Glossary of Terms I to Z

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 for storage of ice cream.

Ice Melting Equivalent (I.M.E.) (Ice Melting Effect)-Amount of heat absorbed by melting ice at 32 F. is 144 Btu per pound of ice or 288,000 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 many heating systems to ignite fuel.

Impeller-Rotating part of a centrifugal pump.

Induced Magnetism-Ability of a magnetic field to produce magnetism in a metal.

Induction Motor-An AC motor which operates on principle of rotating magnetic field. Rotor has no electrical 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 the visible spectrum.

Insulation, Thermal-Substance used to retard or 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 a circuit expressed in amperes x resistance (I x R) or voltage drop.

Isothermal-Changes of volume or pressure under conditions of constant temperature.

Isothermal Expansion And Contraction-An action which takes place without a temperature change.


Joule-Thomson Effect-Change in temperature of a gas on expansion through a porous plug from a high 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 alcohol thermometer 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 and according to which absolute zero is 0 deg., the equivalent of -271.16 deg. C. Water freezes at 273.16 deg. and boils at 373.16 deg.

Kilometer-Unit of electrical power, equal to 1000 watts.


Lacquer-A protective coating or finish which dries to form a film by evaporation of a volatile constituent.

Lamps, Steri-A lamp which gives forth a high intensity ultraviolet ray and is used to kill bacteria. It is often used in food storage cabinets.

Lapping-Smoothing a metal surface to high degree of refinement or accuracy using a fine abrasive.

Latent Heat-Heat energy absorbed in process of changing 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 are reached.

Liquid Absorbent-A chemical in liquid form which 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 of liquid receiver to the refrigerant control mechanism.

Liquid Nitrogen-Nitrogen in liquid form which is used as a low temperature refrigerant in chemical (or expendable) refrigerating systems.

Liquid Receiver-Cylinder connected to condenser outlet for storage of liquid refrigerant in a system.

Liquid-Vapor Valve Refrigerant Cylinder-A dual hand valve on refrigerant cylinders which is used to release either gas or liquid refrigerant from the cylinder.

Litharge-Lead powder mixed with glycerine to seal pipe thread joints.

Liquor-Solution used in absorption refrigeration.

Liter-Metric unit of volume which equals 71.03 cubic inches.

Low Side-That portion of a refrigerating system which is under the lowest evaporating pressure.

Low Side Float Valve-Refrigerant control valve operated by level of liquid refrigerant in low pressure side of system.

Low Side Pressure-Pressure in cooling side of refrigerating cycle.

Low Side Pressure Control-Device used to keep low side evaporating pressure from dropping below certain pressure.

LP Fuel-Liquefied petroleum which is used as a fuel gas.


Magnetic Clutch-A device operated by magnetism to connect or disconnect a power drive.

Magnetic Field-Space in which magnetic lines of force exists.

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 against column of liquid such as mercury, in U-shaped tube.

Mass-A quantity of matter cohering together to make one body which is usually of indefinite shape.

Mean Effective Pressure (M.E.P.)-Average pressure 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 measuring extremely high resistances (in the millions of ohms ranges).

Melting Point-Telperature 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 tube to make of break electrical contract with terminals within the tube.

Meter-Metric unit of linear measurement equal to 39.37 inches.

Methanol Drier-Alcohol type chemical used to change water in refrigerating system into a nonfreezing solution.

Methyl Chloride (R-40)-A chemical once commonly used as a refrigerant. The chemical formula is CH3CL. Cylinder color code is orange. The boiling point at atmospheric pressure is -10.4 F.

Metric System-A decimal system of measures and 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.

Milli-A combining form denoting one thousandth; example, millivolt,one thousandth of a volt.

Modulating-A type of device or control which tends 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 using instruments 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 of compound that retains chemical identity with the substance in mall.

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 which had a cylindrical condenser surrounding the motor-compressor, mounted on top of the cabinet.

Monochlorodifluoromethane-A refrigerant better known as Freon 12 or R-22. Chemical formula is CHCIP2. Cylinder color code is green.

Motor-2-Pole-A 3,600 rpm electric motor (synchronous speed).

Motor-4-Pole-A 1,800 rpm electric motor (synchronous speed).

Motor, Capacitor-A single-phase induction motor with an auxiliary starting winding connected in series with a condenser (capacitor) for better starting characteristics.

