HVAC/R Dictionary

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Words & Definitions for the letter A

Absolute Humidity: Amount of moisture in the air, indicated in grains per cu.ft³
Absolute Pressure: Gauge pressure plus atmospheric pressure(14.7 lb. per sq. in².)
Accessible Hermetic: Assembly of motor and compressor inside a single housing unit
Accumulator: Storage tank that receives liquid refrigerant from evaporator and prevents it from flowing into suction line before it changes to a vapor
ACR Tubing: Tubing used in air conditioning and refrigeration. Ends are sealed to keep tubing clean and dry
Air Conditioner: Device used to control temperature, humidity, and cleanliness of air in a conditioned space
Air Conditioning: Control of the temperature, humidity, air movement, and cleaning of air, in a confined space
Air-Cooled Condenser: Heat of compression is transferred from condensing coils to surrounding air
Air Diffuser: Grille designed to direct airflow in desired patterns
Air Handler: Fan-blower, heat transfer coil(evaporator), heater and housing
Algae: Low form of plant life found floating in condensate drain pans and lines
Alternating Current: Electric current in which direction of flow reverses or alternates. In the US 60-cycle(hertz) current direction reverses every 1/120th of second
Ambient Temperature: Temperature of fluid or air that surrounds an object on all sides
Ammeter: >Electric meter, calibrated in amperes, used to measure current
Amperage: Electron or current flow of one coulomb per second past a given point in circuit
Anemometer: Instrument for measuring the rate of airflow or motion
Anode: Positive terminal of electrolytic cell
Armature: Part of an electric motor, generator or other devise moved by magnetism
Aspect Ration: Ratio of length to width of rectangular air grille or duct
Aspirating Psychronometer: Device that draws sample of air through it in order to measure humidity
spiration: Movement produced in a fluid by suction
A.S.T.M. Standards: Standards issued by the American Society of Testing Materials
Atmospheric Pressure: Pressure that gasses exert on earth; measure in pounds per square in.²
Automatic Control: Valve action reached through self-operated means, not requiring manual adjustment
Automatic Defrost: System of removing ice and frost from evaporators automatically
Valve (AEV): Pressure-controlled valve that reduces high-pressure liquid refrigerant to low-pressure liquid refrigerant

Words & Definitions for the letter B

Back Pressure: Pressure in low side of refrigerant system, also called suction pressure or low side pressure
Back Seating: Seal the joint where the valve stem goes through the valve body. This is accomplished by design of the valve
Baffle: Plate or vane used to direct or control movement of air or fluid in one direction only
Ball Check Valve: Valve assembly designed to permit flow of fluid in one direction only
Barometer: Instrument for measuring atmospheric pressure
Bearing: Low friction device for supporting and aligning a moving part
Bleeding: Slowly reducing the pressure of liquid or gas from a system by slowly opening a valve
Boiling Point: Boiling temperature of a liquid under a pressure of 14.7 psia
Boiling Temperature: Temperature at which a fluid changes from a liquid to a gas
British Thermal Unit(Btu): Quantity of heat required to raise temperature of one lb. of water 1° F

