Glossary of Terms A to H

Absolute Humidity-Amount of moisture in the air, indicated in grains per cubic foot.

Absolute Pressure-Gauge pressure plus atmospheric pressure(14.7 lbs. per sq. in.).

Absolute Temperature-Temperature measured from absolute zero.

Absolute Zero Temperature-Temperature at which all molecular motion ceases. (-460 F. and -275 C.)

Absorbent-Substance which has the ability to take up or absorb another substance.

Absorber-A solution or surface that is capable of soaking up (taking in) another substance or energy form.

Absorption-The process of taking or soaking up into a substance.

Absorption Chiller-A chiller that uses a brine solution and water to provide refrigeration without the aid of a compressor.

Absorption Refrigerator-Refrigerator which creates low temperatures by using the cooling effect formed when a refrigerant is absorbed by chemical substance.

Accelerate-To add to speed; hasten progress of development.

Accessible Hermetic-Assembly of motor and compressor inside a single bolted housing unit.

Accumulator-Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into suction line.

Acid Condition In System-Condition in which refrigerant or oil in system is mixed with fluids which are acid in nature.

ACR Tubing-Tubing used in refrigeration which has ends sealed to keep tubing clean and dry.

Activated Alumina-Chemical used as a drier or desiccant.

Activated Carbon-Specially processed carbon used as a filter-drier; commonly used to clean air.

Active Solar Heating System-A system in which solar energy is absorbed in a collector, stored, and distributed by an auxiliary circulating system.

Actuator-That portion of a regulating valve that converts mechanical fluid, thermal energy, or electrical energy into mechanical motion to open or close valve seats.

Adiabatic Compression-Compressing refrigerant gas without removing or adding heat.

Adsorbent-Substance which has property to hold molecules of fluids without causing a chemical or physical change.

Adsorption-The adhesion of a thin layer of molecules of a gas or liquid to a solid object.

Aeration-Act of combining a substance with air.

Agitator-Device used to cause motion in confined fluid.

Air-An invisible, odorless, and tasteless mixture of gases that surrounds the earth.

Air Break-An inverted opening placed in the chimney of a gas furnace to prevent back pressure from outside wind from reaching the furnace flame or pilot.

Air Cleaner-Device used for removal of airborne impurities.

Air Coil-Coil used with some types of heat pumps which may be used either as an evaporator or as a condenser.

Air Conditioner-Device used to control temperature, humidity, cleanliness, and movement of air in conditioned space.

Air-Cooled Condenser-Heat of compressor is transferred from condensing coils to surrounding air. This may be done either by convection or by a fan or blower.

Air Cooler-Mechanism designed to lower temperature of air passing thought it.

Air Core Solenoid-A solenoid that has a hollow core instead of a solid core.

Air Curtain-A system in which a blower is activated when a door is opened to blow across the open area, preventing the transfer of air between outdoors and indoors.

Air Cycle, Air Conditioning-System which removes heat from air and transfers this heat to air.

Air Defrosting-Evaporator defrosting that occurs as evaporator warms when the compressor is not running.

Air Diffuser-Air distribution outlet designed to direct air flow into desired patterns.

Air Gap-The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.

Air Handler-Fan-blower, heat transfer coil, filter, and housing parts of a system.

Air Sensing Thermostat-Thermostat unit in which sensing element is located in refrigerated spade.

Air Spill-Over-Refrigerating effect formed by cold air from freezing compartment in refrigerator spilling over, or flowing into normal storage area of refrigerator.

Airtight-Sealed to prevent the passage of gas.

Air-To-Air Heat Pump-A heat pump that used outdoor air, as opposed to a geothermal heat pump.

Air Vent-Valve used to remove air from the highest point of a coil or piping assembly.

Air Washer-Device used to clean air, which may increase or decrease humidity.

Alcohol Brine-Water and alcohol solution which remains a liquid at below 32 F.

Algae-Low form of plant life, found floating free in water.

Allen-Type Screw-Screw with recessed head designed to be turned with hex shaped wrench.

Allen Wrench-Hexagon (6-point) tip used to fit socket head screws or setscrews.

Alternating Current(AC)-Electric current in which direction of flow alternates or changes. In 60 cycle current direction of flow reverses every 120th second.

Altitude-The height at a point above a reference level, sea level, or the earth's surface.

Altitude Adjustment-Adjusting refrigerator controls so unit will operate efficiently at altitude in which it is to be used.

