accurately shaped metal moulds.

DIE STOCK: Tool used to hold dies with external

threads.

DIES (THREAD): Tool used to cut external threads.DIFFERENTIAL: As applied to refrigeration and

heating: difference between "cut-in" and "cut-out"temperature and pressure of a control.

DIODE: A two-element electron tube which will allowmore electron flow in one direction in a circuit than in

the other direction; tube which serves a rectifier.

DIRECT CURRENT: Electron flow which movescontinuously in one direction in circuit.

DIRECT EXPANSION EVAPORATOR: An

evaporator coil using either an automatic expansionvalve (AEV) or a thermostatic expansion valve (TEV)

refrigerant control.

DISPLACEMENT, PISTON: Volume obtained by

multiplying area of cylinder bore by length of pistonstroke.

DISTILLING APPARATUS: Fluid reclaiming device

used to reclaim used refrigerants. Reclaiming is usuallydone by vaporizing and then recondensing refrigerant.

DOME-HAT.; Sealed metal container for the motor-compressor of a refrigerating unit.

DOUBLE DUTY CASE: Commercial refrigerator

which has part of it for refrigerated storage and partequipped with glass windows for display purposes.

DOUBLE THICKNESSFLARE: Copper, aluminum or

steel tubing end which has been formed into two-wall

thickness, 37 to 45 deg. bell mouth or flare.

DOWEL PIN: Accurately dimensioned pin pressedinto one assembly part and slipped into another

assembly part to insure accurate alignment.

DRAFT GAUGE: Instrument used to measure air

movement.

DRAFT INDICATOR:An instrument used to indicate

or measure chimney draft or combustion gas

movement. Draft is measured in units of .1 inch ofwater column.

DRIER: A substance or device used to remove

moisture from a refrigeration system.DRIP PAN: Pan-shaped panel or trough used tocollect condensate from evaporator coil.

DRY BULB: An instrument with sensitive elementwhich measures ambient (moving) air temperature.

DRY BULB TEMPERATURE: Air temperature asindicated by ordinary thermometer.

DRY CAPACITOR CONDENSER: An electrical devicemade of dry metal and dry insulation, used to store


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electrons.

DRY CELL BATTERY: Electrical device used to provide

DC electricity, having no liquids in the cells.

DRY ICE: A refrigerating substance made of solid

carbon dioxide which changes directly from a solid to a

gas (sublimates). Its subliming temperature is 109 F.

below zero.

DRY SYSTEM:A refrigeration system which has theevaporator liquid refrigerant mainly in the atomized or

droplet condition.

DUCT: Heating and air conditioning. A tube or

channel through which air is conveyed or moved.

DYNAMOMETER: Device for measuring power

output or power input of a mechanism.

EBULATOR: A pointed or sharp edged solid

substance inserted in flooded type evaporators to

improve evaporation (boiling) of refrigerant in coil.

ECCENTRIC: A circle or disk mounted off center.

Eccentrics are used to adjust controls and connectcompressor drive-shafts to pistons.

EFFECTIVE AREA:Actual flow area of an atr inlet oroutlet. Gross area minus area of vanes or grille bars.

EFFECTIVE TEMPERATURE: Overall effect on ahuman of air temperature, humidity and air movement.

EJECTOR: Device which uses high fluid velocity such

as a venturi, to create low pressure or vacuum at itsthroat to draw in fluid from another source.

ELECTRIC DEFROSTING: Use of electric resistance

heating coils to melt ice and frost off evaporatorsduring defrosting.

ELECTRIC HEATING:House heating system in whichheat from electrical resistance units is used to heat

rooms.

ELECTRIC WATER VALVE: Solenoid type

(electrically operated) valve used to turn water flow on

and off.

ELECTROLUX SYSTEM: Trade name for a

continuously operating absorption type of refrigeratingsystem.

ELECTROLYTIC CONDENSER-CAPACITOR: Plateor surface capable of storing small electrical charges.

Common electrolytic condensers are formed by rolling

thin sheets of foil between insulating materials.Condenser capacity is expressed in microfarads.

ELECTROMAGNET: Made by winding coil of wirearound soft iron core. When electric current is run

through wire, coil becomes a magnet.

ELECTROMOTIVE FORCE (EMF) VOLTAGE:

Electrical force which causes current (free electrons) toflow or move in an electrical circuit. Unit of measure-

ment is the volt.

ELECTRON: Elementary particle or portion of anatom which carries a negative charge.

ELECTRONICS: Field of science dealing withelectron devices and their uses.

ELECTRONIC LEAK DETECTOR: Electronicinstrument which measures electronic flow across gas

gap. Electronic flow changes indicate presence of re-frigerant gas molecules.

ELECTRONIC SOUND TRACER: Instrument

used to detect leaks by locating source of high

frequency sound caused by leak.

ELECTROSTATIC FILTER:Type of filter which givesparticles of dust electric charge. This causes particles

to be attracted to plate so they can be removed fromair strearn or atmosphere.

END BELL: End structure of electric motor which

usually holds motor bearings.

END PLAY: Slight movement of shaft along center

line.

ENTHALPY: Total amount of heat in one pound of a

substance calculated from accepted temperature base.Temperature of 32 deg. F. is accepted base for water

vapor calculation. For refrigerator calculations,

accepted base is -40 deg, F.

ENTROPY: Mathematical factor used in engineering

calculations. Energy in a system,

ENZYME: A complex organic substance originating

from living cells that speeds up chemical changes infoods. Enzyme action is slowed by cooling.

EPOXY (RESINS):A synthetic plastic adhesive.

EQUALIZER TUBE: Device used to maintain equal

pressure or equal liquid levels between two containers.

EVAPORATION: A term applied to the changing of

a liquid to a gas. Heat is absorbed in this process.

EVAPORATIVE CONDENSER:A device which uses

open spray or spill water to cool a condenser.Evaporation of some of the water cools the condenser

water and reduces water consumption.

EVAPORATOR: Part of a refrigerating mechanism inwhich the refrigerant vaporizes and absorbs heat,

EVAPORATOR COIL: Device made of a coil oftubing which functions as a refrigerant evaporator.

EVAPORATOR, DRY TYPE:An evaporator into whichrefrigerant is fed from a pressure reducing device. Little

or no liquid refrigerant collects in the evaporator


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HVAC STEPS SAFE

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EVAPORATOR FAN: Fan which cools ex-tended heat

exchange surface of evaporator.

EVAPORATOR, FLOODED:An evaporator containingliquid refrigerant at all times.

EXPANSION VALVE':A device in refrigerating system

which maintains a pressure difference between the

high side and low side and is operated by pressure.

EXPENDABLE REFRIGERANT SYSTEM: Systemwhich discards the refrigerant after it has evaporated.

EXTERNAL EQUALIZER: Tube connected to lowpressure side of an expansion valve diaphragm and to

exit of evaporator.