Motor Burnout-Condition in which the insulation of electric motor has deteriorated by overheating.

Motor Control-Device to start and/or stop a motor at certain temperature or pressure conditions.

Motor Starter-High capacity electric switches usually operated by electromagnets.

Muffler, Compressor-Sound absorber changer in refrigeration system used to reduce sound of gas pulsations.

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 and frosting.

Multiple Evaporator System-Refrigerating system with two or more evaporators connected in parallel.

Multiple System-Refrigerating mechanism in which several evaporators are connected to one condensing unit.


Natural Convection-Movement of a fluid caused by temperature differences (density changes).

Neoprene-A synthetic rubber which is resistant to hydrocarbon 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 stared in cabinet.

Nominal Size Tubing-Tubing measurement which has an inside diameter the same as iron pipe of the same stated size.

Non-Code Installation-A functional refrigerating 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 and pressures.

Nonferrous-Group of metals and metal alloys which 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 operating conditions.

North Pole, Magnetic-End of magnet from which 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.

Ohmmeter-An instrument for measuring resistance in ohms.

Ohms Law-Mathematical relationships 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 = I x R.

Oil Binding-Physical condition when an oil layer on top of refrigerant liquid hinders it from evaporating at its normal pressure-temperature condition.

Oil, Refrigeration-Specially prepared oil used in refrigerator mechanism circulates to some extent with refrigerant. The oil must be dry (entirely free of moisture), otherwise, moisture will control and may cause refrigerant mechanism to fail. An oil classified as a refrigerant oil must be free of moisture other contaminants.

Oil Rings-Expanding rings mounted in grooves and piston; designed to prevent oil from moving into compression chamber.

Oil Separator-Device used to remove oil from gaseous refrigerant.

Open Circuit-An interrupted electrical circuit which stops flow of electricity.

Open Display Case-Commercial refrigerator designed to maintain its contents at refrigerating temperatures even though the contents are in an open case.

Open Type System-A refrigerating system which uses a belt-driven compressor or a coupling-driven compressor.

Orifice-Accurate size opening for controlling fluid flow.

Oscilloscope-A fluorescent coated tube which visually shows an electrical wave.

Overload-Load greater than load for which system or mechanism was intended.

Overload Protector-A device, either temperature, pressure, or current operated, which will stop operation of unit if dangerous conditions arise.

Ozone-A gaseous form of oxygen usually obtained by silent discharge of electricity on oxygen or air.


Partial Pressures-Condition where two or more 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 passes through two adjacent metals one junction will become warmer. This principle is the basis of thermoelectric refrigeration.

Permanent Magnet-A material which has its molecules aligned and has its own magnetic field; bar of metal which has been permanently magnetized.

Photoelectricity-A physical action wherein an electrical flow is generated by light waves.

Pinch-Off Tool-Device used to press walls of a 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 an 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 a conductor or resistance.

Potential Relay Voltage-Electrical switch which is operated by voltage changes in electromagnet.

Potentiometer-Instrument for measuring or controlling electrical potential.

Pour Point (Oil)-Lowest temperature at which oil will pour or flow.

Power-Time rate at which work is done or energy emitted; 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 and voltage values.

Pressure-An energy impact on a unit area; force or 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 a filter, or the pressure difference between the high side and low side in a refrigerator mechanism.

Pressure Limiter-Device which remains closed until 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's diagram.)

Pressure Motor Control-A device which opens 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 in suction 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 of refrigerating system.

Primary Control-Device which directly controls operation 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 which will open an electrical circuit if excessive electrical conditions occur.

Proton-Positive charged particle of an atom.

PSI-A symbol or initials used to indicate pressure measured in pounds per square inch.

PSIA-A symbol or initials used to indicate pressure measured in pounds per square inch absolute. Absolute pressure equals gauge pressure plus atmospheric pressure.

PSIG-A symbol or initials used to indicate pressure in pounds per square inch gauge. The "g" indicated that it is gauge pressure and not absolute pressure.

Psychrometer Or Wet Bulb Hygrometer-An instrument for measuring the relative humidity of atmospheric air.

Psychrometric Chart-A chart that shows relationship between the temperature, pressure and moisture content of the air.