Ambient Compensator-An electronic device that provides a small amount of heat to the refrigeration compartment to ensure that the machinery continues to cycle when ambient temperatures are low.

Ambient Temperature-Temperature of fluid (usually air) which surrounds object on all sides.

American Standard Pipe Thread-Type of screw thread commonly used on pipe and fittings to ensure a tight seal.

Ammeter-An electric meter used to measure current, calibrated in amperes.

Ammonia-Chemical combination of nitrogen and hydrogen (NH3). Ammonia refrigerant is identified by R-117.

Amperage-Electron or current flow of one coulomb per second past given point in circuit.

Ampere-Unit of electric current equivalent to flow of one coulomb per second.

Ampere-Turns-Term used to measure magnetic force. Represents product of amperes times number of turns in coil of electromagnet.

Amplifier-Electrical device which increases electron flow in a circuit.

Anemometer-Instrument for measuring the rate of flow of air.

Angle Valve-Type of globe valve design, having pipe openings at right angles to each other. Usually, one opening is in the horizontal plane and one is in the vertical plane.

Anhydrous Calcium Sulfate-Dry chemical made of calcium, sulfur and oxygen (CaSO4).

Annealing-Process of heat treating metal to obtain desired properties of softness and ductility (easy to form into new shape).

Annual Fuel Utilization Efficiency (AFUE) Rating-A rating system for for furnaces that compares energy input and energy output.

Anode-Positive terminal of electrolytic cell.

Anticipator-A device used with a start-stop control to reduce the control differential.

Arcing-Band of sparks formed when an electrical discharge form a conductor jumps to another conductor.

ARI-Air-Conditioning and Refrigeration Institute.

Armature-Revolving part in electric motor or generator.

Articulated Connecting Rods-Short connecting rods in a compressor.

A.S.A.-Formerly, abbreviation for American Standards Association, Now known as United States of America Standards Institute.

Asbestos-Strong, fire-resistant, cancer-causing silicate.

ASME Boiler Code-Standard specifications issued by the American Society of Mechanical Engineers for the construction of boilers and pressure vessels.

Aspect Ratio-Ratio of length to width of rectangular air grille or duct.

Aspirating Psychometer-A device which draws sample of air through it for humidity measurement purposes.

Aspiration-Movement produced in a fluid by suction.

ASTM Standards-Standards issued by the American Society for Testing and Materials.

Atmospheric Dust Spot Efficiency-Measurement of a device's ability to remove atmospheric air from test air.

Atmospheric Pressure-Pressure that gases in air exert upon the earth; measured in pounds per square inch.

Atom-Smallest particle of element that can exist alone or in combination.

Atomize-Process of changing a liquid to minute particles, or a fine spray.

Attenuate-Decrease or lessen in intensity.

Auger-Device with a helical shaft that, when rotated, can be used to move material.

Automatic Control-Valve action reached through self-operated or self-actuated means, not requiring manual adjustment.

Automatic Defrost-System of removing ice and frost from evaporators automatically.

Automatic Expansion Valve(AEV)-Pressure controlled valve which reduces high pressure liquid refrigerant to low pressure liquid refrigerant.

Automatic Ice Cube Maker-Refrigerating mechanism designed to produce ice cubes in quantity automatically.

Autotransformer-A transformer in which both primary and secondary coils have turns in common. Step-up or step-down of voltage is accomplished by taps on common winding.

Auxiliary Evaporator-Small evaporator consisting of coils of tinned tubing below the shelves in a display case.

Azeotropic Mixture-Example of azeotropic mixture--refrigerant R-502 is mixture consisting of 48.8% refrigerant R22, and 51.2% R-115. The refrigerants do not combine chemically, yet azeotropic mixture provides refrigerant characteristics desired.

Back Pressure-Pressure in low side of refrigerating system; also called suction pressure or low side pressure.

Back Seating-Fluid opening/closing such as a gauge opening; to seat the joint where the valve stem goes through the valve body.

Bacteria-A form of unicellular microorganisms.

Baffle-Plate or vane used to direct or control movement of fluid or air within confined area.

Balance Point-The point at which the heating capacity of a heat pump is equal to the heat losses of the structure it is heating.

Ball Check Valve-Valve assembly (ball) which permits flow of fluid in one direction only.

Balloon Type Gasket-Flexible refrigerator door gasket having a large cross section.

Bar-Unit of pressure. One bar equals l9869 atmosphere (approximately one atmosphere, 14.51 psi).