Words & Definitions for the letter C

Capacitor: Type of electrical storage device used in starting and/or running circuits on many electric motors
Capacitor-Start-Motor: Motor which has a capacitor in the starting circuit
Capacity: Refrigeration rating system. Usually measured in Btu per hour or watts
Carbon Monoxide: Colorless, odorless and poisonous gas(CO) produced when carbon or carbonaceous fuels are burned with too little air
Cathode: Negative terminal of an electrical device. Electrons leave at this terminal
Cavitation: Localized gaseous condition that is found within a liquid system
Celsius Temperature Scale: Temperature scale used in the metric system. Freezing point of water is 0°; boiling point is 100°
Centimeter: Metric unit of linear measurement which equals .3937 inch
Change of State: Condition in which a substance changes from a solid to a liquid or a liquid to a gas caused by the addition of heat. The reversal is when a substance changes from a gas to a liquid, or a liquid to a solid, caused by the removal of heat
Check Valve: Device which permits fluid to flow in one direction only
Chill Factor: Calculated number based on temperature and wind velocity
Capillary Tube: Pertaining to or occurring in or as if in a tube of fine bore
Circuit: A system that includes all component parts to complete its designated function; beginning and continuing through the various components, returning to its original starting point
Circuit Breaker: Safety device which automatically opens an electrical circuit it overloaded
Comfort Zone: Area on psychometric chart which shows conditions of temperature, humidity and sometimes air movement in which most people are comfortable
Commutator: Part of rotor in electric motor which conveys electric current to rotor windings
Compression: Term used to denote increase of pressure on a fluid by using mechanical energy
Compressor: Pump of a refrigeration mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high-pressure or condensing side of the cycle
Compressor Displacement: Volume, in cubic inches, represented by the area of compressor piston head(s), multiplied by the length of the stroke
Compressor, Hermetic: Compressor in which the driving motor is sealed in the same dome or housing as the compressor
Compressor, Multiple Stage: Compressor having two or more compressive steps. Discharge from each step is the intake pressure of the next in series
Compressor, Reciprocating: Compressor which uses a piston and cylinder mechanism to provide pumping action
Condensate: A fluid formed when a gas is cooled to its liquid state
Condensate Pump: Device to remove water condensate that collects beneath an evaporator
Condensation: Liquid or droplets which form when a gas or vapor is cooled below its dew point
Condense: Action of changing a gas to a vapor
Condenser: The part of a refrigeration mechanism which received hot, high-pressure refrigerant gas from the compressor and cools gaseous refrigerant until it returns to a liquid state
Condenser Fan: Electric motor and fan blade used to move air through air-cooled condenser
Condensing Pressure: Pressure inside a condenser at which refrigerant vapor gives up it’s latent heat of vaporization and becomes a liquid. This varies with pressure
Condensing Unit: Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to move to the evaporator
Contaminant: Substance such as dirt, moisture or other matter foreign to refrigerant or refrigerant oil in the system
Control, Defrosting: Device to Automatically defrost evaporator. It may operate by means of a time clock
Control, Low-Pressure: Cycling device connected to the low-pressure side of system
Control, Motor: Temperature of pressure-operated devices used to control the running of motors
Control, Temperature: Temperature-operated thermostatic device which automatically opens or closes a circuit
Control Valve: Valve which regulates the flow or pressure of a median which affects a controlled process
Convection: Transfer of heat by means of movement or flow of a fluid or gas
Coulomb: The quantity of electricity transferred by an electric current of one ampere in one second
Current: Transfer of electrical energy in a conductor by means of electrons changing positions
Current Relay: A device which opens or closes a circuit. It is made to act by a change of current flow in that circuit
Cylinder Head: Plate or cap which encloses compression end of compressor cylinder
Cylinder, Refrigerant: Steel cylinder used to store and dispense refrigerant. The color code painted on the cylinder indicates which refrigerant the cylinder contains

Words & Definitions for the letter D

Damper: Device for controlling airflow
Defrost Cycle: Refrigerating cycle in which evaporator frost and ice accumulation is melted
Defrost Timer: Device connected into electrical circuit which shuts the unit off long enough to permit ice and frost accumulation on the evaporator to melt
Degree-Day: Unit that represents 1° degree of difference from inside temperature and the average outdoor temperature for one day
Delta Transformer: Three-phase electrical transformer which has ends of each of three windings electrically connected to form a triangle
Demand Meter: Instrument that measures the kilowatt-hour usage of a circuit or group of circuits
Design Pressure: Highest or most severe pressure expected during operation. Sometimes used as the calculated operating pressure plus an allowance for safety
Detector, Leak: Device used to detect and locate refrigerant leaks
Dew Point: Temperature at which vapor(at 100% humidity) begins to condense and deposit as a liquid
Diaphragm: Flexible material usually made of thin metal, rubber or plastic
Dichlorodifluoromethane: R-12, used in medium temperature applications
Diode: Two-element electron tube that allows more electron flow in one direction than the other
Direct Current (DC): Electron flow which continually moves in one direction only
Drier: Substance or device used to remove moisture from a refrigeration system
Drip Pan: Pan-shaped panel or trough used to collect condensate from the evaporator
Dry Bulb Temperature: Air temperature as indicated by an ordinary thermometer
Dry Cell Battery: Electrical device used to provide DC electricity, having no liquid in the cells
Dry Ice: Refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas(sublimates). It’s subliming temperature is -109° F. (-78°C)

