Absolute Humidity - Is the amount of humidity in the air, indicated by grains

Absolute Pressure - is the sum of gauge and atmospheric pressure (psia). 

Absolute Temperature - Is temperature measured on the Kelvin scale

Absolute Zero - The lowest temperature theoretically attainable on the Kelvin scale . Approximately  -273.16 o C

Absolute humidity - The humidity of the air measured buy the number of grains of water vapor present in one cubic meter of air. 

Absorbent - A substance with the ability to absorb another substance.

Absorption-  i n physics, the taking up of light, heat, or other  energy by molecules. The absorbed energy is converted into heat;  Absorption in chemistry is the taking up of one substance by another. For example, a gas such as oxygen may be absorbed, or dissolved, in water. In the HVAC industry we absorbed heat energy from the medium being cooled and transfer that energy in the refrigerant.

Active Cooling - Compressor driven air-conditioning.

Accumulator - A shell device installed in the suction line of a HVAC system to prevent liquids from entering the compressor.

Acrolein - An Agent added to methyl chloride, to make you aware of refrigerant leaks.

Activated Alumina - a type of aluminum oxide that absorbs moisture. (used in refrigerant driers).

Activated Carbon - A processed carbon used in filter driers, commonly used in air filters to clean the air.

Adiabatic - A change in gas condition where no heat is added or removed except in the form of work.

Adsorption- Adsorption, which is often confused with absorption, refers to the adhering of molecules of gases and liquids to the surfaces of porous solids. Adsorption is a surface phenomenon; absorption is an intermingling or interpenetration of two substances.

Air Balance- To distribute air through a system to precisely match the required amount.

Air Conditioner - A device used to control temperature and humidity of the air.

Air Conditioning - To condition air,   transfer of heat and humidity from one medium to an other . 

Air Handler - A fan-blower , heat transfer coil and housing parts of a system.

Air, Standard - Air having a temperature of 68 o F (20 o C), a relative humidity of 36% at 14.7 psia.

Air Infiltration - The unwanted entrance of air due to suck things as leakage, temperature difference or wind.

Air vent - A valve , either manual or automatic that is used to remove unwanted air from the highest point of a piping system.

Air to Air -  both the condensing and evaporating mediums are air.

Alcohol Brine - Water and alcohol solution witch remains a liquid below 32 o F.

Alternating Current - electrical current that reverses direction periodically. 

Ambient temperature - The temperature surrounding an object.

Ammeter - An Instrument for measuring the current in amps, milliamps or micro amps.

Ampere - the current required to produce a certain amount of force between two wires. 

Amplitude - The highest value reaches by voltage,  current or power during a complete cycle.

Analogue - A system in which data is represented as a continuously varying voltage.

Anemometer- an instrument that measures air speed.

Anticipation - to realize in advance, ie- a heat anticipator on a thermostat is used to shut down a furnace prior to the set point, as we are anticipating that the furnace will continue to run until the heat exchange is cooled and we will be at set point buy that time .

Anode - Positive terminal of electrolytic cell.

ASHRAE - American Society of Heating Refrigeration and Air Conditioning Engineers.

Aspect Ratio - The ratio of length to width of a rectangular air grill or duct.

Aspiration - The movement is a fluid produced by suction.

Atmospheric Pressure - Is the pressure that the atmosphere exerts on us. At sea level the is 14.7 psig also written as 29.92 " Hg.

Atmospheric Condenser - A condenser operated with water that is exposed to the atmosphere.

Atmospheric Dust Spot Efficiency - the measurement of a devices ability to remove dust from the air.

Automatic Expansion Valve - A pressure actuated metering device to regulate the flow of refrigerant into the evaporator according to the evaporator pressure.

Azeotropes -  refrigerants that are mixtures or blends of different refrigerants that are at the same ratio in vapor as well as in liquid state.

Azeotropes - (Near) - A zeotrope having a temperature glide sufficiently small that it is inconsequential.

Azeotropic mixture - is a combination of different refrigerants to mask one with desirable refrigerant properties, an example of this is R-502 witch is a mixture of 48.8% R-22 and 51.2% R-115.

Back EMF - The emf that opposes the normal flow of current in a circuit.

Back Pressure - This is the refrigerant pressure in the low side of the system also called low side pressure or suction pressure.

Baffle - A device used to divert the flow of a substance (air or liquid).

Balanced Pressure - when the both the inside and outside pressure of a container equal each other.

Barometer- is used to measure atmospheric pressure.

Barometric Damper - Also called draft damper, is a device installed in a chimney to allow for the adjustment of dilution air.

Bearing - mechanical device for decreasing friction in a machine in which a moving part bears—that is, slides or rolls while exerting force—on another part. Usually in a bearing the support must allow the moving part one type of motion, for example, rotation, while preventing it from moving in any other way, for example, sidewise. The commonest bearings are found at the rigid supports of rotating shafts where friction is the greatest.

Bellows - A corrugated cylindrical container which moves with a pressure change.

Belt - A rubber like, continuous loop placed between two or more pulleys to transfer a rotary motion.

Bernoulli's Theorem - In stream of liquid, the sum of elevation head, head pressure, and velocity remains constant along any line of flow, provided no work is done by or upon liquid on course of its flow ; decreases in portion to energy lost in flow.

Bimetal - A temperature regulating or indicating device which works on the principal that two dissimilar metals with unequal expansion rates, welded together and will bend as their temperature changes.

Blast Freezer - A low -temperature evaporator that uses a fan to force air rapidly over a evaporator surface.

Bleed-Valve - A valve with a small opening witch permits a minimum fluid flow when the valve is closed.

Blend - A mixture consisting of two or more single components.

Blower - similar to a fan used to push air 

Boiler - device for heating water or generating steam above atmospheric pressure. 

Boiling Point- The point at witch a substance will vaporize if anymore heat is added.

Boiling temperature - Temperature at witch a fluid changes from a liquid to a gas.

Booster - A term used for the first stage compressor in a cascading system.

Bore - The inside diameter of a cylinder.

Boyle's Law - Boyle's law states that the volume of a given amount of gas varies inversely with its pressure, if temperature is constant. This means that at a constant temperature, the pressure of a gas will increase as the volume of the gas is decreased. 

Brazing - a method of joining two metal surfaces by using nonferrous filler metal heated to above 430° C (800° F), but below the melting point of the metals to be joined.

BTU - British Thermal Unit - The amount of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit.

Bridge rectifier - A full-wave rectifier in which there are four arms - each containing a diode.