Barometer-Instrument for measuring atmospheric pressure. It may be calibrated in pounds per square inch or in inches of mercury in column.

Bath-A liquid solution used for cleaning, plating or maintaining a specified temperature.

Battery-Electricity producing cells which use interaction of metals and chemicals to create electrical current flow.

Baudelot Cooler-Heat exchanger in which water flows by gravity over the outside of the tubes or plates.

Bearing-Low friction device for supporting and aligning a moving part.

Bellows-Corrugated cylindrical container which moves as pressures change, or provides a seal during movement of parts.

Bellows Seal-Method of sealing the valve stem. The ends of the sealing material are fastened to the bonnet and to the stem. Seal expands and contracts with the stem level.

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

Bending Spring-Coil spring which is mounted on inside or outside to keep tube from collapsing while bending it.

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

Bimetal Strip-Temperature regulating or indicating device which works on principle that two dissimilar metals with unequal expansion rates, welded together, will bend as temperatures change.

Bioaerosals-Airborne microorganisms derived from viruses, bacteria, fungi, protozoa, mites, and pollen.

Blast Freezer-Low-temperature evaporator that uses a fan to force air over the evaporator surface.

Bleeding-Slowly reducing the pressure of liquid or gas from a system by opening a valve slightly.

Bleed-Valve-Valve with small opening inside which permits a minimum fluid flow when valve is closed.

Blend-A mixture of various refrigerants.

Blown-With respect to fuses, a fuse that has been melted, breaking the electric circuit and preventing overload.

Boiler-Closed container in which a liquid may be heated and vaporized.

Boiler, High Pressure-A boiler operating with water temperature and water pressure above low-pressure boiling ratings.

Boiler Horsepower-Seldom-used term equivalent to a heating capacity of 33,475 Btu/hr. (9804 watts).

Boiler, Low Pressure-A boiler operating with up to 250 deg. F. (121 deg. C.) water temperature and 160 psi water pressure or less.

Boiling Point-The temperature of a liquid at which it changes to a gas under a pressure of 14.7 psia (101.3 KPa).

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

Bonnet-In a furnace, the sheet metal chamber where heat collects before being distributed.

Booster-Common term applied to the use of a compressor as the first stage in a cascade refrigerating system.

Bore-Inside diameter of a cylindrical hole.

Bourdon Tube-As used in pressure guages. Thin walled tube of elastic metal flattened and bent into circular shape, which tends to straighten as pressure inside is increased.

Bowden Cable-Tube containing a wire used to regulate a valve or control from a remote point.

Boyle's Law-Law of Physics--volume of a gas varies as pressure varies, if temperature remains the same. Examples: If pressure is doubled on quantity of gas, volume becomes one half. If volume becomes doubled, gas has its pressure reduced by one half.

Brazing-Method of joining metals with nonferrous filler (without iron) using heat between 800 deg. F. and melting point of base metals.

Breaker Strip-Strip of wood or plastic used to cover joint between outside case and inside liner of refrigerator.

Breeching-Space in hot water or steam boilers between the end of the tubing and the jacket.

Brine-Water saturated with chemical such as salt.

British Thermal Unit(BTU)-the amount of heat required to raise the temperature of one pound of water (about one pint) by one degree Fahrenheit.

Building Related Illness (BRI)-An illness caused by an airborne virus in a building.

Built-Up Terminal-Electrical terminal attached to a compressor dome.

Bulb, Sensitive-Part of sealed fluid device which reacts to temperature to be measured, or which will control a mechanism.

Bunker-In commercial installations, space in which ice or cooling element is installed.

Burner-Device in which combustion of fuel takes place.

Butane-Liquid hydrocarbon (C4H10) commonly used as fuel for heating purposes.

Bypass-Passage at one side of, or around regular passage.

Bypass Cycle-A cycle using a bypass line with either hot gas or liquid used to defrost an evaporator or for low pressure control

Cabinet-The housing of a refrigerator.

Cabinet Volume-The volume of the interior cabinet dimensions.

Cadmium Plated-Parts coated with thin corrosion-resistant covering of cadmium metal.

Calcium Sulfate-Chemical compound (CaSO4) which is used as a drying agent or desiccant in liquid line dryers.

Calibrate-to determine; position indicators as required to obtain accurate measurements.

Callback-A service call to repair a problem that had been improperly repaired.

Calorie-Heat required to raise temperature of one gram of water one degree centigrade.