Psychrometric Measurement-Measurement of temperature pressure, and humidity using a psychrometric chart.

Pull Down-An expression indicating action of removing 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 a system.

Purging-Releasing compressed gas to atmosphere through some part or parts for the purpose of removing contaminants from that part or parts.

Pyrometer-Instrument for measuring high temperatures.


Quenching-Submerging hot solid object in cooling fluid.

Quick Connect Coupling-A device which permits easy, fast, connecting of two fluid lines.


R-11, Trichloromonofluoromethane-Low pressure, synthetic chemical refrigerant which is also used as a cleaning fluid.

R-12, Dichlorodiflouromethane-A popular refrigerant known as Freon 12.

R-22, Monochlorodifluoromethane-Synthetic chemical refrigerant.

R-40, Methyl Chloride-Refrigerant which was used extensively in the 1920's and 1930's.

R-113, 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.

R-502-Refrigerant which is azeotropic mixture of R-22 and R-115.

R-503-Refrigerant which is azeotropic mixture of R-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 industrial refrigerating systems; also a popular absorption system refrigerant.

R-764, Sulphur Dioxide-Low pressure refrigerant used extensively in the 1920's and 1930's. Not in use at present; chemical is often used as an industrial bleaching agent.

Radial Commutator-Electrical contact surface on 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 the space 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 also holds a quantity of desiccant.

Receiver Heating Element-Electrical resistance mounted in or around liquid receiver, used to maintain head 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 used a pen to record amount of current flow on a moving paper chart.

Recording Thermometer-Temperature measuring instrument which has a pen marking a moving chart.

Rectifier, Electric-An electrical device for converting AC into DC.

Reed Valve-this flat tempered steed plate fastened at one end.

Refrigerant-Substance used in refrigerating mechanism to absorb heat in evaporator coil by change of state from a liquid to a gas, and to release its heat in condenser as the substance returns from the gaseous state back to a liquid state.

Refrigerant Charge-Quantity of refrigerant in a system.

Refrigerant Control-Device which meters refrigerant and maintains pressure difference between high pressure and low pressure side of mechanical refrigerating system while unit is running.

Register-Combination grille and damper assembly covering on an air opening or end of an air duct.

Relative Humidity-Ratio of amount of water vapor present in air to greatest amount possible at same temperature.

Relay-Electrical mechanism which uses small current 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 from refrigerator cabinet.

Repulsion-Start Induction Motor-Type of motor which has an electrical winding on the rotor for starting purposes.

Resistance, (R) Electrical-The difficulty electrons encounter moving through a conductor or substance.

Reverse Cycle Defrost-Method of heating evaporator 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 upon whether heating or cooling is desired.

Ringlemann Scale-Measuring device for determining 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 cylindrical housing.

Rotary Compressor-Mechanism which pumps fluid by using rotating motion.

Rotor-Rotating part of a mechanism.

Running Winding-Electrical winding of motor which has current flowing through it during normal operation 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 and/or temperatures are reached.

Safety Motor Control-Electrical device used to open circuit if the temperature, pressure, and/or the current flow exceed safe conditions.

Safety Plug-Device which will release the contents of a container above normal pressure conditions and before rupture pressures are reached.

Saturation-Condition existing when substance contains maximum of another substance for that temperature and pressure.

Scavenger Pump-Mechanism used to remove fluid from sump or container.

Schrader Valve-Spring loaded device which permits fluid flow in one direction when a center pin is depressed; in other direction when a pressure difference exists.

Scotch Yoke-Mechanism used to change reciprocating motion into rotary motion or vice-versa. Used to connect crankshaft to piston in refrigeration compressor.

Sealed Unit-(See Hermetic System.) A motor-compressor assembly in which motor and compressor operate inside sealed dome or housing.

Seal Leak-Escape of oil and/or refrigerant at the junction where shaft enters housing.

Seal, Shaft-A device used to prevent leakage between shaft and housing.

Seasonal Energy Efficiency Ratio(SEER)-the total cooling of a central unitary air conditioner or unitary heat pump in BTU's during its normal annual usage period for cooling divided by; the total electric energy input in watt-hours during the same period.

Secondary Refrigerating System-Refrigerating system in which condenser is cooled by evaporator of another or primary refrigerating system.