Brine - A salt water mixture commonly used as a secondary refrigerant.

Burner - A device in which the burning of fuel takes place.

Bypass - The passage at one side of or around a regular passage.

Calcium Sulfate - is used as a drying agent or desiccant in the liquid line driers.

Calibrate – To determine accurate measurements and reset instrument to these settings.

Calibration - To correct any error an interment reads

Calorie - the amount of heat ( by weight) that is required to raise the temperature of water 1 degree Celsius.

Calorimeter - Device used to measure the quantities of heat.

Cam - Mechanical component that is oblong, giving a reciprocating mo­tion when rotated.

Capacitance - ability of a circuit system to store electricity. The capacitance of a capacitor is measured in farads and is determined by the formula C = q/V, where q is the charge (in coulombs) on one of the conductors and V is the potential difference (in volts) between the conductors. The capacitance depends only on the thickness, area, and composition of the capacitor's dielectric.

Capacitor- device for storing an electrical charge

Capacitive Reactance - The opposition to alternating current as a result of capacitance; expressed in ohms.

Capacitor-Start Motor - A motor that requires a capacitor in the start­ing circuit.

Capacity- The amount of heat energy that a HVAC system can add or removed from a medium .

Capillary Tube - a metering device that uses it's internal diameter, length and pressure drop to determine it's capacity and has a fixed regulation.

Carbon Dioxide - Compound of carbon and oxygen, is sometimes used in refrigerants

Carbon Filter - Air filter housing activated carbon.

Carbon Monoxide - Colorless, odorless, and poisonous gas pro­duced when carbon or carbonaceous fuels incorrectly burnt.

Carbon Tetrachloride - a chemical used as a solvent for removing grease oil and sludge.

Cascade System - Arrangement in which two or more refrigerating systems are used in series.

Cathode - Negative terminal of an electrical device.

Cavitation - Localized gaseous condition that is found within a liquid stream.

Celsius Temperature Scale - Temperature scale used in metric system.

Centimeter - Metric unit of linear measurement.

Centrifugal Compressor - A compressor employing centrifugal force for compression.

Centralized Computerized Controller - Energy control device, centrally located, which makes control decisions based on operating data, programmed information, and stored data.

Central Station - Central location of condensing unit with either wet or air-cooled condenser. Evaporator located as needed and connected to the central condensing unit.

CFC - Cloro- Floro Carbon

CFM - Cubic feet per minute.

Charge - The amount of refrigerant in a system.

Change of State - the point at witch a substance changes from a solid to a liquid or a liquid to a gas due to addition of heat. Or, the reverse, in which a substance changes from a gas to a liquid, or a liquid to a solid, due to removal of heat.

Charles' Law - Volume of a given mass of gas at a constant pressure varies according to its temperature.

Change of State - To change from one state to another ie. liquid to vapor.

Charging - to add a charge of refrigerant to a system.

Check Valve - A check valve is a mechanical device normally applied to a piping system which allows fluid to flow in only one direction.

Chiller - A cooling system used to cool water or brine.

Chemical Refrigeration - System of cooling using a disposable refrigerant.

Chill Factor - Calculated number based on temperature and wind velocity.

Chimney - Vertical shaft for carrying flue gases to the outside atmosphere.

Chimney Connector – A pipe connecting the heating appliance with the chimney.

Chimney Effect - Tendency of air or gas to rise when heated.

Chimney Flue - The passageway in a chimney.

Choke Tube - Throttling device used to maintain correct pressure dif­ference between high side and low side in refrigerating mechanism.

Circuit - Tubing, piping, or electrical wire installation which permits continuous flow.

Circuit, Parallel - Arrangement of electrical devices in which the cur­rent divides and travels through two or more paths.

Circuit, Pilot - Secondary circuit used to control a device in the main circuit.

Circuit, Series - Electrical path in which elec­tricity to operate second lamp or device must pass through first; cur­rent flow travels, in turn, through all devices connected together.

Circuit Breaker - Safety device, which automatically opens an electrical circuit if overloaded.

Closed Circuit - Electrical circuit in which electrons are flowing.

Closed Loop - Any piping system where the internal fluids are sealed from their surroundings. Commonly  referred to as glycol loops 

Clutch, Magnetic - Clutch built into automobile compressor flywheel, operated magnetically, which allows pulley to revolve without driving compressor .

Coefficient of Conductivity - Measure of the relative rate at which different materials conduct heat.

Coefficient of Expansion - Increase in unit length, area, or volume for one degree rise in temperature.

Coefficient of Performance (COP) - System capacity divided by electrical energy consumed.

Cogeneration - Primary source of energy that is also used to produce a secondary source of energy.

Coil Refrigeration- Any cooling element made of piping .

Coil Electrical - A conductor wound in a series of turns.

Cold - The absence of heat.

Cold Storage - The process of preserving perishable items on a large scale.

Cold Wall - Refrigerator construction which has the refrigerator serving as the cooling surface.

Colloids - Miniature cells peculiar to meats, fish, and poultry which disrupted, cause food to become rancid. Low temperatures minimize this action.

Combustible Liquids - Liquid having a flash point at or above 140 o F

Comfort Chart - A psychometric chart for the propose of showing effective temperatures.

Comfort Zone - Area on psychometric chart which shows condition of temperature, humidity in which people are comfortable.

Compound Compressor- A compressor with one ore more head.

Compound Gauge - Instrument for measuring pressure both above and below atmospheric pressure.

Compound Refrigerating Systems - System, which has several compressors or compressor cylinders in series.

Compression - Term used to denote increase of pressure on a fluid using mechanical energy.

Compression Gauge - An instrument used to measure positive pressure.

Compressor -  A refrigeration component that make a pressure difference in the system witch causes refrigerant to flow.

Compressor Reciprocating - Compressor which uses a piss cylinder mechanism to provide pumping action.

Compressor, Rotary - Compressor which uses vanes, a mechanisms, or other rotating devices to provide pumping action.

Condensate - A fluid formed when a gas is cooled .

Condensation - Liquid or droplets which form when a gas or cooled below its dew point.

Condense - The changing of a gas or vapor to a liquid.

Condenser - The heat rejection component of a system  where the refrigerant is condensed from a vapor to liquid. 

Condenser, Air Cooled - Heat exchanger that transfers heat to the surrounding air.

Condenser, Water Cooled - Heat exchanger that transfers heat to water.

Condense Comb - Comb-like device used to straighten the metal fins on condensers or evaporators.

Condenser Fan - A fan used to move air through air-cooled condenser.