Calorimeter-Device used to measure quantities of heat or determine specific heats.

Cam-Oblong mechanical component that produces a reciprocating motion when rotated.

Capacitance (C)-Property of nonconductor (condenser or capacitor) that permits storage of electrical energy in an electrostatic field.

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

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.

Capillary Tube-A type of refrigerant control. Usually consists of several feet of tubing having small inside diameter. Friction of liquid refrigerant and bubbles of vaporized refrigerant within tube serve to restrict flow so that correct high side and low side pressures are maintained while the compressor is operating. A capillary tube refrigerant control allows high side and low side pressures to balance during off cycle. Also; a small diameter tubing used to connect temperature control bulbs to control mechanisms.

Carbon Dioxide(CO2)-Compound of carbon and oxygen which is sometimes used as a refrigerant. Refrigerant number is R-744.

Carbon Dioxide Indicator-Instrument used to indicate the percentage of carbon dioxide in stack gases.

Carbon Filter-Air filter using activated carbon as air cleansing agent.

Carbon Monoxide (CO)-Colorless, odorless, and poisonous gas produced when carbon fuels are burned with too little air.

Carbon Tetrachloride-A colorless nonflammable liquid used as solvent and in fire extinguishers. Very toxic. Should never be allowed to touch skin, or fumes inhaled.

Carrene-A refrigerant in group 1 (R-11). Chemical combination of carbon, chlorine and flourine.

Cascade Systems-Arrangement in which two or more refrigerating systems are used in series; uses cooling coil of one machine to cool condenser of other machine. Produces ultra-low temperatures.

Casehardened-Heat treating ferrous metals (iron) so surface layer is harder than interior.

Cathode-Negative terminal of an electrical device. Electrons leave the device at this terminal.

Cavitation-Localized gaseous condition within a liquid stream.

Celsius-German language word for centigrade, the metric system temperature scale.

Centigrade Scale-Temperature scale used in metric system. Freezing point of water is 0; boiling point 100.

Centimeter-Metric unit of linear measurement which equals .3937 inches.

Central Air Conditioning-A system capable of providing heating, cooling, humidifying, an dehumidifying.

Centralized Computer Control-Energy control device, centrally located, that makes control decisions based on operating date, programmed information, and stored data. Can be used to optimized energy consumption of many devices throughout a building.

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.

Centrifugal Compressor-Compressor which compresses gaseous refrigerants by centrifugal force.

Centrifugal Force-Force that pushes a rotating object away from the center of its rotation.

Centrifugal Switch-An electrical switch that is opened and closed by centrifugal force.

Ceramic Ignitor-Electric ignition system used in a water glycol solution, forced-air furnace. Electrically heated to create ignition of the gas-air mixture in the combustion chamber.

Change Of State-Condition in which a substance changes from one state (solid, liquid, or gas) to another.

Charge-Amount of refrigerant placed in a refrigerating unit.

Charging Board-Specially designed panel of cabinet fitted with gauges, valves and refrigerant cylinders used for charging refrigerant and oil into refrigerating mechanisms.

Charles' Law-the volume of a give mass of gas at a constant pressure varies according to its temperature.

Check Valve-A device which permits fluid flow only in one direction.

Chemical Refrigeration-A system of cooling using a disposable refrigerant.

Chiller-Air conditioning system that circulates chilled water to various cooling coils in an installation.

Chill Factor-Calculated number, based on temperature and wind velocity, that indicated chill effect.

Chimney-Vertical shaft enclosing one or more flues for carrying flue gases to the outside atmosphere.

Chimney Connector-Conduit (pipe) connecting the furnace to the vertical flue.

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

Chimney Flue-Flue gas passageway in a chimney.

Chlorofluorocarbons (CFCs)-Refrigerants that are composed of chlorine, fluorine, and a hydrocarbon (methane). CFCs deplete the ozone layer.

Choke Tube-Throttling device used to maintain correct pressure difference between high side and low side in refrigerating mechanism. Capillary tubes are sometimes called choke tubes.

Circuit-A tubing, piping or electrical wire installation which permits flow from the energy source back to energy source.

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

Circuit, Parallel-arrangement of electrical devices in which all positive terminals are joined to one conductor and all negative terminals to other conductor.

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

Circuit Series-Electrical wiring: electrical path (circuit) in which electricity to operate second lamp or device must pass through first, and so on; current flow travels through all devices connected together.

Clean Room-A room in which special efforts are made to eliminate dust and other contaminants.