FAHRENHEIT SCALE: On a Fahrenheit

thermometer, under standard atmospheric pressure,

boiling point of water is 212 deg. and freezing point is32 deg. above zero on its scale.

FAIL SAFE CONTROL: Device which opens circuit

when sensing element fails to operate.FAN: A radial or axial flow device used for moving orproducing artificial currents of air.

FARAD: Unit of electrical capacity; capacity of a

condenser which, when charged with one coulomb ofelectricity, gives difference of potential of one volt.

FARADAY EXPERIMENT: Silver chloride absorbs

ammonia when cool and releases ammonia whenheated. This is basis on which some absorption

refrigerators operate.

FIELD POLE: Part of stator of motor which

concentrates magnetic field of field winding,

FILE CARD: Tool used to clean metal files.

FILTER: Device for removing small particles from a

fluid.

FLA: Full load amperes.

FLAME TEST FOR LEAKS: Tool which is principally a

torch and when an air-refrigerant mixture is fed toflame, this flame will change color in presence of

heated copper.

FLAPPER VALVE: The type of valve used in

refrigeration compressors which allows gaseous

refrigerants to flow in only one direction.FLARE: Copper tubing is often connected to parts of

refrigerating system by use of flared fittings. Thesefittings require that the end of tube be expanded at

about 45 deg. angle. This flare is firmly gripped byfittings to make a strong leakproof seal.

FLARE NUT:Fitting used to clamp tubing flare againstanother fitting.

FLARED SINGLE THICKNESS CONNECTION:Tube ending formed into 37 1/2 deg. or 45 deg. bell

mouth or flare.

FLASH GAS:This is the instantaneous evaporation

of some liquid refrigerant in evaporator which coolsremaining liquid refrigerant to desired evaporation tem-

perature.

FLASH POINT: Temperature at which oil will give off

sufficient vapor to support a flash flame but will notsupport continuous combustion.

FLASH WELD:A resistance type weld in which mating

parts are brought together under considerable pressureand a heavy electrical current is passed through the

joint to be welded.

FLOAT VALVE: Type of valve operated by sphere or

pan which floats on liquid surface and controls level of

liquid.

FLOODED SYSTEM:Type of refrigerating system in

which liquid refrigerant fills evaporator.

FLOODED SYSTEM, LOW SIDE FLOAT:Refrigerating system which has a low side floatrefrigerant control.

FLOODING: Act of filling a space with a liquid.

FLOW METER: Instrument used to measure velocityor volume of fluid movement.

FLUE: Gas or air passage which usually depends on

natural convection to cause the combustion gases toflow through it. Forced convection may sometimes be

used.

FLUID: Substance in a liquid or gaseous state;

substance containing particles which move and changeposition without separation of the mass.

FLUID COUPLING: Device which transmits drive

energy to energy absorber through a fluid.

FLUSH: An operation to remove any material or fluids

from refrigeration system parts by purging them to theatmosphere using refrigerant or other fluids.

FLUX- BRAZING, SOLDERING: Substance applied tosurfaces to be joined by brazing or soldering to free

them from oxides and facilitate good joint.

FLUX, MAGNETIC: Lines of force of a magnet.

FOAM LEAK DETECTOR:A system of soap bubbles orspecial foaming liquids brushed over joints andconnections to locate leaks.

FOAMING: Formation of a foam in an oil-refrigerant

mixture due to rapid evaporation of refrigerantdissolved in the oil. This is most likely to occur whenthe compressor starts and the pressure is suddenly

reduced.

FOOT POUND:A unit of work. A foot pound is theamount of work done in lifting one pound one foot.


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HVAC STEPS SAFE

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FORCE: Force is accumulated pressure and is

expressed in pounds. If the pressure is 10 psi on aplate of 10 sq. in. area, the force is 100 pounds.

FORCED CONVECTION: Movement of fluid by

mechanical force such as fans or pumps.

FORCE-FEED OILING: A lubrication system which

uses a pump to force oil to surfaces of moving parts.

FREEZER ALARM: Device used in many freezerswhich sounds an alarm (bell or buzzer) when freezer

temperature rises above safe limit.

FREEZER BURN:A condition applied to food which

has not been properly wrapped and that has becomehard, dry, and discolored.

FREEZE-UP: 1-The formation of ice in the

refrigerant control device which may stop the flow ofrefrigerant into the evaporator. 2-Frost formation on a

coil may stop the airflow through the coil.

FREEZING: Change of state from liquid to solid.FREEZING POINT: The temperature at which aliquid will solidify upon removal of heat. The freezing

temperature for water is 32 F. at atmospheric pressure.

FREON: Trade name for a family of syntheticchemical refrigerants manufactured by DuPont De

Nemours Inc.

FROST BACK: Condition in which liquid refrigerantflows from evaporator into suction line; indicated by

frost formation on suction line.

FROST CONTROL, AUTOMATIC: A control which

automatically cycles refrigerating system based on frostformation on evaporator.

FROST CONTROL, MANUAL:A manual control used

to change refrigerating system to produce defrostingconditions.

FROST CONTROL, SEMIAUTOMATIC: A controlwhich starts defrost part of a cycle manually and then

returns system to normal operation automatically.

FROST FREE REFRIGERATOR: A refrigerated

cabinet which operates with an automatic defrostduring each cycle.

FROSTING TYPE EVAPORATOR: A refrigerating

system which maintains the evaporator at frostingtemperatures during all phases of cycle.

FULL FLOATING:A mechanism construction in whicha shaft is free to turn in all the parts in which it is

inserted.

FUSE: Electrical safety device consisting of strip offusible metal in circuit which melts when current isoverloaded.

FUSIBLE PLUG:A plug or fitting made with a metal

of a known low melting temperature, used as

safety device to release pressures in case of fire.

GALVANIC ACTION: Corrosion action between two

metals of different electronic activity. The action isincreased in the presence of moisture.

GAS: Vapor phase or state of a substance.

GASKET: A resilient or flexible material used betweenmating surfaces of refrigerating unit parts or of

refrigerator doors to provide a leakproof seal.

GASKET, FOAM: A joint sealing device made ofrubber or plastic foam strips.

GAS - NONCONDENSIBLE: A gas which will notform into a liquid under pressure-temperature

conditions.

GAS VALVE: Device for controlling flow of gas.

GAUGE, COMPOUND: Instrument for measuring

pressures both below and above atmospheric pressure.

GAUGE, HIGH PRESSURE:Instrument for measuringpressures in range of 0 psig to 500 psig.

GAUGE, LOW PRESSURE: Instrument for measuringpressures in range of 0 psig and 50 psig.

GAUGE MANIFOLD: A device constructed to holdcompound and high pressure gauges and valved to

control flow of fluids through it.

GAUGE, VACUUM: Instrument used to measurepressures below atmospheric pressure.

GRAIN: A unit of weight and equal to one 7000th ofa pound. It is used to indicate the amount of moisture

in the air.