Condensing Furnace - A high efficiency furnace that also removes latent heat form the combustion products.

Condensing Pressure - See head pressure

Condensing temperature – the temperature at witch a substance will condense.

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 the metering device.

Conductivity- the ability of as material to transfer heat.

Conduction - the passage of heat from one point to another by transition of molecular energy from particle to particle through a conductor.

Conductor - Substance or body capable of transmitting electricity or heat.

Constrictor - Tube or orifice used to restrict flow of a gas or a liquid.

Contaminant - Substance such as dirt, moisture, or other matter foreign to refrigerant or refrigerant oil in system.

Control - any device to to start stop regulate or protect a system.

Control, Low Pressure - a Safety device connected to low-pressure side of system.

Control, Refrigerant - A device used to regulate flow of liquid refrigerant into evaporator.

Control, Temperature - Temperature-operated thermostatic device which automatically opens or closes a circuit.

Control System - All of the components required for the automatic control of a process variable.

Control Valve - Valve which regulates the flow or pressure of a medium which affects a controlled process.

Controller - A group of controls and circuits used to accurately and automatically operate a device.

Convection - Transfer of heat from one point to another by means of gravity.

Convection, Forced - Transfer of heat resulting from forced move­ment of liquid or gas by means of a fan or pump.

Convection, Natural - Circulation of a gas or liquid due to difference in density resulting from temperature differences.

Cooler - Heat exchanger which removes heat from a substance.

Cooling Tower - Device which cools by water evaporation in air

Copper Plating - Abnormal condition developing in some units in which copper is electrolytically deposited on some compressor surfaces.

Core, Air - Coil of wire not having a metal core.

Core, Magnetic - Magnetic center of a magnetic field.

Corrosion - Deterioration of materials from chemical action.

Coulomb - The quantity of electricity transferred by an electric current of one ampere in one second.

Counter EMF - Tendency for reverse electrical flow as magnetic field changes in an induction coil.

Counter Flow - Flow in opposite direction.

Couplings - Mechanical device joining refrigerant lines.

Crankshaft Seal - Leak proof joint between crankshaft and compressor body.

Crisper - Drawer or compartment in refrigerator designed to provide high humidity along with low temperature to keep vegetables especially leafy vegetables-cold and crisp.

Critical Pressure - Compressed condition of refrigerant, which gives liquid and gas the same properties.

Critical Temperature - Temperature at which vapor and liquid have same properties.

Critical Vibration - Vibration which is noticeable and harmful to structure.

Cross Charged- Two fluids which together create a desired pressure-temperature properties.

Cryogenics -Refrigeration which deals with producing temperatures of 250 0 F below zero and lower.

Current - the flow of electrons through a conductor.

Current Relay - Device which opens or closes a circuit upon a change in current flow.

Cupro-nickel - 90% copper / 10% nickel alloy which has high corrosion resistance to water containing salt, sulphur, chlorides and other dissolved minerals.

Cut –In - The value at which the con­trol circuit closes.

Cut-Out - The value at which the control cir­cuit opens.

Cycle - Series of events or operations which have tendency to repeat in the same order.

Cylinder, Refrigerant - A cylinder used to store refrigerant.

Cylinder Head - Plate or cap which encloses compression end of com­pressor cylinder.

Dalton's Law - Vapor pressure created in a container by a mixture of gases is equal to sum of individual vapor pressures of the gases con­tained in mixture.

Damper - A device used to regulate to flow of air.

Deaeration - Act of separating air from fluids.

Decibel - Unit used for measuring relative loudness of sounds.

Defrost - The process of removing ice from a unit.

Defrost Cycle - Refrigerating cycle in which evaporator frost and is melted.

Defrost Timer – A device which shuts unit off the compressor long enough to permit ice and frost accumulation on evaporator to melt.

Defrosting - See defrost

Degreasing - Solution or solvent used to remove grease from equipment.

Degree Day - The number of degrees that the mean temperature for that day is below 65° F.

Dehumidify - the process of removing moisture from the air.

Dehumidifier - Device used to remove moisture from air.

Dehydrator - A device used to dry refrigerant.

Dehydrator –Receiver – A liquid refrigerant receiver that also contains a desiccant to remove moisture.

Deice Control - Device for operating a refrigerating system in such a way as to provide melting of the accumulated ice and frost.

Delta Transformer - Three-phase electrical transformer wired in the delta configuration, this is also forms a triangle.

Demand Meter - A instrument that measures the kilowatt-hour usage of a circuit.

Density - The mass per unit volume.

Deodorizer - A device that absorbs odors, usually by principle of apsorption.

Design Pressure - Highest or most severe pressure expected during operation.

Desiccant - A substance used to remove moisture from refrigerant.

Desuperheater - A heat exchanger designed to remove excess superheat from a system. Normally used as a heater for pools or domestic water.

Dew - Condensed atmospheric moisture deposited in small drops on cool surfaces.

Dew Point -: Temperature at which begins to condense .

Diac - A two-lead alternating current semiconductor that allows current to flow in both directions at a preset voltage.

Diaphragm – Now get your mind out of the gutter J now that your awake it's A flexible material usually made of thin metal, rubber, or plastic.

Die Casting - Process of molding low-melting-temperature metals in ac­curately shaped metal molds.

Dielectric Fluid - Fluid with high electrical resistance.

Dilution Air - is air that is mixed with the products of combustion prior to them exiting the vent.

Diode- a electrical component that will only allow current to pass in one direction.

Differential - The difference between the cut-in and cut-out of a control.

Direct Current - Current that travels only in one direction. 

Direct Digital Control (DDC) - Use of a digital computer to perform required automatic control operations.

Direct Expansion  -  When the refrigerant is the system is either condensed or evaporated directly by the medium being heated or cooled.

Displacement - Volume obtained by multiplying area of cylinder bore by length of piston stroke.

Distilling Apparatus - Fluid-reclaiming device used to reclaim used refrigerants.

Distribution Controls - Systems which help evenly and efficiently transfer the heating or cooling medium to the area where it is needed.

District Heating and Cooling - Use of a central utility system de­signed to provide heating and cooling to large residential and industrial areas.

Dome-Hat - Sealed metal container for the motor compressor of a refrigerating unit.

Double Duty Case - Commercial refrigerator in which a part of space is for refrigerated storage and part is equipped with glass windows for display purposes.

Draft - A heating term used to ensure the escape of flue gases and aid combustion.

Draft Gauge - An Instrument used to measure the draft in an apalince.