Clearance Pocket Compressor-A small space in cylinder from which compressed gas is not completely expelled. This space is called the compressor operation, compressors are designed to have as small clearance space as possible.

Clearance Space-Small space in a cylinder from which compressed gas is not completely expelled. For effective operation, compressors and designed to have as small a clearance space as possible.

Climate-The average weather conditions for a region.

Climate Control-Devices used to maintain an ideal climate in a space.

Closed Circuit-An electrical circuit in which electrons are flowing.

Clutch, Armature-The part of the automotive compressor magnetic clutch which is attracted by the magnetic field and causes the compressor to be turned by a belt drive when the magnetic field is energized.

Clutch, Field-The coils of wire through which the current flows to create the magnetic force which engages the magnetic clutch.

Clutch, Magnetic-Clutch built into automobile compressor flywheel, operated magnetically, which allows pulley to revolve without driving compressor when refrigerating effecting is not required.

Code Installation-A refrigeration or air conditioning installation which conforms to the local code and/or the national code for safe and efficient installations.

Coefficient Of Conductivity-The measure of the relative rate at which different materials conduct heat. Copper is a good conductor of heat and therefore, has a high coefficient of conductivity.

Coefficient Of Expansion-A measure of the change in size of a material as the temperature changes.

Coefficient Of Performance(COP)-a ratio calculated by dividing the refrigerant system, including circulating fan heat but excluding supplementary resistance (BTU's per hour), by the total electric input (watts) x 3.412. The ratio of work or energy applied as compared to the energy used.

Cogeneration-Using waste energy as a primary heat source. Example: The use of waste heat from an electrical energy generation system to heat a building.

CO2 Indicator-An instrument used to indicate the percent of carbon dioxide in stack gases.

Cold-Cold is the absence of heat; a temperature considerably below normal.

Cold Ban-A plastic trim piece used to reduce heat flow between the outer and inner shell of a refrigerator door.

Cold Junction-That part of a thermoelectric system which absorbs heat as the cooling system operates.

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

Collector-Semiconductor section of a transistor, connected to the same polarity as the base.

Colloids-Miniature cells in meat, fish and poultry.

Combined Annual Efficiency (CAE) Ratio-Rating system used for combined heating systems, which heat both air and water.

Combustible Liquids-Liquid having a flash point above 140 deg. F. (60 deg.C.); known as Class 3 liquids.

Combustion-The process of igniting and burning.

Comfort Chart-Chart used in air conditioning to show the dry bulb temperature and humidity for human comfort conditions.

Comfort Cooler-A system used to reduce the temperature in the living space in homes. These systems are not complete air conditioners as they do not provide complete control of heating, humidifying, dehumidification, and air circulation.

Comfort Zone-Area on psychrometric chart which shows conditions of temperature, humidity, and sometimes air movement, in which most people are comfortable.

Commercial System-A refrigeration or air conditioning unit that is used in commercial buildings.

Commutator-Part of electric motor rotor which conveys electric current to rotor windings.

Complaint-Statement of dissatisfaction with regards to a service.

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

Compound Pump-A rotary pump that has two rotors in series.

Compound Refrigerating Systems-System which has several compressors or compressor cylinders in series. The system is used to pump low pressure vapors to condensing pressures.

Compound Wound-Winding used in motors that run on dc current.

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

Compression Chiller-A chiller that achieves the required pressure difference through the use of a compressor.

Compression Gauge-Instrument used to measure positive pressures (pressures above atmospheric pressures) only. These gauges are usually calibrated from 0 to 300 pounds per square inch of pressure, gauge, (psig).

Compression Ratio-Ratio of the volume of the clearance space to the total volume of the cylinder. In refrigeration it is also used as the ratio of the absolute lowside pressure to the absolute high-side pressure.

Compression Ring-Upper piston ring.

Compressor-The pump of a refrigerating mechanism which draws a vacuum or 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, External Drive-See Compressor, Open-Type.

Compressor, Hermetic-Compressor in which driving motor is sealed in the same dome or housing that contains the compressor.

Compressor, Multiple-Stage-A compressor having two or more compressive steps. Discharge from each step is the intake pressure of the next in series.

Compressor, Open-Type-Compressor in which the crankshaft extends through the crankcase and is driven by an outside motor.

Compressor, Reciprocating-Compressor which uses a piston and cylinder mechanism to provide pumping action.

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

Compressor Seal-Leakproof seal between crankshaft and compressor body.