Words & Definitions for the letter E

Eccentric: Circle or disk mounted off center on a shaft
Effective Area: The actual flow area of an air inlet or outlet. Gross area minus area of vanes or grille bars
Electrolysis: Movement of electricity through a substance which causes a chemical change in a substance or it’s container
Electromagnet: Coil of wire wound around a soft iron core. When electric current flows through the wire, the assembly becomes a magnet
Electron: Elementary particle or portion of an atom which carries a negative charge
Electronic Leak Detector: Electronic instrument which measure electronic flow across gas gap. Electronic flow changes indicate presence of refrigerant gas molecules
Evacuation: Removal of air(gas) and moisture from a refrigeration or air conditioning system
Evaporation: Term applied to the changing of a liquid to a gas. Heat is absorbed in this process
Evaporator: Part of a refrigeration mechanism in which the refrigerant vaporizes and absorbs heat
Evaporator Fan: Fan which increases airflow over the heat exchange surface of evaporators

Words & Definitions for the letter F

Fahrenheit Scale: On a Fahrenheit thermometer, under standard atmospheric pressure, boiling point of water is 212° and freezing pint is 32° above 0°
Female Thread: The internal thread on fittings, valves and machine bodies refrigerant
Freon: Trade name for a family of synthetic chemical refrigerants manufactured by E.I. du Pont de Nemours & Co., Inc
Fuse: Electrical safety device consisting of strip of fusible metal in circuit that melts when circuit is overloaded
Fusible Plug: Plug or fitting made with a metal of a know low-melting temperature. Used as a safety device to release pressures in case of fire

Words & Definitions for the letter G

Galvanic Action: The wasting away of two unlike metals due to electrical current passing between them. The action is increased in the presence of moisture
Gas Valve: Device in a pipeline for starting, stopping or regulating flow of gas
Gasket: Resilient(spongy) or flexible material used between mating surfaces of refrigeration unit parts, or on doors to give a leak proof seal
Gasket, Foam: Joint sealing material made of rubber or plastic foam strips
Gauge, Compound: Instrument for measuring pressures both above and below atmospheric pressures
Gauge, Manifold: Chamber device constructed to hold both compound and high pressure gauges. Valve control flow of fluids through it
Gauge, Port: Opening or connection provided for a service technician to install a gauge
Grain: A unit of weight and equal to 1/7000 lb. It is used to indicate the amount of moisture in the air
Ground, Short Circuit: Fault in an electrical circuit allowing electricity to flow into the metal parts of a mechanism
Ground Wire: Electrical wire which will safely conduct electricity from a structure into the ground

Words & Definitions for the letter H

Halide Torch: Type of torch used to safely detect halogen refrigerant leaks in system
Halogens: Substance containing fluorine, chlorine, bromine and iodine
Hanger: Device attached to walls or ceilings for support of pipelines
Head: Pressure usually expressed in feet of water, inches of mercury
Head, Static: Pressure of fluid expressed in terms of height of column of the fluid, such as water of mercury
Head Pressure: Pressure which exists in condensing side of refrigeration system
Head Pressure Control: Pressure-operated control which opens electrical circuit if the high-side pressure becomes too high
Header: Length of pipe or vessel to which two or more pipe lines are joined carries fluid from a common source to various points of use
Heat: Form of energy which acts on substances to raise their 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: The time it takes for heat to travel through a substance heated on one side
Heat Load: Amount of heat, measured in Btu or watts, which is removed during a period of 24 hours
Heat Pump: Compression cycle system used to supply heat to a temperature-controlled space. The same system can also remove heat from the same space
Heat Sink: Relatively cold surface capable of absorbing heat
Heat Transfer: The movement of heat from one body or substance to another. Heat maybe transferred by radiation, conduction, convection or a combination of these three methods
Heating Coil: Heat transfer device consisting of a coil of piping, which releases heat
Hertz(Hz): Correct terminology for cycles per second
Hg.(Mercury): Heavy silver-white metallic element; only metal that is liquid at ordinary room temperature
High Pressure Cut-Out: Electrical control switch operated by the high-side pressure which automatically opens electrical circuit if too high pressure is reached
High Side: Parts of a refrigerating system which are under condensing or high-side pressure
Horsepower: A unit of power equal to 33,000 ft-lbs. 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 into low pressure side
Hot Gas Defrost: Defrosting system in which hot refrigerant gas from the high side is directed through evaporator for short period of time in order to remove frost from evaporator
Humidity: Moisture. Dampness in air
Hydraulics: Branch of physics having to do with the mechanical properties of water and other liquids in motion
Hydrocarbons: Organic compounds containing only hydrogen and carbon atoms in various combinations
Hydrometer: Floating instrument used to measure specific gravity of a liquid
Hygrometer: Instrument used to measure degree of moisture in the atmosphere