GRILLE: An ornamental or louvered opening placed at

the end of an air passageway.

GROMMET: A plastic metal or rubber doughnut-

shaped protector for wires or tubing as they pass

through hole in object,

GROUND COIL: A heat exchanger buried in the

ground which may be used either as an evaporator oras a condenser.

GROUND, SHORT CIRCUIT:A fault in an electricalcircuit allowing electricity to flow into the metal parts of

the structure.

GROUND WIRE: An electrical wire which will safelyconduct electricity from a structure into the ground.

HALIDE REFRIGERANTS: Family of refrigerants

containing halogen chemicals.

HALIDE TORCH: Type of torch used to detect

halogen refrigerant leaks.

HASTELLOY: Trade name for a hard-on-corroding

metal alloy.

HEAD PRESSURE: Pressure which exists in


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HVAC STEPS SAFE

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condensing side of refrigerating system.

HEAD PRESSURE CONTROL: Pressure operated

control which opens electrical circuit if high sidepressure becomes excessive.

HEAD, STATIC:Pressure of fluid expressed in terms

of height of column of the fluid, such as water or

mercury.

HEAD, VELOCITY: In flowing fluid, height of fluidequivalent to its velocity pressure.

HEAT: Form of energy the addition of which causessubstances to rise in temperature; energy associated

with random motion of molecules.

HEAT EXCHANGER: Device used to transfer heat

from a warm or hot surface to a cold or cooler surface.

Evaporators and condensers are heat exchangers.

HEAT LAG: When "a substance is heated on one

side, it takes time for the heat to travel through the

substance. This time is called heat lag.HEAT LEAKAGE: Flow of heat through a substance iscalled heat leakage.

HEAT LOAD: Amount of heat; measured in Btu,

which is removed during a period of 24 hours.

HEAT OF COMPRESSION: Mechanical energy of

pressure transformed into energy of heat.

HEAT OF FUSION: The heat released in changinga substance from a liquid state to a solid state. The

heat of fusion of ice is 144 Btu per pound.

HEAT OF RESPIRATION: The process by which

oxygen and carbohydrates are assimilated by asubstance; also when carbon dioxide and water are

given off by a substance.

HEAT PUMP: A compression cycle system used tosupply heat to a temperature controlled space, which

can also remove heat from the same space.

HEAT TRANSFER:Movement of heat from one body

or substance to another. Heat may be transferred byradiation, conduction, convection or a combination of

these three methods.

HEATING COIL: A heat transfer device whichreleases heat.

HEATING CONTROL: Device which controls

temperature of heat transfer unit which releases heat.

HEATING VALUE: Amount of heat which may be

obtained by burning a fuel. It is usually expressed inBtu per pound or Btu per gallon.

HEAVY ENDS, HYDROCARBON OILS: The heavymolecules or larger molecules of hydrocarbon oils.

HERMETIC MOTOR: Compressor drive motor sealedwithin same casing which contains compressor.

HERMETIC SYSTEM: Refrigeration system whichhas a compressor driven by a motor contained incompressor dome or housing.

HG - (MERCURY): Heavy silver-white metallic

element; only metal that is liquid at ordinary room

temperature. Symbol, Hg.

HIGH PRESSURE CUT-OUT: Electrical controlswitch operated by the high side pressure whichautomatically opens electrical circuit if too high head

pressure or condensing pressure is reached.

HIGH SIDE: Parts of a refrigerating system which

are under condensing or high side pressure.

HIGH SIDE FLOAT; Refrigerant control mechanism

which controls the level of the liquid refrigerant in the

high pressure side of mechanism.

HIGH VACUUM PUMP: Mechanism which can create

vacuum in 1000 to 1 micron range.

HI-RE-LI SYSTEM: A patented heat pump cycledeveloped by Westinghouse Corp,

HOLLOW TUBE GASKET: Sealing device made ofrubber or plastic with tubular cross section.

HONE: Fine-grit stone used for precision sharpening.

HORSEPOWER: A unit of power equal to 33,000

foot pounds of work per minute. One electrical

horsepower equals 746 watts.

HOT GAS BYPASS: Piping system in refrigerating unit,

which moves hot refrigerant gas from condenser intolow pressure side.

HOT GAS DEFROST: A defrosting system in whichhot refrigerant gas from the high side is directed

through evaporator for short period of time and at

predetermined intervals in order to remove frost fromevaporator.

HOT JUNCTION: That part of thermoelectric circuitwhich releases heat.

HOT WIRE: A resistance wire in an electrical relaywhich expands when heated and contracts when

cooled.

HUMIDIFIERS:-Device used to add to and control the

humidity in a confined space.

HUMIDISTAT: An electrical control which isoperated by changing humidity.

HUMIDITY: Moisture; dampness. Relative humidity

is ratio of quantity of vapor present in air to greatest,amount possible at given temperature.

HYDROLEN - TAR: A hydrocarbon byproduct of oilindustry. Used as a low melting temperature,

waterproof sealing compound.

HYDROMETER: Floating instrument used to


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HVAC STEPS SAFE

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measure specific gravity of a liquid. Specific gravity is

ratio of weight of any volume of a substance to weightof equal volume of substance used as a standard.

HYDRONIC: Type of heating system which

circulates a heated fluid, usually water, throughbaseboard coils. Circulating pump is usually controlled

by a thermostat.

HYGROMETER: An instrument used to measuredegree of moisture in the atmosphere.

HYGROSCOPIC: Ability of a substance to absorb andretain moisture and change physical dimensions as its

moisture content changes.

ICC - INTERSTATE COMMERCE COMMISSION: A

government body which controls the design and

construction of pressure containers.

ICE CREAM CABINET: Commercial refrigerator

which operates at approximately 0 F. and is used forstorage of ice cream.

ICE MELTING EQUIVALENT (I.M.E.) (ICEMELTING EFFECT): Amount of heat absorbed by

melting ice at 32 F. is 144 Btu per pound of ice or288,000 Btu per ton.

IDLER: A pulley used on some belt drives to provide

the proper belt tension and to eliminate belt vibration.

IGNITION TRANSFORMER: A transformer designed

to provide a high voltage current. Used in manyheating systems to ignite fuel.

IMPELLER: Rotating part of a centrifugal pump.

INDUCED MAGNETISM:Ability of a magnetic field toproduce magnetism in a metal.

INDUCTION MOTOR: An AC motor which operates

on principle of rotating magnetic field. Rotor has noelectrical connection, but receives electrical energy by

transformer action from field windings.

INFRARED LAMP: An electrical device which emits

infrared rays; invisible rays just beyond red in thevisible spectrum.

INSULATION, THERMAL: Substance used to retardor slow flow of heat through wall or partition.

INTERMITTENT CYCLE:A cycle which repeats itself

at different intervals.