Compressor, Single-Stage-Compressor having only one compressive step between low-side pressure and high side pressure.

Computer-Series of electrical components which accepts inputs from an operator and controls outputs.

Computer Languages-Specific working or codes, such as BASIC, FORTRAN, COBOL, and C, which direct a computer to accept and store information and control outputs.

Condensate-Fluid which forms on an evaporator.

Condensate Pump-Device used to remove fluid condensate that collects beneath an evaporator.

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

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

Condenser-The part of refrigeration mechanism which receives hot, high pressure refrigerant gas from compressor and cools gaseous refrigerant until it returns to liquid state.

Condenser, Air-Cooled-A heat exchanger which transfers surrounding air.

Condenser Comb-Comb-like device, metal or plastic, which is used to straighten the metal fins on condensers or evaporators.

Condenser Fan-Forced air device used to move air through air-cooled condenser.

Condenser, Water-Cooled-Heat exchanger which is designed to transfer heat from hot gaseous refrigerant to water.

Condenser Water Pump-Forced water moving device used to move water through condenser.

Condensing Furnace-High-efficiency, gas forced-air furnace that extracts the latent heat lost in conventional gas forced-air furnaces.

Condensing Pressure-Pressure inside a condenser at which refrigerant vapor gives up its latent heat of vaporization and becomes a liquid. This varies with the temperature.

Condensing Temperature-Temperature inside a condenser at which refrigerant vapor gives up its latent heat of vaporization and becomes a liquid. This varies with the pressure.

Condensing Unit-That part of refrigerating mechanism which pumps vaporized refrigerant from evaporator, compresses it, liquefies it in the condenser and returns the liquid it in the condenser and returns the liquid refrigerant to refrigerant control.

Condensing Unit Service Valves-Shutoff hand valves mounted on condensing unit to enable serviceman to install and/or service unit.

Conduction-The flow of heat between substances by molecular vibration.

Conductivity-Ability of a metal or a substance to conduct or transmit heat and/or electricity.

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

Connecting Rod-That part of compressor mechanism which connects piston to crankshaft.

Console-A total unit or system of controls located in one area and enclosed. A window air conditioner is a console air conditioner.

Constant-Remains the same; unchanging.

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

Contaminant-A substance (dirt, moisture, or other substance) foreign to refrigerant or refrigerant oil in system.

Continuous Cycle Absorption System-System which has a continuous flow of energy input.

Continuous Operation-In constant use.

Contractual Agreement-A written arrangement, enforceable by law, that is entered into between two parties.

Control-Automatic or manual device used to stop, start and/or regulate flow of gas, liquid, and/or electricity.

Control, Compressor-See Motor Control.

Control, Defrosting-Device to automatically defrost evaporator. It may operate by means of a clock, door cycling mechanism, or during "off" portion of refrigerating cycle.

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

Control Module-An electrical component used in automotive air conditioning systems to receive sensor input and regulate climate control functions. Also referred to as a microcomputer.

Control, Motor-A temperature or pressure operated device used to control running of motor.

Control, Pressure Motor-A high or low pressure control which is connected into the electrical circuit and used to start and stop motor when there is need for refrigeration or for safety purposes.

Control, Refrigerant-Device used to regulate flow of liquid refrigerant into evaporator; such as capillary tube, expansion valves, high and low side float valves, etc.

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

Control, Temperature-A thermostatic device which automatically stops and starts motor, operation of which is based on temperature changes.

Control Valve-Valve that regulates the flow or pressure of a medium that affects a controlled process. Control valves are operated by remote signals from independent devices using any of a number of control media such as pneumatic, electric, or electrohydraulic.

Controlled Evaporator Pressure-Controlled system which maintains definite pressure or range or pressures in evaporator.

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

Convection-Transfer of heat by means of movement or flow of a fluid or gas.

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.

Conversion Factors-Force and power may be expressed in more than one way. A horsepower is equivalent to 33,000 foot pounds of work per minute, 746 watts, or 2,546 Btu per hour. These values can be used for changing horsepower into foot pounds, Btu or watts.

Cooler-Heat exchanger that removes heat from a substance.

Cooling Coil-Coils cooled by a fluid that does not evaporate (such as brine). The evaporator is sometimes incorrectly referred to as a cooling coil.

Cooling Tower-Device which cools water by water evaporation in air. Water is cooled to wet bulb temperature of air.

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

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

Core, Magnetic-Magnetic center of a magnetic field.