Draft Regulator - Device which maintains a desired draft in a combustion-heated appliance by automatically controlling the chimney draft to the desired value.

Drip Pan - Pan-shaped panel or trough used to collect condensate from evaporator.

Drier- same as dehydrator.

Dry Bulb Temperature - The actual temperature as recorder on a standard thermometer.

Dry Capacitor Condenser - Electrical device made of dry metal and dry insulation; used to store an electrical charge.

Dry Cell Battery - A battery, having no liquid in the cell.

Dry Ice - Refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas (sublimates).

Dry System - Refrigeration system which has the evaporator liquid refrigerant mainly in the atomized or droplet condition.

Duct- a device used to distribute air.

Dynamometer - A device for measuring power input or output of a mechanism.

Ebullator - A device inserted in a flooded evaporator tubes to prevent the evaporator from becoming oil bound.

Eccentric – Is a disk mounted off center on a shaft. 

Eddy Currents - Induced currents flowing in a core. 

EER - See ENERGY EFFICIENCY RATIO. 

Effective Area - Actual flow area of an air inlet or outlet. 

Effective Temperature - Overall effect on a human of air temperature, humidity, and air movement. 

Efficiency - Output of a device, system, or activity, divided by the in­put necessary to create the output. 

Ejector - A device which uses high fluid velocity, such as a venturi, to create low pressure or vacuum at its throat to draw in fluid from another source.

Electric Defrosting - Use of electric resistance heating coils to melt ice off evaporators. 

Electric Heating – Heating using electric resistance heaters. 

Electrodepositing Process - Process in which metallic particles are applied to another metal surface through the use of an electric current.

Electrolysis - Movement of electricity through a substance which causes a chemical change in the substance or its container.

Electromagnet – A coil of wire wrapped an iron core. When electric current flows through wire, the assembly becomes a magnet.

Electromagnetic Energy - Energy that has both electrical and magnetic characteristics.

Electron - The portion of an atom that carries a negative charge.

Electronic Control Diagnostics - Trouble codes that may be referenced on an automatic climate control system to diagnose problems.

Electronic Leak Detector – A electronic instrument that measures electronic flow across gas gap. Electronic flow changes indicate presence of refrigerant gas molecules.

Electronic Relay – A relay that is mounted on a circuit board and is controlled by a electronic signal , such as a triac, 

Electronic Sight Glass – A electronic device that detects the presence of vapor in the liquid. 

Electronic Thermistor – A temperature sensitive resistor used on electronic thermostats. 

Electronic Thermostat – A thermostat that uses electronic components to accomplish various sensing, switching, timing, staging,and display functions. 

Electronics - Field of science dealing with electron devices and their uses. 

Electrostatic Filter - A filter for cleaning air that utilizes electricity to attract dust particles to electrically charged plates. 

EMF - Electromotive force. Symbol : E. Unit : volt. Its the property of electrical energy that causes current to flow.

Emitter - The lead of a transistor shown using an arrow with a head on it. 

End Bell – the plates on the ends of a electric motor which usually holds motor bearings. 

End Play - The movement of the motors shaft along its centerline. 

Endothermal - Chemical reaction in which heat is absorbed. 

Energy - The ability to do work. 

Energy Audit - To accurately determining the current energy consumption for a given area. 

Energy conservation – To look for, determine and institute changes that will conserve energy.

Energy Efficiency Ratio (EER) - Cooling capacity in BTU/hr divided by electrical energy consumed in watts.

Energy Management Control System - A system that optimizes total energy usage in a building.

Energy Utilization Index (EUI) - A number which is used to com­pare energy usages for different areas. It is calculated by dividing the energy consumption (in Btus) by the square footage of the condition­ed area.

Enthalpy - Total amount of heat in one pound of a substance.Entropy - Mathematical factor used in engineering calculations. Energy in a system.

Environment - The surrounding conditions.

Enzyme - Organic substance, that speeds up chemical changes in foods. 

Eutectic - That certain mixture of two substances providing lowest melting temperature of all the various mixes of the two substances.

Eutectic Point - Freezing temperature for eutectic solutions. 

Evacuation – The removal of contaminants in a refrigeration system.

Evaporator - The heat absorption component of a system  where the refrigerant is evaporated from a liquid to a vapor. 

Evaporator, Dry Type - Evaporator in which the refrigerant is in the liquid droplet form. 

Evaporator, Flooded - Evaporator containing liquid refrigerant at all times. 

Evaporator Fan - A mechanical device that increases airflow over the heat exchange surface of evaporators.

Evaporative Condenser - is one that utilizes the evaporation of water by air at the condenser surface as a means of heat dissipation.

Evaporation - Is the change of state from a liquid to a vapour.

EWT - Entering water or fluid temperature.

Exfiltration - Slow flow of air from the building to the outdoors.

Exhaust Port - That opening which carries the fluid to the downstream pressure of a fluid system.

Exhaust Valve - A movable port which provides an outlet for the cylinder gases in a compressor. 

Exothermal - A chemical reaction in which heat is released.

Expansion Joint - A device designed to allow movement caused by expansion and contraction.

Expansion Valve – Is one type of metering device in refrigerating system, which reduces the pressure from the high side to the low side and is operated by pressure.

 Expendable Refrigerant System – A system which discards the refrigerant after it has evaporated.

 External Drive - A Term used to indicate a compressor driven directly from the shaft or by a belt using an external motor.

 External Equalizer - Tube connected to the outlet of the evaporator to allow the diaphragm of the thermostatic expansion valve to disregard any pressure drop in the evaporator.

Fahrenheit Scale – The scale at witch , under standard at­mospheric pressure, the boiling point of water is 212 degrees and freez­ing point is 32 degrees.

Fail Safe Control – A device that fails in the open or safe position if and when it ceases to operate.

Fan - Radial or axial flow device used for moving or producing flow of gases.

Farad - Unit of electrical capacity; used to value capacitors.

Faraday Experiment - Silver chloride absorbs ammonia when cool and releases it when heated.

Fast Food Freezing – A freezing method that uses liquid nitrogen or carbon diox­ide to turn fresh food into long lasting frozen food.

Feedback - Information on current operation of a system or device used by the control system to modify future operation.

Feedback Control System – A control system that is constantly cor­recting the condition.

Female Thread – On fittings these are the internal threads.

Field Pole - Part of the stator of a motor which concentrates magnetic field of field winding.

Filter - is used to remove solid material from a gas or liquid buy means of straining.

Fire Damper - A damper installed in a duct system that is normally open , upon the breakage of a heat sensitive link the damper will close.  