IR DROP:An electrical term indicating the loss in acircuit expressed in amperes x resistance (I x R) orvoltage drop.

ISOTHERMAL: Changes of volume or pressure under

conditions of constant temperature.

ISOTHERMAL EXPANSION AND CON-

TRACTION: An action which takes place without atemperature change.

JOULE-THOMSON EFFECT: Change in temperatureof a gas on expansion through a porous plug from ahigh pressure to a lower pressure.

JOURNAL, CRANKSHAFT: Part of shaft which

contacts the bearing.

JUNCTION BOX: Group of electrical terminals

housed in protective box or container.

KATA THERMOMETER: Large bulb alcoholthermometer used to measure air velocities or

atmospheric conditions by means of cooling effect.

KELVIN SCALE (K): Thermometer scale on which

unit of measurement equals the centigrade degree andaccording to which absolute zero is 0 deg., the

equivalent of -273.16 deg. C. Water freezes at 273.16

deg. and boils at 373.16 deg.

KILOMETER: A metric unit of linear measurement =

1000 meters.

KILOWATT: Unit of electrical power, equal to 1000watts.

LACQUER: A protective coating or finish which driesto form a film by evaporation of a volatile constituent.

LAMPS, STERI: A lamp which gives forth a highintensity ultraviolet ray and is used to kill bacteria. It is

often used in food storage cabinets.

LAPPING: Smoothing a metal surface to highdegree of refinement or accuracy using a fine abrasive.

LATENT HEAT: Heat energy absorbed in process ofchanging form of substance (melting, vaporization,

fusion) without change in temperature or pressure.

LEAK DETECTOR: Device or instrument such as a

halide torch, an electronic sniffer; or soap solution used

to detect leaks.

LIMIT CONTROL: Control used to open or close

electrical circuits as temperature or pressure limits arereached.

LIQUID ABSORBENT; A chemical in liquid formwhich has the property to "take on" or absorb

moisture.

LIQUID INDICATOR: Device located in liquid line

which provides a glass window through which liquid

flow may be observed.

LIQUID LINE: The tube which carries liquid

refrigerant from the condenser or liquid receiver to therefrigerant control mechanism.

LIQUID NITROGEN: Nitrogen in liquid form whichis used as a low temperature refrigerant in chemical (or

expendable) refrigerating systems.

LIQUID RECEIVER: Cylinder connected tocondenser outlet for storage of liquid refrigerant in a

system.


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HVAC STEPS SAFE

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LIQUID-VAPOR VALVE REFRIGERANT

CYLINDER:A dual hand valve on a cylinder which isused to release either gas or liquid refrigerant from the

cylinder.

LITHARGE: Lead powder mixed with glycerine to sealpipe thread joints.

LIQUOR: Solution used in absorption refrigeration,

LITER: Metric unit of volume which equals 61, 03cubic inches.

LOW SIDE: That portion of a refrigerating systemwhich is under the lowest evaporating pressure.

LOW SIDE FLOAT VALVE: Refrigerant control valveoperated by level of liquid refrigerant in low pressure

side of system.

LOW SIDE PRESSURE: Pressure in cooling side ofrefrigerating cycle.

LOW SIDE PRESSURE CONTROL: Device used to

keep low side evaporating pressure from droppingbelow certain pressure.

LP FUEL: Liquefied petroleum which is used as a fuelgas.

LRA: Locked rotor amperes.

MAGNETIC CLUTCH: A device operated bymagnetism to connect or disconnect a power drive.

MAGNETIC FIELD: Space in which magnetic lines of

force exist.

MAGNETIC GASKET: A sealing material which

adheres due to small magnets inserted in gasket.

MAGNETISM: An electronic force which causes a

magnet to attract items made of steel.

MANIFOLD, SERVICE: A device equipped with

gauges and manual valves, used by serviceman to

service refrigerating systems.

MANOMETER: Instrument for measuring pressure

of gases 'and vapors. Gas pressure is balanced againstcolumn of liquid such as mercury, in U-shaped tube.

MASS: A quantity of matter cohering together tomake one body which is usually of indefinite shape.

MEAN EFFECTIVE PRESSURE (M.E.P.): Averagepressure on a surface when a changing pressure

condition exists.

MECHANICAL CYCLE: Cycle which is a repetitive

series of mechanical events.

MEGOHM: One megohm is equal to a million ohms.

MEGOHMMETER: An instrument for measuringextremely high resistances (In the millions of ohms

ranges).

MELTING POINT: Temperature at atmospheric

pressure, at which a substance will melt.

MERCOID BULB:An electrical circuit switch which

uses a small quantity of mercury in a sealed glass tubeto make or break electrical contact with terminals

within the tube.

METER: Metric unit of linear measurement equal to

39.37 inches.

METHANOL DRIER: Alcohol type chemical used tochange water in refrigerating system into a nonfreezing

solution.

METHYL CHLORIDE (R-40): A chemical once

commonly used as a refrigerant. The chemical formulais CH3CI. Cylinder color code is orange. The boiling

point at atmospheric pressure is -10, 4 F.

METRIC SYSTEM: A decimal system of measuresand weights, based on the meter and gram. Length of

one meter, 39.37 in.

MICRO: One millionth part of unit specified.MICROFARAD; Unit of condenser electrical capacity

equal to one millionth of a farad.

MICROMETER: A precision measuring instrument

used for making measurements accurate to .001 to.0001 in.

MICRON: Unit of length in metric system; a

thousandth part of one millimeter.

MICRON GAUGE: Instrument for measuring

vacuums very close to a perfect vacuum.

MILL me; acombining form denoting one thousandth;

example, milli volt, one thousandth of a volt.

MODULATING: A type of device or control whichtends to adjust by increments (minute changes) rather

than by either full on or full off operation.

MODULATING REFRIGERATION CYCLE:Refrigerating system of variable capacity,

MOISTURE DETERMINATION: An action usinginstruments and calculations to measure the relative or

absolute moisture in an air conditioned space.

MOISTURE INDICATOR: Instrument used to

measure moisture content of a refrigerant.

MOLECULE: Smallest portion of an element orcompound that retains chemical identity with the

substance m mass.

MOLLIERS DIAGRAM: Graph of refrigerant pressure,

heat and temperature properties.

MONEL: A trademark name for metal alloy consisting

chiefly of copper and nickel.

MONITOR TOP: Unit built by General Electric whichhad a cylindrical condenser surrounding the motor-

compressor, mounted on top of the cabinet,


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HVAC STEPS SAFE

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MONOCHLORODIFLUOROMETHANE: A refrigerant

better known as Freon 22 or R-22. Chemical formula isCHCIF2. Cylinder color code is green.

MOTOR - 2-POLE: A 3600 rpm electric motor

(synchronous speed).

MOTOR - 4-POLE: An 1800 rpm electric motor

(synchronous speed).