Words & Definitions for the letter I

Idler: Pulley used on some belt drives to provide proper belt tension and to eliminate belt vibration
Ignition Transfer: Transformer designed to provide a high-voltage current. Used in many heating systems to ignite fuel, it provides a spark gap
Impedance: Opposition in an electrical circuit to the flow of an alternating current that is similar to the electrical resistance to a direct current
Impeller: Rotating part of the pump
Induction Motor: An AC motor which operates on the principle of a rotating magnetic field. The rotor has not electrical connection, but receives electrical energy by transformer action from field windings
Inductive Reactance: Electromagnetic induction in a circuit creates a counter or reverse(counter) emf(voltage) as the original current changes. It opposes the flow of alternating current
Inhibitor: Substance which prevents chemical reaction such as corrosion or oxidation
Ion: Group of atoms or an atom electrically charged

Words & Definitions for the letter J

Journal, Crankshaft: Part of shaft which contacts the bearing on the large end of the piston rod
Junction Box: Box or container housing group of electrical terminals

Words & Definitions for the letter K

Kilometer: Metric unit of linear measurement = 1000 meters
Kilowatt: Unit of electrical power, equal to 1000 watts

Words & Definitions for the letter L

Latent Heat: Heat energy absorbed in process of changing form of substance(melting, vaporization, fusion) without change in temperature or pressure
Latent Heat of Vaporization: Amount of heat, required per pound of a substance to change its state from a liquid to a vapor(gas)
Leak Detector: Device or instrument such as a halide torch, an electronic snifter; 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 Receiver: Cylinder (container) connected to condenser outlet for storage of liquid refrigerant in a system
Liter: Metric unit of volume which equals 61.03 cu. in³
Low Side: That portion of a refrigeration system which is below evaporating pressure
LP Fuel: Liquefied petroleum used as a fuel gas

Words & Definitions for the letter M

Male Thread: External thread on pipe, fittings and valves for making connections that screw together
Manometer: An instrument for measuring the pressure of gases and vapors. Gas pressure is balanced against column of liquid, such as mercury, in U-shaped tube
Mass: Quantity of matter held together so as to form one body
MBH: Thousands of British Thermal Units (82 MBH = 82,000 Btu)
Megohm: A unit of measure for electrical resistance. One megohm is equal to a million ohms
Megohmmeter: Instrument for measuring extremely high resistance’s (In the millions of ohms ranges)
Metric System: Decimal system of measuring
Micro: One millionth part of unit specified
Micrometer: Precision measuring instrument used for making accurate measurements to .001 to .0001 of an inch
Micron: Unit of length in metric system; a thousandth part (1/1000) of one millimeter
Milli: Combining form denoting one thousandth (1/1000); for example, millivolt means one thousandth of a volt
Modulating: Type of device or control which tends to adjust by increments (minute changes) rather than either “full on” or “full off” operation
Molecule: Smallest portion of an element or compound that retains chemical identity with the substance in mass
Monochlorodifluoremethane: Better know as Freon R-22. Cylinder color code is green (HVAC use)
Motor Capacitor: Single-phase induction motor with an auxiliary starting winding connected in series with a condensers (capacitor) for better starting characteristics
Motor Control: Device to start and/or stop a motor or hermetic motor compressor at certain temperature or pressure conditions
Motor Starter: High-capacity electric switches usually operated by electromagnets

Words & Definitions for the letter N

Neoprene: Synthetic rubber which is resistant to hydrocarbon oil and gas
Neutron: That part of the atom core which has no electrical potential; electrically neutral
Nominal Size Tubing: Tubing measurement which has an inside diameter the same as iron pipe of the same stated size
Nonferrous: Group of metals and metal alloys which contain no iron