Flammability - The ability for a material to burn.

Flammable Liquids - Liquids having a flash point below 140 0 F (60 0 C) and a vapor pressure not exceeding 40 psia (276 kPa) at 1OO 0 F (35 0 C).

Flapper Valve - Thin metal valve used in refrigeration compressors which allows gaseous refrigerants to flow in only one direction.

Flare - A soft tubing connector commonly used to connect soft copper piping

Flash Gas - The gas resulting from the instantaneous evaporation of the refrigerant when it's pressure is lowered. 

Flash point- Temperature at which flammable liquid will give of suffi­cient vapor to support a flash flame but will not support continuous combustion.

Flash Weld – A resistance type weld in which mating parts are brought together under considerable pressure while a heavy electrical current is passed through the joint to be welded.

Flexible Duct - A duct that can be routed around obstacles by bending it gradually.

Float Valve - A valve that controls the level of a fluid by the means of the sensing element floating in the fluid.

Flooded System - A refrigerating system in which liquid refrigerant fills most of the evaporator.

Flooded System, High-Side Float - Refrigeration system which has a float operated by the rate of the high-side liquid refrigerant being condensed.

Flooded System, Low-Side Float - Refrigeration system which has a float operated by the rate of evaporation of liquid refrigerant from the evaporator.

Flooding – The allowing a liquid to flow into a part of a system.

Flow Check Piston – A metering device that has a piston assembly, with an orifice in the center.

Flow Meter – An instrument used to measure velocity of fluid movement.

Flue - Gas or air passage that usually depends on natural convection to cause the combustion gases to flow through it.

Fluid - A gas or liquid 

Flush - Operation to remove any material or fluids from refrigeration system parts by purging them to the atmosphere using refrigerant or other fluids.

Flux – A substance of a joint prior to it being brazed or soldered.

Flux lines - Lines of force of a magnet.

Foaming - Formation of foam in an oil-refrigerant mixture due to rapid evaporation of liquid refrigerant dissolved in the oil.

Foot Pound - Unit of work. A foot-pound is the amount of work done in lifting one pound one foot. 

Force - Is the accumulated pressure and is expressed in pounds.

Forced Convection - Movement of fluids by mechanical force.

Force-Feed Oiling - Lubrication system that uses a pump to force oil to surfaces of moving parts.

Fractionation - A change in composition of a blend by preferential evaporation or condensation of the more or less volatile component.

Free Wheeling - Continued rotation of magnetic clutch on automotive compressor when clutch is disengaged.

Freeze Drying - Uses liquid nitrogen or carbon dioxide to turn fresh food into long lasting, frozen food.

Freezer Burn - Condition applied to food which has not been properly wrapped and that has become hard, dry, and discolored.

Freeze up - Is the formation of ice inside the metering device and causing improper refrigeration to accrue.

Freezing Point - The temperature at with if any more heat is removed it will solidify.

Freezing Point Depression - The temperature at which ice will form in solution of water and salt. 

Freon - Brand name refrigerant manufactured by Dupont.

Frequency -   The number of cycles per second for any periodic waveform - unit : Hertz

Frost Back - This is caused my the flooding of refrigerant liquid in the suction line.

Frost Control, Automatic - Control that automatically cycles refrigerating system to remove frost formation on evaporator.

Frost Control, manual - Manual control used to change operation of refrigerating system to produce defrosting conditions.

Frost Control, Semiautomatic - Control which starts defrost part of a cycle manually and then returns system to normal operation automatically.

Frost Free Refrigerator – A refrigerator that incorporates automatic defrost.

Frosting Type Evaporator - Refrigerating system which maintains the evaporator at frosting temperatures during all phases of cycle.

Frozen - 1-Water in its solid state. 2-Seized (as in machine parts) due to lack of lubrication. The term "freeze-up" is often applied to this situation.

Fuel Oil - Kerosene or any hydrocarbon oil as specified by U.S. Depart­ment of Commerce Commercial Standard CS1 2 or ASTM D296, or the Canadian Government Specification Board, 3-GP-28, and having a flash point not less than 100 0 F (38 0 C1.

Full Floating - Mechanism construction in which a shaft is free to turn in all parts in which it is inserted.

Full Package - Self contained heat pump which has blower and compressor section integrated into one unit.

Furnace, Central – A self-contained appliance designed to supply heated air through ducts to spaces remote from or adjacent to the appliance location.

Fuse - Electrical device that melts a fusible metal strip during an over current condition.

Fusible Link - is a heat sensitive link designed to break in a fire.

Fusible Plug- A heat sensitive plug used on pressure vessels that will let go at a predetermined temperature.

Galvanic Action – The corroding action of two unlike metals due to elec­trical current passing between them.

Gas - The vapor state of a material.

Gas, Non-condensable - Gas that will not form into a liquid under the operating pressure-temperature conditions.

Gas Valve – A device for starting, stopping, or regulating flow of gas.

Gas Regulator – A device for the regulation of gas.

Gasket – A material used to form a leak proof seal between 2 parts.

Gasket, Foam - Joint sealing material made of rubber or plastic foam strips.

Gauge - An instrument to measure pressure or Fluid levels.

Gauge, High Pressure - Used for pressure ranges from 0 psig to 500 psig 1101.3 kPa to 3 600 kPa.

Gauge, Low Pressure - Used for pressure ranges from 0 psia to 50 psia 10 kPa to 350 kPa.

Gauge Manifold - A Chambered device constructed to hold both compound and high-pressure gauges. Valves control flow of fluids through it.

Gauge Port – A connection in a system to provided for a service technician to install a gauge.

Gauge Vacuum – An Instrument used to measure pressures below at­mospheric pressure.

Geothermal Energy - Heat energy stored in the earth's crust by the absorption of solar energy and by conduction with the earth's hot interior.

Glide - The temperature difference between the starting and ending temperatures of a phase change within a system, exclusive of any subcooling or superheating.

Glycerol - Is a lubricant but has found little because of its tendency to rapidly absorb moisture.

Grain - Unit of weight and equal to 1/7000 lb. It is used to indicate the amount of moisture in the air.

Gravity Cooling - Evaporator does not have a fan to distribute the air.

Gravity Heating- heat is distributed by gravity this king of unit has no fan.

Grille - A cover or louvered opening placed in a room at the end of an air passageway.

Grommet - Plastic, metal, or rubber doughnut-shaped protectors which line holes where wires or tubing pass through panels.