MOTOR, CAPACITOR: A single-phase inductionmotor with an auxiliary starting winding connected in

series with a condenser (capacitor) for better startingcharacteristics.

MOTOR BURNOUT: Condition in which the insulationof electric motor has deteriorated by overheating.

MOTOR CONTROL: Device to start ana/or stop a

motor at certain temperature or pressure conditions.

MOTOR STARTER: High capacity electric switches

usually operated by electromagnets.

MUFFLER, COMPRESSOR: Sound absorber chamberin refrigeration system used to reduce sound of gaspulsations.

MULLION: Stationary part of a structure between

two doors.

MULLION HEATER: An electrical heating element

mounted in the mullion and used to keep mullion from

sweating or frosting.

MULTIPLE EVAPORATOR SYSTEM: Refrigerating

system with two or more evaporators connected inparallel.

MULTIPLE SYSTEM: Refrigerating mechanism inwhich several evaporators are connected to one

condensing unit,

NATURAL CONVECTION: Movement of a fluidcaused by temperature differences (density changes).

NEOPRENE: A synthetic rubber which is resistant tohydrocarbon oil and gas.

NEUTRALIZER: Substance used to counteract acids,

in refrigeration system.

NEUTRON: That part of an atom core which has no

electrical potential; electrically neutral.

NO-FROST FREEZER:A low temperature refrigerator-cabinet in which no frost or ice collects on produce

stored in cabinet.

NOMINAL SIZE TUBING: Tubing measurement

which has an inside diameter the same as iron pipe ofthe same stated size.

NON-CODE INSTALLATION: A functionalrefrigerating system installed where there are no local,

state/ or national refrigeration codes in force.

NONCONDENSABLE GAS: Gas which does not

change into a liquid at operating temperatures andpressures.

NONFERROUS: Group of metals and metal alloyswhich contain no iron.

NONFROSTING EVAPORATOR:An evaporator which

never collects frost or ice on its surface.

NORMAL CHARGE: The thermal element charge

which is part liquid and part gas under all operatingconditions.

NORTH POLE, MAGNETIC: End of magnet fromwhich magnetic lines of force flow.

OFF CYCLE: That part of a refrigeration cycle when

the system is not operating.

OHM (R): Unit of measurement of electrical

resistance. One ohm exists when one volt causes a

flow of one ampere.

OHM METER: An instrument for measuring

resistance in ohms.

OHMS LAW: Mathematical relationship between

voltage/ current and resistance in an electric circuit,discovered by George Simon Ohm. It is stated as

follows: voltage (E = Amperes (I) x Ohms (R); or E = Ix R,

OIL BINDING: Physical condition when an oil layer on

top of refrigerant liquid hinders it from evaporating atits normal pressure-temperature condition.

OIL, REFRIGERATION: Specially prepared oil used inrefrigerator mechanism circulates to some extent with

refrigerant. The oil must be dry (entirely free ofmoisture), otherwise, moisture will condense out and

freeze in the refrigerant control and may cause

refrigerant mechanism to fail. An oil classified as re-frigerant oil must be free of moisture and othercontaminants.

OIL RINGS: Expanding rings mounted in grooves

and piston; designed to prevent oil from moving intocompression chamber.

OIL SEPARATOR: Device used to remove oil fromgaseous refrigerant.

OPEN CIRCUIT:An interrupted electrical circuit which

stops flow of electricity,OPEN DISPLAY CASE: Commercial refrigerator

designed to maintain its contents at refrigeratingtemperatures even though the contents are in an open

case.

OPEN TYPE SYSTEM: A refrigerating system which

uses a belt-driven compressor or a coupling-drivencompressor.

ORIFICE: Accurate size opening for controlling fluid

flow.


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HVAC STEPS SAFE

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OSCILLOSCOPE: A flourescent coated tube which

visually shows an electrical wave.

OVERLOAD: Load greater than load for whichsystem or mechanism was intended.

OVERLOAD PROTECTOR: A device, temperature,

pressure, or current operated/ which will stop

operation of unit if dangerous conditions arise.

OZONE: A gaseous form of oxygen usually obtainedby silent discharge of electricity in oxygen or air.

PARTIAL PRESSURES: Condition where two ormore gases occupy a space and each one creates part

of the total pressure.

PASCAL'S LAW: A pressure imposed upon a fluid is

transmitted equally in all directions.

PELETIER EFFECT: When direct current is passedthrough two adjacent metals one junction will become

cooler and the other will become warmer. This principle

is the basis of thermoelectric refrigeration.PERMANENT MAGNET: A material which has itsmolecules aligned and has its own magnetic field; bar

of metal which has been permanently magnetized.

PHOTOELECTRICITY: A physical action wherein anelectrical flow is generated by light waves.

PINCH-OFF^.TOOL: Device used to press walls of

tubing together until fluid flow ceases.

PISTON: Close fitting part which moves up and down

in a cylinder.

PISTON DISPLACEMENT: Volume displaced by

piston as it travels length of stroke.

PITOT TUBE: Tube used to measure air velocities.

PLENUM CHAMBER: Chamber or container for

moving air or other gas under a slight positive

pressure.

POLYPHASE MOTOR: Electrical motor designed to

be used with three-phase electrical circuit.

POLYSTYRENE: Plastic used as insulation in some

refrigerator cabinet structures.

PONDED ROOF: Flat roof designed to hold quantity of

water which acts as a cooling device.

PORCELAIN: Ceramic china-like coating applied to

steel surfaces.

POTENTIAL, ELECTRICAL: The electrical force which

moves, or attempts to move, electrons along aconductor or resistance.

POTENTIAL RELAY VOLTAGE: Electrical switchwhich is operated by voltage changes in electromagnet.

POTENTIOMETER: Instrument for measuring orcontrolling electrical potential.

POUR POINT (OIL): Lowest temperature at whichoil will pour or flow.

POWER: Time rate at which work is done or energyemitted; source or means of supplying energy.

POWER ELEMENT: Sensitive element of a

temperature operated control.

POWER FACTOR: Correction coefficient for AC

power necessary because of changing current andvoltage values.

PRESSURE: An energy impact on a unit area; forceor thrust exerted on a surface.

PRESSURE DROP: The pressure difference at two

ends of a circuit/ or part of a circuit, the two sides of afilter, or the pressure difference between the high side

and low side in a refrigerator mechanism.

PRESSURE LIMITER: Device which remains closeduntil a certain pressure is reached and then opens and

releases fluid to another part of system.PRESSURE-HEAT DIAGRAM: Graph of refrigerant

pressure, heat and temperature properties. (Mollier'sdiagram.)

PRESSURE MOTOR CONTROL: A device whichopens and closes an electrical circuit as pressures

change to desired pressures.

PRESSURE OPERATED ALTITUDE (POA) VALVE:Device which maintains a constant low side pressure

independent of altitude of operation.