Words & Definitions for the letter O

Ohm: A 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
Ohm’s Law: The mathematical relationship between voltage, current and resistance. Voltage = Amperes X Ohms
Oil, Refrigeration: Specially prepared oil used in refrigeration mechanisms which circulates with the refrigerant
Oil Separator: Device used to remove oil from gaseous refrigerant
Open Circuit: Interrupted electrical circuit which stops flow of electricity
Operating Pressure: The actual pressure at which the system works under normal conditions. This pressure may be positive or negative (vacuum)
Organic: Pertaining to or derived from living organisms
Orifice: Accurate size opening for controlling fluid flow
Oscilloscope: Fluorescent-coated tube which visually shows an electrical wave
Overload: Load greater than what the system or mechanism was intended
Overload Protector: Device, either temperature, pressure or current operated, which will stop operation of unit if dangerous conditions arise
Ozone: Bluish gaseous form of oxygen usually obtained by silent discharge of electricity in oxygen or air (0₃)

Words & Definitions for the letter P

Package Units: Complete refrigerating system including compressor, condenser and evaporator located in the refrigerated space
Packing: Sealing device consisting of soft material of one or more mating soft elements. Reshaped by manually adjustable compression to obtain or maintain a leak-proof seal
Piston: Close-fitting part of plug which moves up and down in a cylinder
Pitot Tube: Tube used to measure air velocities
Polyphase Motor: Electrical motor designed to be used with a three or four-phase electrical circuit
Potential Relay: Electrical switch which opens on high voltage and closes on low voltage
Potentiomenter: Instrument for measuring or controlling by sensing small changes in electrical resistance
Power Factor: Correction coefficient for the changing current and voltage values a-c power
PPM (Parts Per Million): Unit of concentration (for example, of solutions)
Pressure: The energy impact on a unit area; force or thrust on a surface.
Pressure, Gauge: Reading in pounds per in² above atmospheric
Pressure, Head: Force caused by the weight of a column or body of fluids. Expressed in feet, inches, or psi
Pressure, Suction: Pressure in the low-pressure side of a refrigeration system
Pressure Drop: The pressure difference at two ends of a circuit, or part of a circuit, the two sides of a filter
Pressure Gauge: An instrument for measuring the pressure exerted by the contents on its container
Pressure Regulator, Evaporator: Automatic pressure regulating valve mounted in suction line between the evaporator outlet and the compressor inlet. Maintain predetermined pressure and temperature in the evaporator
Pressure Switch: Switch operated by a rise or drop in pressure
Protector, Circuit: Electrical device which will open an electrical circuit if excessive electrical conditions occur
Proton: Particle of an atom with a positive charge
PSI: Symbol or initials used to indicate pressure measured in pounds per square in² absolute. Absolute pressure equals gauge pressure plus atmospheric pressure
PSIG: Symbols or initials used to indicate pressure in pounds per in² gauge. The “g” indicates that it is gauge pressure and not absolute pressure
Psychrometer or Wet: An instrument for measuring the relative humidity of atmospheric air. Bulb hygrometer
Psychrometric Chart: A chart that shows the relationship between the temperature pressure and moisture content of the air
Psychrometric Measurement: The measurement of temperature pressure and humidity, using a psychometric chart
Pump: Any one of the various machines which force a gas or liquid into — or draw it out of — something as by suction or pressure.
Pump, Down: The act of using a compressor or a pump to reduce the pressure in a container or a system.
Pump, Reciprocating: A pump having a reciprocating (moving up and down or back and forth) piston.
Pump, Screw: A pump having two interlocking screws rotating in housing.
Purging: Releasing compressed gas to the atmosphere through some part or parts for the purpose of removing contaminants from that part or parts. Normally Freon is the gas referred to. It is illegal to purge Freon to the atmosphere
Pyrometer: An instrument for measuring high temperatures.

Words & Definitions for the letter Q

There are currently no words with the letter Q in this dictionary.