Ground, Short circuit – A Fault in an electrical circuit allowing elec­tricity to flow to ground.

Ground Coil - Heat exchanger buried in the ground. May be used either as an evaporator or as a condenser.

Ground Loop - A series of heat exchange pipes  which are buried either vertically or horizontally in the earth.

Ground Source - A refrigeration system which utilizes the earth as it's source of energy.

Ground Wire – An electrical wire that will safely conduct electricity from a structure into the ground.

Halide Refrigerants - Refrigerants containing halogen chemicals.

Halide Torch - A propane torch used in the process of leak checking.

Halogens - Substance containing fluorine, chlorine, bromine, and iodine.

Hanger – A device attached to walls or other structure for support of pipe lines.

Head – Is another word for Pressure.

Head, Static - Is the amount of pressure a pump has to work against.

Head, Total Static - Static head from the surface of the supply source to the free discharge surface.

Head Friction - Head required to overcome friction of the interior sur­face of a conductor and between fluid particles in motion.

Head Pressure - The discharge pressure in the system.

Head Pressure Control - A Pressure actuated safety control which opens elec­trical circuit if high-side pressure becomes too high.

Head Velocity - Height of fluid equivalent to its velocity pressure inflow­mg fluid.

Header - A piping arrangement where several pipes are distributed from one common pipe.

Heat - Basic form of energy that may be partially converted into other forms of energy.

Heat Anticipator - Is a wire-wound variable resistor that is placed near the bimetal element of a thermostat to provide extra sources of heat to help prevent the thermostat from allowing the system to overheat the room.  Connected in series with the R-W circuit. Causes the spiral bi-metal element to open before  room set-point is reached.

Heat Content-  See total heat.

Heat Exchanger - A refrigeration component used to transfer heat from one source to another.

Heat Intensity – The heat in a substance as measured by the dry bulb temperature.

Heat Lag - The time it takes for heat to travel through a substance.

Heat Leakage -Flow of heat through a substance.

Heat Load – The amount of heat removed by a given system over a 24hour period.

Heat Source - The area or media from which heat is removed from .

Heat of Compression - Mechanical energy of pressure changed into energy of heat.

Heat of Fusion - Heat released from a substance when a change of state occurs from a liquid to solid state.

Heat of Respiration - Process by which oxygen and carbohydrates are assimilated by a substance; also when carbon dioxide and water are given off by a substance.

Heat Recovery System - Produces and stores hot water by transfer­ring heat from condenser to cooler water.

Heat Sink - The area or media where heat is absorbed into. 

Heat Transfer - Movement of heat from one body or substance to another.

Heat Transfer Module - Primary system of heat transfer in a glycol water solution forced-air furnace. The heat transfer module contains the ignitor, burner, and primary solution-circulating coil.

Heating Coil - Heat transfer device consisting of a coil of piping, which releases heat.

Heating Control – A device that controls the temperature of a substance by operating a unit which releases heat.

Heating Value - Amount of heat which may be obtained by burning a fuel. The heating value is usually expressed in Btu per lb

Hermetic Compressor – A sealed compressor that the internal motor is not serviceable. housing.

Hermetic Motor - Compressor drive motor sealed within same casing which contains compressor.

Hermetic system - Refrigeration system which has a compressor driven by a motor contained in compressor dome or housing. 

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 Efficiency Gas Furnace – A furnace with efficiencies from 85 to 95 percent.

High Side – The side of the refrigeration system that the condensing takes place.

High Pressure Cut Out – See head Pressure Control

High Side Float – A metering device that controls the level of the liquid refrigerant in the high-pressure side of the device.

High-Vacuum Pump – A pump that can create a vacuum in the 1000 to 1 micron range.

Hollow-Tube Gasket – A sealing device made of rubber or plastic with tubular cross section.

Holdover - The ability to stay cold after heat removal from the evaporator stops.

Horsepower- A unit of power. Work done at a rate of 33,000 foot-pounds per minute, or 550 foot -pounds per second.

Hot Gas Bypass – A piping system that by passes 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 and at predetermined intervals, in order to remove frost from evaporator.

Hot Junction - That part of thermoelectric circuit which releases heat.

Hot water Heating System – A system in which water is circulated through heating coils 

Hot Wire – The wire that has the voltage difference between it and ground.

Humidifier – A device used to add humidity to a space.

Humidistat - A control which is operates the humidifier and is affected by changing humidity 

Humidity – Is Moisture in the air.

HVAC- Heating Ventilation and Air Conditioning

Hydraulics - Branch of physics having to do with the mechanical prop­erties of water and other liquids in motion.

Hydrocarbons - A series of chemicals of similar chemical nature ranging from methane through butane , octane ... to heave oils. 

Hydrochloric Acid - An acid formed when appreciable quantity of moisture are present in A CFC or methyl chloride.

Hydrolysis - Reaction of a CFC with water . Acids are generally formed.

Hydrostatic Pressure - The pressure created when trying to compress a liquid.

Hydrometer - A instrument used to measure specific gravity of a liquid.

Hydraulic – A heating system which circulates a heated fluid, usually water, through baseboard coils by means of a circulating pump which is con­trolled by a thermostat.

Hygrometer – An instrument used to measure the amount of moisture in the air.

Hygroscopic - Ability of a substance to absorb and release moisture and change physical dimensions as its moisture content changes.

Ice Melting Equivalent - (IME-ICE MELTING EFFECT): Amount of heat absorbed by melting ice at 32 0 F (0 0 C1 is 144 Btu per pound of Ice or 288 000 Btu per ton

Identification plate (Name Plate) – A plate mounted on the unit that Provides information such as manufacturer, part number and specifications.

Idler - A pulley used on some belt drives to provide proper belt tension and to eliminate belt vibration.

Ignition Transformer - Transformer designed to provide a high-voltage current. Used in many heating systems to ignite fuel; provides a spark gap.

Impedance - Similar to resistance but applies to AC circuits.  The opposition a component in a circuit offers to the flow of alternating current at a given frequency. If the frequency changes,  the impendence changes too. Impendence is measured in ohms and has the symbol Z with the unit ohms

Impeller – a part of a pump that causes the fluid to move. Similar to a blade.

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

Induction motor - An ac motor that operates on principle of rotating magnetic field. Rotor has no electrical connection, but receives elec­trical energy by transformer action from field windings.

Inductive Reactance – The induction of Electromagnetic energy in a circuit that creates a counter or reverse voltage as the original current changes. It may also be thought of as a resistance since it opposes the flow of alternating current. 