PRESSURE REGULATOR, EVAPORATOR: An

automatic pressure regulating valve. Mounted insuction line between evaporator outlet and compressor

inlet. Its purpose is to maintain a predetermined

pressure and temperature in the evaporator,

PRESSURE SUCTION: Pressure in low pressure

side of a refrigerating system.

PRESSURE WATER VALVE: Device used to control

water flow which is responsive to head pressure ofrefrigerating system.

PRIMARY CONTROL: Device which directly controlsoperation of heating system.

PROCESS TUBE: Length of tubing fastened to

hermetic unit dome, used for servicing unit.

PROPANE: Volatile hydrocarbon used as a fuel, also

as a refrigerant.

PROTECTOR, CIRCUIT: An electrical device whichwill open an electrical circuit if excessive electricalconditions occur.

PROTON: Positive charged particle of an atom.

PSI: A symbol or initials used to indicate pressuremeasured in pounds per square inch.


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HVAC STEPS SAFE

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PSIA: A symbol or initials used to indicate pressure

measured in pounds per square inch absolute. Absolutepressure equals gauge pressure plus atmospheric pres-

sure,

P51G:A symbol or initials used to indicate pressure inpounds per square inch gauge. The "g" indicates that it

is gauge pressure and not absolute pressure.

PSYCHROMETER OR WET BULB HYGROMETER:An instrument for measuring the relative humidity ofatmospheric air.

PSYCHROMETRIC CHART: A chart that shows

relationship between the temperature, pressure andmoisture content of the air.

PSYCHROMETRIC MEASUREMENT: Measurement

of temperature pressure, and humidity using apsychrometric chart.

PULL DOWN: An expression indicating action ofremoving refrigerant from all or a part of refrigerating

system,

PUMP DOWN: The act of using a compressor or a

pump to reduce the pressure in a container or asystem.

PURGING: Releasing compressed gas to

atmosphere through some part or parts for the purposeof removing contaminants from that part or parts.

PYROMETER: Instrument for measuring hightemperatures.

QUENCHING: Submerging hot solid object in coolingfluid.

QUICK CONNECT COUPLING: A device which

permits easy, fast, connecting of two fluid lines.

R-11, TRICHLOROMONOFLUOROMETH-ANE: Lowpressure, synthetic chemical refrigerant which is also

used as a cleaning fluid.

R-12, DICHLORODIFLUOROMETHANE: A popular

refrigerant known as Freon 12.

R-22, MONOCHLORODIFLUOROMETH-ANE:

Synthetic chemical refrigerant.

R-40, Methyl Chloride: Refrigerant which was usedextensively in the 1920's and 1930's,

R-U3, TRICHLOROTRIFLUOROETHANE: Synthetic

chemical refrigerant.

R-160, ETHYL CHLORIDE: Refrigerant which is

seldom used at present time.

R-170, ETHANE: Low temperature application

refrigerant.

R-290, PROPANE: Low temperature application

refrigerant.

R-500: Refrigerant which is azeotropic mixture of R-

12 and R-152a.


22 and R-H5.


23 and R-13.

R-504: Refrigerant which is azeotropic mixture of R-32 and R-115.

R-600, BUTANE: Low temperature application

refrigerant; also used as a fuel.

R-611, METHYL FORMATE: Low pressure refrigerant.

R-717, AMMONIA: Popular refrigerant for industrialrefrigerating systems; also a popular absorption system

refrigerant.

R-764, SULPHUR DIOXIDE: Low pressure

refrigerant used extensively in 1920's and 1930*5. Not

in use at present; chemical is often used as anindustrial bleaching agent.

RADIAL COMMUTATOR: Electrical contact surfaceon a rotor which is perpendicular or at right angles to

the shaft center line.

RADIANT HEATING: Heating system in which

warm or hot surfaces are used to radiate heat into thespace to be conditioned.

RADIATION: Transfer of heat by heat rays.

RANGE: Pressure or temperature settings of a

control; change within limits.

RANKIN SCALE: Name given the absolute

(Fahrenheit) scale. Zero on this scale is -460 F.

RECEIVER-DRIER: A cylinder in a refrigerating

system for storing liquid refrigerant and which alsoholds a quantity of desiccant.

RECEIVER HEATING ELEMENT: Electrical resistance

mounted in or around liquid receiver, used to maintainhead pressures when ambient temperature is at

freezing or below freezing.

RECIPROCATING: Action in which the motion is

back and forth in a straight line.

RECORDING AMMETER: Electrical instrument

which uses a pen to record amount of current flow on

a moving paper chart.

RECORDING THERMOMETER: Temperature

measuring instrument which has a pen marking amoving chart.

RECTIFIER, ELECTRIC: An electrical device forconverting AC into DC.

REED VALVE: Thin flat tempered steel plate fastened

at one end.

REFRIGERANT: Substance used in refrigerating


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mechanism to absorb heat in evaporator coil by change

of state from a liquid to a gas, and to release its heatin a condenser as the substance returns from the

gaseous state back to a liquid state,

REFRIGERANT CHARGE: Quantity of refrigerant in asystem.

REFRIGERANT CONTROL: Device which metersrefrigerant and maintains pressure difference betweenhigh pressure and low pressure side of mechanical re-frigerating system while unit is running.

REGISTER: Combination gri He and damper

assembly covering on an air opening or end of an airduct.

RELATIVE HUMIDITY: Ratio of amount of water

vapor present in air to greatest amount possible atsame temperature.

RELAY: Electrical mechanism which uses smallcurrent in control circuit to operate a valve switch in

operating circuit.

RELIEF VALVE: Safety device designed to open

before dangerous pressure is reached,

REMOTE POWER ELEMENT CONTROL: Device

with sensing element located apart from operating

mechanism.

REMOTE SYSTEM: Refrigerating system which has

condensing unit located outside and separate fromrefrigerator cabinet.

REPULSION-START INDUCTION MOTOR: Typeof motor which has an electrical winding on the

rotor for starting purposes.

RESISTANCE, (R) ELECTRICAL: The difficultyelectrons encounter moving through a conductor or

substance.

REVERSE CYCLE DEFROST: Method of heatingevaporator for defrosting purposes by using valves to

move hot gas from compressor into evaporator.

REVERSING VALVE: Device used to reverse

direction of the refrigerant flow depending uponwhether heating or cooling is desired,

RINGELMANN SCALE: Measuring device for

determing smoke density.RISER VALVE: Device used to manually control flow

of refrigerant in vertical piping.

ROTARY BLADE COMPRESSOR: Mechanism for

pumping fluid by revolving blades inside cylindricalhousing.

ROTARY COMPRESSOR: Mechanism which pumpsfluid by using rotating motion.

ROTOR: Rotating part of a mechanism.

RUNNING WINDING: Electrical winding of motorwhich has current flowing through it during normaloperation of motor.

SADDLE VALVE (TAP-A-LINE):Valve body shaped

so it may be silver brazed to refrigerant tubing surface.