Second Law Of Thermodynamics-Heat will flow only from material at certain temperature to material at lower temperature.

Seebeck Effect-When two different adjacent metals are heated, an electric current is generated.

Self-Inductance-Magnetic field induced in conductor and an insulator.

Sensible Heat-Heat which causes a change in temperature of a substance.

Sensor-A material or device which goes through a physical change or an electronic characteristic change as the conditions change.

Separator, Oil-A device used to separate refrigerant oil from refrigerant gas and return the oil to crankcase of compressor.

Servel System-One type of continuous operation absorption refrigerating system.

Serviceable Hermetic-Hermetic unit housing containing motor and compressor assembled by use of bolts or threads.

Service Valve-A device to be attached to system which provides opening for gauges and/or charging lines. Also provides means of shutting off or opening gauge and charging ports, and controlling refrigerant flow in system.

Shaded Pole Motor-A small AC motor used for light start loads. Has no brushes or commutator.

Shell-And-Tube Flooded Evaporator-Device which flows water through tubes built into cylindrical 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 a circuit touches another part of circuit and causes all or 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 in refrigerating mechanism which shows amount of refrigerant, or oil in system; or, pressure of gas bubbles in liquid line.

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 joining alloy.

Sine Wave, AC Current-Wave form of single frequency alternating current; wave whose displacement is sine of angle proportional to time or distance.

Single-Phase Motor-Electric motor which operates on single-phase alternating current.

Single-Pole, Double-Throw Switch, SPDT-Electric switch with one blade and two contact point.

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 pores of bearing metal.

Sling Psychrometer-Humidity measuring device with wet and dry bulb thermometers, which is moved rapidly through air when measuring humidity.

Slug-A unit of mass equal to the weight (English units) of object divided by 32.2 (acceleration due to the force of gravity).

Smoke Test-Test made to determine completeness of combustion.

Solar Heat-Heat from visible and invisible energy waves from the sun.

Soldering-Joining two metals by adhesion of a low melting temperature metal (less than 800 F. ).

Solenoid Valve-Electromagnet with a moving core which serves as a valve, or operates a valve.

Solid Absorbent Refrigeration-Refrigerating system which used solid substance as absorber of the refrigerant during cooling part of cycle and releases refrigerant when heated during generating part of cycle.

Sound Rating(SR)-is a tone corrected A-weighted sound power level expressed in decibels. The Sound Rating is based on tests performed at Standard Rating Conditions (cooling).

South Pole, Magnetic-That part of magnet into which 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 to raise temperature of a body one-degree to that required to raise temperature of equal mass of water one degree.

Specific Volume-Volume per unit mass of a substance.

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 disconnected by centrifugal switch after motor attains speed, then motor operates on other winding.

Split System-Refrigeration or air conditioning installation which places condensing unit outside or remote from evaporator. Also applicable to heat pump installations.

Spray Cooling-Method of refrigerating by spraying refrigerant inside of evaporator or by spraying refrigerated water.

Squirrel Cage-Fan which has blades parallel to fan axis and moves air at right angles or perpendicular to fan axis.

Standard Atmosphere-Condition when air is at 14.7 psia pressure, at 68 F. temperature.

Standard Conditions-Used as a basis for air conditioning calculations. Temperature of 68 degrees F., pressure of 29.92 inches of Hg and relative humidity of 30 percent.

Starting Relay-An electrical device which connects and/or disconnects starting winding of electric motor.

Starting Winding-Winding in electric motor used only during brief period when motor is starting.

Stationary Blade Compressor-A rotary Pump which uses blade inside pump to separate intake chamber from exhaust chamber.

Stator, Motor-Stationary part of electric motor.

Steam-Water in vapor state.

Steam Heating-Heating system is which steam from a boiler is conducted to radiators in space to be heated.

Steam Jet Refrigeration-Refrigerating system which uses a steam venturi to create high vacuum (low pressure) on a water container causing water to evaporate at low temperature.

Stellite-Trade name for metal alloy which is very 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 in temperature 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 a liquid.

Suction Line-Tube or pipe used to carry refrigerant gas from evaporator to compressor.

Suction Pressure Control Valve-Device located 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; chemical formula is SO2. Cylinder color code, black; boiling point at atmospheric pressure 14F.

Superheat-Temperature of vapor above boiling temperature of its liquid at that pressure.