Inductance - A changing current in a coil produces a changing magnetic flux. The changing magnetic flux results in an induced current flowing in the coil. The unit is a Henry .

Infiltration - The passage of outside air into building through doors, cracks around windows, etc.

Infrared Lamp - Electrical device that emits infrared rays; invisible rays just beyond red in the visible spectrum.

Inhibitor – A chemical that prevents corro­sion or oxidation.

Instrument - Used broadly to denote a device that has measuring, recording, indicating, and/or controlling abilities.

Insulation, Electric – A substance which has almost no free electrons.

Insulation, Thermal – A material with low heat conductivity.

Integrated Circuit (IC) - A circuit that incorporates multiple transistors and other semiconductors to a single circuit, sometimes called a "chip."

Intermittent Cycle – A cycle which repeats itself.

Interrupted Cycle – A cycle that does not repeats it self.

Interstate Commerce Commission - Government body which controls the design and construction of pressure containers.

Ion- Group of atoms or an atom electrically charged.

IR Drop – A voltage drop, IR meaning Current times resistance and equaling voltage (Ohm's Law).

Isobutane - A flammable hydrocarbon refrigerant.

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

Isothermal Expansion and contraction - an action which takes place without a temperature change.

Jet Cooling System – A jet pump is used to produce a vacuum so water or refrigerant may evaporate at relatively low temperatures. These systems usually require large condenser and have a low efficiency to remove heat. 

Joint - Connecting point as between two pipes. 

Joule- Metric unit of heat. 

Joule – Thomson Effect - The change in the temperature of a gas on its expansion through a porous plug from a higher pressure to a lower pressure. 

Journal Crankshaft - The part of shaft which contacts the bearing on the large end of the piston rod. 

Junction Box – A box or container housing group of electrical terminals.

Kata Thermometer - An alcohol thermometer used to measure air speed or atmospheric conditions by means of cooling effect.

Kelvin Scale - Thermometer scale on which unit of measurement equals the Celsius degree and according to which absolute zero is 0 degree, the equivalent of -273.16 0 C. Water freezes at 273.16 0 K and boils at 373.16 0 K.

Kilopascal (kPa) - See PASCAL.

Kilowatt - 1000 watts of power or 1.34 horse power.

KWH - Kilowatt hours - Electrical term - 1 Kwh equals the use of 1000 watts for one hour.

Kilovolt Ampere (kVA) - Unit of electrical flow equal to volts multiplied by amperes and divided by one thousand.

Latent Heat- Heat that when added to or removed from a substance causes a change of state but not a change in temperature.

Latent Heat of Evaporation - The amount of heat added to a substance during the change of state.

Lag of temperature control - The delay in action of a temperature element due to the time required for the temperature of the element to reach the medium temperature.

Leak Detector - A device to locate refrigerant leaks.

Liquid Line - The line that caries the high temperature high pressure sub cooled liquid from the receiver  line to the metering device.

Liquid Receiver - A device used to store refrigerant till it is required.

Liquid-to-Air  - A system which absorbs heat from a liquid and rejects it to the air.

Liquid-to-Liquid heat pump - A heat pump which absorbs heat from a liquid and also rejects it to a liquid.

Load - The required rate of heat removal.

Low side - The area of the refrigeration cycle that operates under a lower pressure compared to the high side.

Manometer - A U-shaped device used to measure pressure difference.

Mechanical Cooling - Conventional cooling provided by a mechanical means. Term can be interchanged with "active cooling".

Mechanical Efficiency - The ratio of work done by a machine compared to the amount of energy used.

Megohm - One million ohms.

Methyl Alcohol - is sometimes used as an antifreeze. 

Methyl Chloride - One type of Refrigerant.

Metering Device- A device used to meter the amount of refrigerant entering the evaporator.

Moeller diagrams -  A graphical representation of the thermal properties of fluids with total heat and entropy as coordinates.

Motor - A device used to convert electrical energy into mechanical energy.

Needle Valve - A valve having a slender point fitting into a conical seat, used to regulate accurately the flow of a liquid or gas.

Nipple - A pipe coupling threaded on both ends.

Noncondensables - Gases mixed with refrigerants that cannot be condensed at the same temperature and pressures as refrigerants.

Nonconductors (Insulators) - Nonconductors resist electron flow. The atoms have almost no free electrons. Examples would be: A perfect vacuum, quartz, glass, ceramics, rubber, wood, plastics.

OHM - The unit of resistance usually known as R.

Ohm's Law - Written I = E/R where I is current flowing , V is the voltage and R is the resistance.

Oil Trap - A device to trap oil from leaving the compressor and entering the system.

Open Compressor - A compressor where the motor is not sealed inside the compressor itself. 

Open Loop - A system where water is pumped from a water well, pond, lake or other surface source for use in a heat pump.

Output - The part of the circuit where the process signal is available.

Oversized Evaporator - A evaporator with a greater capacity than the nominal capacity of the  system. 

Ozone - The O 3 from oxygen .It's used as a odor eliminator.

Passive Cooling - A process whereby a secondary refrigerant  is pumped directly to a evaporator and cooling is accomplished without a the operation of a mechanically driven refrigeration system.

Package Heat Pump - A refrigeration system that  has all required components  in one cabinet.

Packless Valve - A valve that does not use packing to prevent leaks.

Power - The rate of doing work measured in watts , horse power ...

Pour Point - The temperature at witch oil will not change is the container is tilted.

Performance Factor - The ratio of heat removed compared to the energy used to do it.

Photocell - A device that changes resistance with light.

Pressure - The force exerted per unit area.

Primary - The input side of a transformer.

Psychrometer - a device used to measure web bulb temperature.

Pyrometer - A device used to  measure high temperatures.

Psychometric Chart - A chart used to determine the specific volume , heat content. dew point, relative humidity , absolute humidity  and dry and wet bulb temperatures.

PSIG- Pounds per square inch gauge pressure.

PSIA - pounds per square inch absolute pressure .  PSIG + Atmospheric pressure (14.7)

Purge - A momentary opening to allow a fluid to escape

Pre Purge - The flushing of air through the combustion and heat exchanger prior to the burner firing.

Post Purge - The flushing of air through the combustion and heat exchanger after the burner has completed firing.

Primary Air - air that mixes with a fuel prior to the fuel being burnt.

Radiant Floor Heating - Process of embedding tubing  directly in a concrete floor so that hot water can be pumped through the tubing for the purpose of heating the floor and thus the building.

Radiation - The passage of heat from one object to one other without warming the space between.