SAFETY CONTROL: Device which will stop the

refrigerating unit if unsafe pressures ana/ortemperatures are reached.

SAFETY MOTOR CONTROL: Electrical device used

to open circuit if the temperature, pressure, ana/or 'the current flow exceed safe conditions.

SAFETY PLUG: Device which will release the contentsof a container above normal pressure conditions and

before rupture pressures are reached.

SATURATION: Condition existing when substancecontains maximum of another substance for that

temperature and pressure.

SCAVENGER PUMP: Mechanism used to removefluid from sump or container.

SCHRADER VALVE: Spring loaded device whichpermits fluid flow in one direction when a center pin is

depressed; in other direction when a pressuredifference exists.

SCOTCH YOKE: Mechanism used to change

reciprocating motion into rotary motion or vice-versa.Used to connect crankshaft to piston in refrigerationcompressor.

SEALED UNIT: (See Hermetic System.) A motor-

compressor assembly inwhich motor and compressor

operate inside sealed dome or housing.

SEAL LEAK: Escape of oil ano/or refrigerant at the

junction where shaft enters housing.

SEAL, SHAFT: A device used to prevent leakage

between shaft and housing.

SECONDARY REFRIGERATING SYSTEM:

Refrigerating system in which condenser is cooled byevaporator of another or primary refrigerating system.

SECOND LAW OF THERMODYNAMICS: Heat willflow only from material at certain temperature to

material at lower temperature,

SEEBECK EFFECT: When two different adjacentmetals are heated, an electric current is generated.

SELF-INDUCTANCE: Magnetic field induced inconductor carrying the current.

SEMICONDUCTOR: A material that has electricalproperties of current Low, between a conductor and an

insulator.

SENSIBLE HEAT: Heat which causes a change intemperature of a substance.


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SENSOR: A material or device which goes through a

physical change or an electronic characteristic changeas the conditions change.

SEPARATOR, OIL: A device used to separate

refrigerant oil from refrigerant gas and return the oil tocrankcase of compressor.

SEQUENCE CONTROLS: Group of devices which actin series or in time order.

SERVEL SYSTEM: One type of continuous operation

absorption refrigerating system,

SERVICEABLE HERMETIC: Hermetic unit housing

containing motor and compressor assembled by use ofbolts or threads.

SERVICE VALVE: A device to be attached to system

which provides opening for gauges ana/or charginglines. Also provides means of shutting off or opening

gauge and charging ports, and controlling refrigerantflow in system.

SHADED POLE MOTOR: A small AC motor used forlight start loads. Has no brushes or commutator.

SHARP FREEZING: Refrigeration at temperatureslightly below freezing, with moderate air circulation.

SHELL-AND-TUBE FLOODED EVAPORATOR:

Device/which flows water through tubes built intocylindrical evaporator or vice-versa.

SHELL TYPE CONDENSER: Cylinder or receiver

which contains condensing water coils or tubes.

SHORT CIRCUIT:An electrical condition where part

of circuit touches another part of circuit and causes allor part of current to take wrong path.

SHORT CYCLING: Refrigerating system that starts

and stops more frequently than it should.

SHROUD: Housing over condenser or evaporator.

SIGHT GLASS: Glass tube or glass window inrefrigerating mechanism which shows amount of

refrigerant, or oil in system; or, pressure of gasbubbles in liquid tine.

SILICA GEL: Chemical compound used as a drier,

which has ability to absorb moisture when heated,moisture is released and compound may be reused.

SILICON CONTROLLED RECTIFIER (SCR):

Electronic semiconductor which contains silicon.

SILVER BRAZING: Brazing .process in which

brazing alloy contains some silver as part of joiningalloy.

SINE WAVE, AC CURRENT: Wave form of singlefrequency alternating current; wave whose

displacement is sine of angle proportional to time ordistance.

SINGLE-PHASE MOTOR: Electric motor whichoperates on single-phase alternating current.

SINGLE-POLE, DOUBLE-THROW SWITCH, SPOT:Electric switch with one blade and two contact points.

SINGLE-POLE, SINGLE-THROW SWITCH, SPST:

Electric switch with one blade and one contact point.

SINTERED OIL BEARING: Porous bearing metal,

usually bronze, and which has oil in pores of bearingmetal.

SLING PSYCHROMETER: Humidity measuringdevice with wet and dry bulb thermometers/which is

moved rapidly through air when measuring humidity.

SLUG: A unit of mass equal to the weight (Englishunits) of object divided by 32.2 (acceleration due to the

force of gravity).

SMOKE TEST: Test made to determine completenessof combustion.

SOLAR HEAT: Heat from visible and invisible energywaves from the sun.

SOLDERING: Joining two metals by adhesion of alow melting temperature metal (less than 800 F.).

SOLENOID VALVE: Electromagnet with a movingcore which serves as a valve, or operates a valve.

SOLID ABSORBENT REFRIGERATIONrefrigerating system which uses solid substance asabsorber of the refrigerant during cooling part of cycle

and releases refrigerant when heated duringgenerating part of cycle.

SOUTH POLE, MAGNETIC: That part of magnet intowhich magnetic flux lines flow.

SPECIFIC GRAVITY: Weight of a liquid compared to

water which is assigned value of 1.0.

SPECIFIC HEAT: Ratio of quantity of heat required toraise temperature of a body one-degree to that

required to raise temperature of equal mass of waterone degree,

SPECIFIC VOLUME: Volume per unit mass of asubstance.

SPLASH SYSTEM, OILING: Method of lubricating

moving parts by agitating or splashing oil.SPLIT-PHASE MOTOR: Motor with two stator

windings. Winding in use while starting is disconnectedby centrifugal switch after motor attains speed, and

then motor operates on other winding.

SPLIT SYSTEM: Refrigeration or air conditioning

installation which places condensing unit outside orremote from evaporator. Also applicable to heat pump

installations.

SPRAY COOLING: Method of refrigerating by


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spraying refrigerant inside of evaporator or by spraying

refrigerated water.

SQUIRREL CAGE: Fan which has blades parallel tofan axis and moves air at right angles or perpendicular

to fan axis.

STANDARD ATMOSPHERE: Condition when air is at

14.7 psia pressure, at 59 F. temperature.

STANDARD CONDITIONS: Used as a basis for airconditioning calculations. Temperature of 68 degrees

F., pressure of 29.92 inches of Hg and relative humidityof 30 percent.

STARTING RELAY: An electrical device whichconnects and/or disconnects starting winding of electric

motor.

STARTING WINDING: Winding in electric motorused only during brief period when motor is starting.

STATIONARY BLADE COMPRESSOR: A rotary

pump which uses blade inside pump to separate intakechamber from exhaust chamber.

STATOR, MOTOR: Stationary part of electric motor.

STEAM: Water in vapor state.

STEAM HEATING: Heating system inwhich steamfrom a boiler is conducted to radiators in space to be

heated.