Superheater-Heat exchanger arranged to cool liquid going to evaporator using this heat to superheat vapor leaving evaporator.

Surface Plate-Tool with a very accurate flat surface, used for measuring purposes, and for lapping flat surfaces.

Surge-Modulating action of temperature or pressure before it reaches its final value or setting.

Surge Tank-Container connected to a refrigerating system 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 to change rotary motion to reciprocating motion, used in some refrigeration compressors.

Sweating-This term is used two different ways in refrigeration work: 1-Condensation of moisture from air 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 leakproof connection between seal ring and compressor body or shaft.

Synthetic Rubber, Neoprene-Soft resilient material made of a synthetic chemical compound.


Tap-A-Line-Device used to puncture or tap a line where there are no service valves available; sometimes called a saddle valve.

Tap Drill-Drill used to form hole prior to placing threads 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 O rings.

Temperature-Degree of hotness or coldness as measured by a thermometer; measurement of speed of motion of molecules.

Temperature Humidity Index-Actual temperature and humidity of sample of air, compared to air at standard conditions.

Test Light-Light provided with test leads, used to test or probe electrical circuits to determine if they are alive.

Therm-Quantity of heat equivalent to 100,000 Btu.

Thermal Relay (Hot Wire Relay)-Electrical control used to actuate a refrigeration system. This system used a wire to convert electrical energy into heat energy.

Thermistor-Material called a semiconductor, which is between a conductor and an insulator, which has electrical resistance that varies with temperature.

Thermocouple-Device which generates electricity, using principle that if two dissimilar metals are welded together and junction is heated, a voltage will develop across open ends.

Thermocouple Thermometer-Electrical instrument using thermocouple as source of electrical flow, connected to source of electrical flow, connected to milliammeter calibrated in temperature degrees.

Thermodisk Defrost Control-Electrical switch with bimetal disk with 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 similar 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 ambient temperature conditions.

Thermostatic Control-Device which operates system or part of system bases on temperature changes.

Thermostatic Expansion Valve-A control valve 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 bulb attached to evaporator.

Thermostatic Valve-Valve controlled by thermostatic elements.

Thermostatic Water Valve-Valve used to control 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 combination of three alternating current circuits which differ in phases by one third of a cycle.

Throttling-Expansion of gas through orifice or controlled opening without gas performing any work in expansion process.

Timers-Mechanism used to control on and off times of an electrical circuit.

Timer-Thermostat-Thermostat control which includes a clock mechanism. Unit automatically controls room temperature and changes it according to time of day.

Ton Of Refrigeration-Refrigerating effect equal to the melting of one tone of ice in 24 hours. This may be expressed as follows: 288,000 Btu/24 hours or 12,000 Btu/1 hour or 200 Btu/minute.

Ton of Refrigeration Unit-Unit which removes same amount of heat in 24 hours as melting one tone of 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 voltage in secondary circuit, by electromagnetic induction.

Transformer-Rectifier-Combination transformer and rectifier in which input in AC may be varied and then rectified into DC.

Transistor-Electronic device commonly used for amplification, similar in use to electron tube. Depends on conducting properties of semiconductors in which electrons moving in one direction are considered as leaving holes that serve as carriers of positive electricity in opposite direction.

Trichlorotrifluoroethane-Complete name of refrigerant R-113. Group 1 refrigerant in rather common use. Chemical compounds which make up this refrigerant are chlorine, fluorine, and ethane.

Triple Point-Pressure temperature condition in which a substance is in equilibrium in solid, liquid and vapor states.

Truck, Refrigerated-Commercial vehicle equipped to maintain below atmospheric temperatures.

Tube, Constricted-Tubing that is reduced in diameter.

Tube-Within-A-Tube-A water-cooled condensing unit in which a small tube is placed inside large unit. Refrigerant passes through one tube; water through the other.

Tubing-Fluid carrying pipe which has a thin wall.

Two-Temperature Valve-Pressure opened valve used in suction line on multiple refrigerator installations which maintains evaporators in system at different temperatures.


Ultraviolet-Invisible radiation waves with frequencies shorter than wave lengths of visible light and longer than X-Ray.

Universal Motor-Electric motor which will operate on both AC and DC.

Urethane Foam-Type of insulation which is foamed in between inner and outer walls of display case.