Words & Definitions for the letter R

R-11: Trichloromonofluoromethane, a low pressure synthetic chemical refrigerant typically used in centrifugal chillers. (This refrigerant is no longer manufactured and was phased out as required by The Montreal Protocol)
R-12: Dichlorodifluoromethan, a medium temperature, used in maketables and some coolers
R-22: Monochlorodifluoromethane, low temperature, used in HVAC and occasionally coolers (The manufacture of new R22 will end in 2020 per The Montreal Protocol)
R-502: Azerotropic mixture of R-12 and R-115. This is a low temperature freezer and ice machine application
Radiant Heating: Heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned
Radiation: The transfer of heat by heat rays
Reciprocating: Back and forth motion of a straight line
Reed Value: Thin, flat tempered steel plate fastened at one end
Refrigerant: Substance used in a refrigeration mechanism. It absorbs heat in the evaporator by a change of state from a liquid to a gas and releases it’s heat in a condenser as the substance returns from the gaseous state back to a liquid state
Refrigerant Charge: Quantity of refrigerant in a system
Register: Combination grille and damper assembly covering an air opening or the end of an air duct
Relative Humidity: Ratio of (difference between) amount of water vapor present in air to greatest amount possible at same temperature
Relay: An electromagnetic mechanism moved by a small electrical current in a control circuit. It operates a valve or switch in an operating circuit
Relief Valve: A safety device on a sealed system. It opens to release fluids before dangerous pressure is reached
Remote System: Refrigerating system in which the condensing unit is separated, in a different location from the evaporator or air handler
Running Time: Amount of time a condensing unit is run per hour or per 24 hours
Running Winding: Electrical winding of motor which has current flowing through it during normal operation of the motor

Words & Definitions for the letter S

Saddle Valve: Valve body shaped so it may be silver brazed or clamped on to a refrigerant tubing surface
Saturation: Condition existing when substance contains all of another substance it can hold for that temperature and pressure
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
Seat: That portion of a valve mechanism against which the valve presses to effect shutoff
Second Law of Thermodynamics: Heat will flow only from material at higher temperature to material at lower temperature
Semi Conductor: A class of solids whose ability to conduct electricity lies between that of a conductor and that of an insulator
Semihermetic Compressor: Hermetic compressor with service valves
Sensible Heat: Heat which causes a change in the temperature of a substance
Separator, Oil: Device to separate refrigerant oil from refrigerant gas and return the oil to compressor crankcase
Service Valve: Manually operated valve mounted on refrigerating systems used for service operation
Short Cycling: Refrigerating system that starts and stops more frequently than it should
Shroud: The housing over the condenser unit. Also called a doghouse. Protects unit from weather
Sight Glass: The glass window in a refrigeration line. The normal color of a center dot is green. A yellow center indicates moisture in the system. Bubbles in the sight glass, after the unit has been operating for a time may indicate a low refrigerant charge
Silver Brazing: A brazing process containing some silver. Must be used in refrigeration brazing
Single Phase Motor: Electric motor which operates on single phase alternating current
Sling Psychrometer: Measuring device with wet and dry bulb thermometers. Moved rapidly through air it measures humidity
Slugging: A condition in which a mass of liquid enters the compressor causing hammering. This breaks valves and washes lubricant out of bearings
Solenoid Valve: An electromagnet with a moving core. It serves as a valve or operates a valve
Specific Gravity: Weight of a liquid compared to water which is assigned value of 1.0
Splash System, Oiling: Method of lubricating moving parts by agitating or splashing oil in the crankcase
Split-Phase Motor: A motor with two starter windings. Both windings are in use while starting. One is disconnected by a centrifugal switch after the motor attains speed. The motor then operates on one winding
Split System: A refrigeration or air conditioning installation that places the condensing unit outside or away from the evaporator. This also applies to heat pumps
Squirrel Cage: Fan which has blades parallel to a fan axis and moves air at right angles or perpendicular to the fan axis
Standard Atmosphere: Condition when air is at 14.7 psia pressure, at 68° F temperature and relative humidity of 36%
Standard Conditions: Used as a basis for air conditioning calculations; temperature of 68 F, pressure of 29.92 and relative humidity of 30%
Starting Relay: Electrical device which connects and/or disconnects the starting winding of an electric motor
Starting Winding: Winding in an electric motor used only briefly while the motor is starting
Starter Motor: Stationary part of an electric motor
Subcooling: Cooling of liquid refrigerant below it’s condensing temperature
Sublimation: Condition where a substance changes from a solid to a gas without becoming a liquid
Suction Line: Pipe used to carry refrigeration gas from the evaporator to the condenser
Suction Pressure Control Valve: Device located in the suction line which maintains constant pressure in the evaporator during the running portion of cycle
Suction Service Valve: A two-way manually operated valve located at the inlet to the compressor. It controls suction gas flow and is used to service the unit
Suction Side: Low-pressure side of the system extending from the refrigerant control through the evaporator to the inlet valve of the compressor
Superheat: 1: Temperature of vapor above its boiling temperature as a liquid at that pressure. 2: The difference between the temperature at the evaporator outlet and the lower temperature of the refrigerant evaporating in the evaporator