STEAM JET REFRIGERATION: Refrigerating systemwhich uses a steam venturi to create high vacuum (low

pressure) on a water container causing water to evap-orate at low temperature.

5TELLITE: Trade name for metal alloy which isvery hard.

STETHOSCOPE: Instrument used to detect sounds.

STOKER: Machine used to supply a furnace with

coal.

STRAINER: Device such as a screen or filter used to

retain solid particles while liquid passes through.

STRATIFICATION OF AIR: Condition in which there

is little or no air movement in room; air lies intemperature layers.

STRIKE: Door part of a door latch.

SUBCOOLING: Cooling of liquid refrigerant below its

condensing temperature.

SUBLIMATION: Condition where a substance

changes from a solid to a gas without becoming aliquid.

SUCTION LINE: Tube or pipe used to carryrefrigerant gas from evaporator to compressor.

SUCTION PRESSURE CONTROL VALVE: Devicelocated in the suction line which maintains constant

pressure in evaporator during running portion of cycle.

SUCTION SERVICE VALVE: A two-way manual-

operated valve located at the inlet to compressor,which controls suction gas flow and is used to service

unit.

SULFUR DIOXIDE: Gas once commonly used as a

refrigerant. Refrigerant number is R-764; chemicalformula is S02. Cylinder color code/ black; boiling pointat atmospheric pressure 14 F.

SUPERHEAT: Temperature of vapor above boilingtemperature of its liquid at that pressure.

SUPERHEATER: Heat exchanger arranged to coolliquid going to evaporator using this heat to superheat

vapor leaving evaporator.

SURFACE PLATE: Tool with a very accurate flatsurface, used for measuring purposes, and for lapping

flat surfaces.

SURGE: Modulating action of temperature orpressure before it reaches its final value or setting.

SURGE TANK: Container connected to a refrigeratingsystem which increases gas volume and reduces rate of

pressure change.

SWAGING: Enlarging one tube end so end of other

tube of same size will fit within.

SWASH PLATE-WOBBLE PLATE: Device used tochange rotary motion to reciprocating motion, used in

some refrigeration compressors.

SWEATING: This term is^ used two different ways

in refrigeration work: l-Condensation of moisture fromair on cold surface. 2-Method of soldering in which the

parts to be joined are first coated with a thin layer of

solder.

SWEET WATER: Term sometimes used to describe

tap water.

SYLPHON SEAL: Corrugated metal tubing used to

hold seal ring and provide leak-proof connectionbetween seal ring and compressor body or shaft,

SYNTHETIC RUBBER, NEOPRENE: Soft resilientmaterial made of a synthetic chemical compound.

TAP-A-LINE: Device used to puncture or tap a line

where there are no service valves available; sometimescalled a saddle valve.

TAP DRILL: Drill used to form hole prior to placingthreads in hole. The drill is the size of the root

diameter of tap threads.

TAP (SCREW THREAD): Tool used to cut internal

threads.

TEFLON: Synthetic rubber material often used for 0rings.


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TEMPERATURE: Degree of hotness or coldness as

measured by a thermometer; measurement of speed ofmotion of molecules.

TEMPERATURE HUMIDITY INDEX: Actual

temperature and humidity of sample of air, comparedto air at standard conditions.

TEST LIGHT: Light provided with test leads, used totest or probe electrical circuits to determine if they arealive.THERM: Quantity of heat equivalent to 100,000Btu.

THERMAL RELAY (HOT WIRE RELAY): Electrical

control used to actuate a refrigeration system. Thissystem uses a wire to convert electrical energy intoheat energy.

THERMISTOR: Material called a semiconductor,which is between a conductor and an insulator, whichhas electrical resistance that varies with temperature.

THERMOCOUPLE: Device which generates electricity,

using principle that if two dissimilar metals are weldedtogether and junction is heated, a voltage will develop

across open ends.

THERMOCOUPLE THERMOMETER: Electrical

instrument using thermocouple as source of electrical

flow, connected to Liam meter calibrated intemperature degrees.

THERMODISK DEFROST CONTROL: Electricalswitch with bimetal disk which is controlled by electrical

energy.

THERMODYNAMICS: Science which deals with

mechanical action or relations of heat.

THERMOELECTRIC REFRIGERATION: A

refrigerator mechanism which depends on Peletier

effect. Direct current flowing through electrical junctionbetween dissimilar metals provides heating or cooling

effect depending on direction of flow of current.

THERMOMETER: Device for measuring

temperatures.

THERMOMODULE: Number of thermocouples used

in parallel to achieve low temperatures.

THERMOSTAT: Device responsive to ambienttemperature' conditions.

THERMOSTATIC CONTROL: Device which operates-

system or part of system based on temperaturechanges.

THERMOSTATIC EXPANSION VALVE: A controlvalve operated by temperature and pressure within

evaporator coil, which controls flow of refrigerant.Control bulb is attached to outlet of coil.

THERMOSTATIC MOTOR CONTROL: Device used to

control cycling of unit through use of control bulbattached to evaporator.

THERMOSTATIC VALVE: Valve controlled bythermostatic elements.

THERMOSTATIC WATER VALVE: Valve used tocontrol flow of water through system, actuated by

temperature difference. Used in units such as water-

cooled compressor or condenser.

THREE-PHASE: Operating by means of combinationof three alternating current circuits which differ inphase by one third of a cycle.

THROTTLING: Expansion of gas through orifice orcontrolled opening without gas performing any work m

expansion process.

TIMERS: Mechanism used to control on and off

times of an electrical circuit.

TIMER-THERMOSTAT: Thermostat control whichincludes a clock mechanism. Unit automatically controls

room temperature and changes it according to time ofday.

TON OF REFRIGERATION: Refrigerating effect equalto the melting of one ton of ice in 24 hours. This may

be expressed as follows:

288,000 Btu/24 hours 12,000 Btu/1 hour 200Btu/minute

TON REFRIGERATION UNIT: Unit which removes

same amount of heat in 24 hours as melting of one tonof ice.

TORQUE: Turning or twisting force.

TORQUE WRENCHES: Wrench which may be used to

measure torque or pressure applied to a nut or bolt.

TRANSDUCER: Device actuated by power from one

system and supplies power in another form to second

system.

TRANSFORMER: Device which transfers electrical

energy from primary circuit, into variations of voltagein secondary circuit, by electromagnetic induction.

TRANSFORMER-RECTIFIER: Combination

transformer and rectifier in which input in AC may bevaried and then rectified into DC.

TRANSISTOR: Electronic device commonly used foramplification, similar in use to electron tube. Depends

on conducting properties of semiconductors in whichelectrons moving in one direction are considered as

leaving holes that serve as carriers of positiveelectricity inapposite direction.

TRICHLOROTRIFLUOROETHANE: Complete nameof refrigerant R-113

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6666278 Glossary of Technical Terms Steps