Vacuum-Reduction in pressure below atmospheric pressure.

Vacuum Control Systems-In many automobile air conditioning systems, intake manifold vacuum is used to operate dampers and controls in system.

Vacuum Pump-Special high efficiency compressor used for creating high vacuums for testing or drying purposes.

Valve-Device used for controlling fluid flow.

Valve, Expansion-Type of refrigerant control which maintains pressure difference between high side and low side pressure in refrigerating mechanism. Valve is caused to operate by pressure in low or suction side. Often referred to as an automatic expansion valve or AEV.

Valve Plate-Part of compressor located between top of compressor body and head which contains compressor valves.

Valve, Service-Device used by service technicians to check pressures and charge refrigerating units.

Valve, Solenoid-Valve actuated by magnetic action by means of an electrically energized coil.

Valve, Suction-Valve in refrigeration compressor which allows vaporized refrigerant to enter cylinder from suction line and prevents its return.

Valves, Water-Most water cooling units are supplied with water valves. These valves provide a flow of water to cool the system while it is running. Most water valves are controlled by solenoids.

Vapor-Work usually used to denote vaporized refrigerant rather than the word gas.

Vapor Barrier-Thin plastic or metal foil sheet used in air conditioned structures to prevent water vapor from penetrating insulating material.

Vapor Charged-Lines and component parts of system which are charged at the factory.

Vapor Lock-Condition where liquid is trapped in line because of bend or improper installation which prevents the vapor from flowing.

Vapor Pressure-Pressure impassed by either a vapor or gas.

Vapor Pressure Curve-Graphic presentation of various pressures produced by refrigerant under various temperatures.

Vapor, Saturated-A vapor condition which will result in condensation into droplets of liquid as vapor temperature is reduced.

Variable Pitch Pulley-Pulley which can be adjusted to provide different pulley ratios.

V-Belt-Type of belt that is commonly used in refrigeration work. It has a contact surface which is in the shape of letter V.

V-Block-V-shaped groove in metal block used to hold shaft.

Velocimeter-Instrument used to measure air velocities using a direct reading air speed indicating dial.

Viscosity-Term used to describe resistance of flow of fluids.

Volatile Liquid-Liquid which evaporates at low temperature and pressure.

Voltage-Term used to indicate the electrical potential or electromotive force in an electrical circuit. It is voltage or electrical pressure which causes current to flow.

Voltage Control-It is necessary to provide some electrical circuits with uniform or constant voltage. Electronic deform or constant voltage. Electronic devices used for this purpose are called voltage controls.

Voltmeter-Instrument for measuring voltage action in electrical circuit.

Volumetric Efficiency-Term used to express the relationship between the actual performance of a compressor or of a vacuum pump and calculated performance of the pump based on its displacement versus its actual pumping ability.

Vortex Tube-Mechanism for cooling or refrigerating which accomplishes cooling effect by releasing compressed air through specially designed opening. Air expands in rapidly spiraling column of air which separates slow moving molecules (cool) from fast moving molecules (hot).

Vortex Tube Refrigeration-Refrigerating or cooling devices using principle of vortex tube, as in mining suits.

Walk-In Cooler-Large commercial refrigerated space kept below room temperature. Often found in large supermarkets or wholesale meat distribution centers.

Water-Cooled Condenser-Condensing unit which is cooled through use of water.

Water Defrosting-Use of water to melt ice and frost from evaporator during off-cycle.

Watt-Unit of electrical power.

Wax-Ingredient in many lubricating oils which may separate out if cooled sufficiently.

Wet Bulb-Device used in measurement of relative humidity. Evaporation of moisture lowers temperature of wet bulb compared to dry bulb temperature in same area.

Wet Cell Battery-Cell or connected group of cells that converts chemical energy into electrical energy by reversible chemical reactions.

Window Unit-commonly used when referring to air conditioners which are placed in a window. Normally a domestic application.

Wobble Plate-Swash Plate-Type of compressor designed by General Motors to compress gas, having pistons with piston motion parallel to crankshaft.

Woodruff Key-Device used to align and hold a flywheel, pulley or other rotating mechanism on a shaft, often halfmoon in shape.


Zero Ize-Trade name for dry ice. See Dry Ice.

source : www.mrair.com



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