Words & Definitions for the letter T

Temperature-Humidity Index: Actual temperature and humidity of air sample compared to air at standard conditions
Test Light: Light provided with test leads. Used to test or probe electrical circuits to determine if they have electricity
Therm: Quantity of heat equal to 100,000 Btu
Thermal Relay: Heat-operated electrical control used to open or close a refrigeration system electrical circuit. This system uses a resistance wire to convert electrical energy into heat energy
Thermistor: Basically a semiconductor which has electrical resistance that varies with temperature
Thermocouple: Device which generates electricity, using the principle that if two unlike metals are welded together and a junction is heated, a voltage will develop across the open ends
Thermodynamics: Part of science which deals with the relationship between heat and mechanical action
Thermostat: Device which senses ambient temperature conditions and in turn, acts to control a circuit
Thermostatic Expansion Valve: Control valve operated by temperature and pressure within the evaporator. It controls the flow of refrigerant. The control bulb is attached to outlet of evaporator
Three-Phase: Operating by means of combination of three alternating current circuits which differ in phase by 1/3 of a cycle
Three-Way Valve: Multi-orifice (opening) flow control valve with three fluid flow openings
Ton of Refrigeration: Refrigerating effect equal to the melting of 1 ton of ice in 24 hours. This may be expressed as follows: 288,000 Btu/24 hr., 12,000 Btu/1 hr, 200 Btu/min
Torque: Turning or twisting force
Torque, Starting: Amount of torque available, when at 0 speed to start and accelerate the load
Total Heat: Sum of both the sensible and latent heat
Transducer: Device turned on by charge of power from one source for purposes of supplying power in another form to second system
Transformer: Electromagnetic device which transfers electrical energy from primary circuit into variations of voltage in secondary circuit
Transistor: Electronic device commonly used for amplification, similar in use to an electron tube. Depends on conduction properties of semiconductors in which electrons moving in one direction are considered as leaving holes that serves as carriers of positive electricity in opposite direction
Two-Way Valve: Valve with one inlet port and one outlet port

Words & Definitions for the letter U

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 either a-c or d-c

Words & Definitions for the letter V

Vacuum: Pressure lower than atmospheric pressure
Vacuum Pump: Special high efficiency device used for creating high vacuums for testing or drying purposes
Valve Expansion: A type of refrigerant control that maintains constant pressure in the low side of a refrigeration mechanism. Valve is caused to operate by pressure in the low or suction side. Often referred to as an automatic expansion valve or AEV
Valve Service: A device used to check pressures, service and charge refrigerating systems
Valve Solenoid: Valve made to work by magnetic action through an electrically energized coil
Valve Suction: Valve in refrigeration compressor which allows vaporized refrigerant to enter cylinder from suction line and prevent its return
Valve Plate: Part of compressor located between top of compressor body and the head. It contains compressor valves and ports
Vapor Saturated: Vapor condition that will result in condensation into droplets of liquid if vapor temperature is reduced
Vapor Lock: Condition where liquid is trapped in line because of bend or improper installation. Such vapor prevents liquid flow
Vapor Pressure: Pressure imposed by either a vapor or gas
Vaporization: Change of liquid into a gaseous state
Variable Pitch Pulley: A pulley which can be adjusted to provide different pulley drive ratios
V-belt: A type of belt commonly used in refrigeration work. It has a contact surface with the pulley that is in shape of letter V
Vibration Eliminators: Soft or flexible substance or device which will reduce the transmission of a vibration
Voltage: 1-Term used to indicate the electrical potential or electromotive force in an electrical circuit. 2-Voltage or electrical pressure which causes current to flow. 3-Electromotive force
Voltmeter: Instrument for measuring voltage 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

Words & Definitions for the letter W

Watt: Unit of electrical power
Wet Bulb Temperature: The measure of the degree of moisture. It is the temperature of evaporation for an air sample

Words & Definitions for the letter X

There are currently no words with the letter X in this dictionary.

Words & Definitions for the letter Y

There are currently no words with the letter X in this dictionary.

Words & Definitions for the letter Z

There are currently no words with the letter X in this dictionary.