Core Valves-Shrader valve used to gain access to a hermetic unit.

Corrosion-Deterioration of materials from chemical action.

Coulomb-Quantity of electricity transferred by electric current of one ampere in one second.

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

Counterflow-Flow in opposite direction.

"Cracking" A Valve-Opening valve a small amount.

Crankshaft Seal-Leakproof joint between crankshaft and compressor body.

Crankthrow-Distance between center line of main bearing journal and center line of the crankpin or eccentric.

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-Condition of refrigerant at which liquid and gas have same properties.

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

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

Cross-charged-Sealed container containing two fluids which together create a desired pressure-temperature curve.

Cryogenic Food Freezing-See Fast Food Freezing.

Cryogenic Fluid-Substance which exists as a liquid or gas at ultra-low temperatures (-250 F. or lower).

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

Current (I)-Transfer of electrical energy in conductor by means electrons changing position.

Current-Limiting Fuse-A fuse that protects an electrical circuit by limiting the amount of current that flows through it, but does not "blow."

Current Relay-Device which opens or closes or a circuit based on change of current flow.

Customer Relations-The evaluation of the technician by the customer as a result of the technician's job performance and attitudes.

Cut-In-Temperature or pressure valve which closes control circuit.

Cut-Out-Temperature or pressure valve which opens control circuit.

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

Cylinder-1. Device that converts fluid power into linear mechanical force and motion. This usually consists of movable elements such as a piston and piston rod, plunger or ram, operating within a cylindrical bore. 2. Closed container for fluids.

Cylinder Head-Part which encloses compression end of compressor cylinder.

Cylinder, Refrigerant-Cylinder in which refrigerant is purchased and dispensed. Color code painted on cylinder indicates kind of refrigerant cylinder contains.

Cylindrical Commutator-Commutator with contact surfaces parallel to the rotor shaft.

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

Damper-Valve for controlling airflow.

Dasher-Stirring mechanism in a dispensing freezer.

Deaeration-Act of separating air from a substance.

Decibel (dB)-Unit used for measuring relative loudness of sounds. One decibel is equal to approximate difference of loudness ordinarily detectable by human ear, the range of which is about 130 decibels on scale beginning with one for faintest audible sound.

Deck (Coil Deck)-Insulated horizontal partition between refrigerated space and evaporator space.

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

Defrost Timer-Device connected into electrical circuit which shuts unit off long enough to permit ice and frost accumulation on evaporator to melt.

Defrosting-Process of removing frost accumulation from evaporators.

Defrosting Evaporator-An evaporator operating at such temperatures that ice and frost on surface melts during off part of operating cycle.

Degreasing-Solution or solvent used to remove oil or grease from refrigerator parts.

Degree-Day-Unit that represents one degree of difference from given point in average outdoor temperature of one day and is often used estimating fuel requirements for a building. Degree-days are based on average temperature over a 24 hour period. As an example; if an average temperature for a day is 50 F., the number of degree-days for that day would be equal to 65 F. minus 50 F. or 15 degree-days (65-50 = 15). Degree-days are useful when calculating requirements for heating purposes.

Dehumidifier-Device used to remove moisture from air in enclosed space.

Dehydrated Oil-Lubricant which has had most of water content removed (a dry oil).

Dehydrator-(See Drier.)

Dehydrator-Receiver-A small tank which serves as liquid refrigerant reservoir and which also contains a desiccant to remove moisture. Used on most automobile air conditioning installations.

De-ice Control-Device used to operate refrigerating system in such a way as to provide melting of the accumulated ice and frost.

Delta Transformer-A three-phase electrical transformer with has ends of each of three windings electrically connected.

Demand Meter-An instrument used to measure kilowatt-hour consumption of a particular circuit or group of circuits.

Density-Closeness of texture of consistency.

Deodorizer-Device which absorbs various odors, usually by principle of absorption. Activated charcoal is a common substance used.

Department Of Transportation (DOT)-A governmental unit that regulates the transportation of refrigerants from one location to another.

Desert Bag-A bag used to keep water cool in the desert. The fabric is not waterproof, so water leaks through and evaporates, cooling the water inside the bag.

Desiccant-Substance used to collect and hold moisture in refrigerating system. A drying agent. Common desiccants are activated alumina, silica gel.

Design Pressure-Highest pressure expected during operation. Sometimes calculated as operating pressure plus a safety allowance.

Detector, Leak-Device used to detect and locate refrigerant leaks.