Refrigerant - The medium of heat transfer in a refrigeration system that picks up heat by evaporating at a low temperature and rejects heat by condensing at a high temperature.

Refrigeration system - A combination of parts in witch a refrigerant is circulated for the propose of extracting heat.

Relative Humidity- The amount of moisture in the air compared with the amount of moisture the air can hold.

Relay - An electromechanical device containing a coil and a set of contacts. The contacts close when the coil is energized.

Relief Device - A device designed to open under a high pressure.

Resistance - The opposition to current flow. or the reciprocal of thermal conductivity.

Rotary Compressor- A compressor in witch a compression is attained in a cylinder by rotation of a semi radial member.

Reversing Heat Pump - A heat pump in which the condenser and evaporator coils of the unit reverse roles in response to a reverse in the direction of the flow of refrigerant in the machine.

Running Time - The percentage of time a refrigeration compressor runs.

Saturated Vapor - Vapor of 100 % quality but not superheated.

Schematic - Another name for a circuit diagram. 

Seasonal Coefficient of Performance (SCOP) - Is the average COP over the entire heating season.

Seasonal Energy Efficiency Ratio (SEER) - The average cooling efficiency over an entire cooling season.

Secondary - The output side of a transformer.

Secondary Air - Air that is mixed with a fuel while it is burning.

Sensible Heat - heat that when added to of removed from a substance causes a change of temperature and not a change of state.

Shell and Tube - A heat exchanger that has ca coil inside a shell.

Short-Circuit - An un-intended path that conducts electricity.

Silica gel- A desiccant used for drying refrigerant

Sink Temperature - This is the temperature of the medium  into which the refrigeration system must reject it's heat.

Sludge - A decomposition product formed in a refrigerant due to impurities in the oil or due to moisture.

Solubility - The ability of one material of one material to enter into a solution with another.

Solenoid - A coil of wire that is long compared to its diameter, through which a current will flow and produce a magnetic flux to push or pull a rod.

Source Temperature - This is the temperature of the medium  from which the refrigeration system extracts its heat.

Specific Gravity - The weight of a volume of a material compared to the weight of the same quantity of water.

Specific Heat -  The amount of heat required to raise the temperature of one unit of mass of a substance by one degree.

Specific Volume - The volume of a definite weight of a material.

Split System - A refrigeration system that is housed in one ore more cabinets or split apart .

Standard Air - Air weighing 0.7488 pound per cubic foot, which is air at 68 o F dry bulb and 50% relative humidity at a barometric pressure of 29.92 in. Hg.

Static Pressure - Pressure exerted outward against walls, tubes or ducts.

Sub cooled - Cooled below the saturation temperature of the liquid.

Sublimation - The change of state from a solid to a vapor state without and intermediate liquid state.

Suction Line - The piping between the evaporator outlet and the compressor inlet.

Suction Pressure - The pressure on the low side of the system.

Sulfur Dioxide - A type of refrigerant.

Superheat - Heat added to a substance above it's saturation temperature.

Superheated Gas - A gas temperature higher than the evaporation temperature at the exiting pressure.

Sweating - Condensation from the air on surfaces below the due point of the air.

Temperature-Heat level or pressure . The thermal state of a body with respect to its ability to pick up heat from or pass heat to another body.

Temperature-Control Lag - The delay of action of the temperature response element due to the time required for the element to reach the surrounding temperature.

Temperature, Absolute - The temperature at which molecular motion stops. It is the lowest temperature possible. There is no more heat in a substance at this point.

Temperature, Design - Are the result of a lot of testing and gathering of data in order to help with the design of systems. It is a chart or or data base used to reference average temperatures for most areas across the country.

Temperature, Dry Bulb - It is the temperature measured by thermometers in the home.

Temperature, Wet Bulb - The result of moisture in the air or, the saturation temperature of water presently in the air. It is attained my using a thermometer enclosed with a damp mesh. When air is blown past the thermometer, some of the damp will evaporate causing cooling and lowering the temperature reading. The difference between the  dry bulb and the wet bulb temperatures are an indication of the relative humidity of the air.

Ternary -  Consisting of three single component refrigerants.

Thermistor - Is a heat sensitive resistor that changes resistance with a change in temperature.

Thermocouple - A device consisting of 2 different conductors that when heated creates an electrical potential difference.

Thermodynamic - The study of the mechanics of heat.

Thermometer - A device for indicating temperature.

Thermostat- A temperature sensitive device used to control HVAC systems.

Thermostatic Valve - A precision metering device designed to regulate the rate of refrigerant liquid flow into the evaporator in the exact proportion to the rate of evaporation of refrigerant liquid in the evaporator.

Ton (of refrigeration) - The amount of heat energy ( BTU'S) absorbed in the conversion of 1 Ton of ice to 1 ton of water over a 24hour period  at 32 o F.

Total Pressure - The sum of static pressure and velocity pressure.

Transistor - A three layer sandwich of two different components consisting mainly of silicon semiconductor material. The device acts as a valve and a relay for electron flow.

Transducer - A substance or device, that converts input energy of one form into output energy of another.

Transformer-An electrical device by which alternating current of one voltage is changed to another voltage.

TX Valve - A precision device used to regulate the rate of refrigerant flow into the evaporator to exactly match the rate of refrigerant evaporation .

Unit System - A unit that can be removed from a premises without disconnecting any lines or wiring.

Unloader - A mechanical device used to reduce the capacity of a refrigeration compressor.

Upper fixed point - The higher of two reference points used to "fix" a temperature scale. Example: The boiling point of water at standard temperature and pressure, is the upper fixed point of a Celsius scale.

Vacuum - A pressure below atmospheric.

Vapor Pressure - The pressure exerted on a liquid and vapor surface.

Volt - The unit of voltage.

Voltage - Is a term used to indicate the potential difference in a circuit,  Voltage is also known as the  pressure which causes current to flow. also expressed as electro motive force (EMF).

Voltmeter - A meter for measuring voltage.

Viscosity - The property of fluid to resist flow or change.

Watt - Symbol W. The unit of power.

Water-to-Water - A refrigeration system where the condensing and evaporating medium is water.

Wet Compression - A system of refrigeration in which some liquid refrigerant is mixed with vapor entering the compressor so as to cause the discharge vapors from the compressor to tend to be saturated rather than superheated.

Xylene - A flammable solvent , used to dissolve or loosen sludge.

Zero Absolute - See  Absolute temperature and pressure.

Zeotrope - A blend of refrigerants having a temperature glide greater than 5 o