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HVAC/R Dictionary

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.