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

Dew Point-Temperature at which vapor (at 100 percent humidity) begins to condense and deposit as liquid.

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

Diagnostics-The process of identifying or determining the nature and circumstances of an existing condition.

Diaphragm-Flexible membrane usually make of thin metal, rubber, or plastic.

Dichlorodifluromethane-Refrigerant commonly known as R-12. Chemical formula is CCl2F2. Cylinder color code is white. Boiling point at atmospheric pressure is -21.62 F.

Die Cast-A process of moulding low melting temperature metals in accurately shaped metal moulds.

Die Stock-Tool used to hold dies with external threads.

Dielectric Fluid-Fluid with high electrical resistance.

Dies (Thread)-Tool used to cut external threads.

Differential-As applied to refrigeration and heating: difference between "cut-in" and "cut-out" temperature or pressure of a control.

Diffuser-Attachments for duct openings that distribute the air in a wide flow patterns.

Diode-A two-element electron tube which will allow more electron flow in one direction on a circuit than in the other direction; tube which serves a rectifier.

Direct Current (DC)-Electron flow which moves continuously in one direction in circuit.

Direct Digital Control(DDC)-Use of digital computer to perform required automatic control operations in a total energy management system.

Direct Expansion Evaporator-An evaporator coil using either an automatic expansion valve (AEV) or a thermostatic expansion valve (TEV) refrigerant control.

Direct-Spark Ignition-A furnace control in which a spark is used to ignite the gas-air mixture. There is no constantly-burning pilot light.

Dispensing Freezers-A freezer with built-in dispensing equipment, used for serving ice cream and frozen drinks.

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

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

Distilling Apparatus-Fluid reclaiming device used to reclaim used refrigerants. Reclaiming is usually done by vaporizing and then recondensing refrigerant.

Distribution Controls-Systems that help evenly and efficiently transfer the heating or cooling to large residential and industrial areas.

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

DOE-Department of Energy.

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

Door Heater-A heater located around the door opening of a freezer, used to prevent ice buildup from freezing the door closed.

Double Duty Case-Commercial refrigerator which has part of it for refrigerated storage and part equipped with glass windows for display purposes.

Double-Thickness Flare-Copper, aluminum or steel tubing end which has been formed into one assembly part and slipped into another assembly part to insure accurate alignment.

Dowel Pin-Accurately dimensioned pin pressed into one assembly part and slipped into another assembly part to ensure accurate alignment.

Downflow Furnace-A furnace in which return air enters through the top and is pulled down through the heat exchanger. Also called counterflow furnace.

Draft Gauge-Instrument used to measure air movement.

Draft Indicator-An instrument used to indicate or measure chimney draft or combustion gas movement. Draft is measured in units of .1 inch of water column.

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

Drier-A substance or device used to remove moisture from a refrigeration system.

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

Dry Bulb-An instrument with sensitive element which measures ambient (moving) air temperature.

Dry Bulb Temperature-Air temperature as indicated by ordinary thermometer.

Dry Capacitor Condenser-An electrical device made of dry metal and dry insulation, used to store electrons.

Dry Cell Battery-Electrical device used to provide DC electricity, having no liquids in the cells.

Dry Ice-A refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas (sublimates). Its subliming temperature is 109 F. below zero.

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

Dual-Pressure Regulator-A combination of a high-pressure and a low-pressure regulator.

Duct-Heating and air conditioning. A tube or channel through which air is conveyed or moved.

Duct Sweeper-A tool used to remove dirt and debris from ducts.

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

Ebulator-A pointed or sharp edged solid substance inserted in flooded type evaporators to improve evaporation (boiling) of refrigerant in coil.

Eccentric-A circle or disk mounted off center. Eccentrics are used to adjust controls and connect compressor driveshafts to pistons.

Econimizer-A mechanism that removes flash gas from the evaporator.

Eddy Currents-Induced currents flowing in a core.

EER-See Energy Efficiency Ratio.

Effective Area-Actual flow area of an air inlet or outlet. Gross area minus area of vanes or grille bars.

Effective Latent Heat-The amount of heat absorbed from the cabinet and evaporator.

Effectiveness (Absorption Systems)-Method of evaluating absorption cooling systems, in which the cooling effect is divided by the work equivalent to the heat supplied to the absorber.

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. In a compressor, the efficiency would be the work output, as measured by pressure change, divided by the energy input (usually electrical).

Ejector-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 and frost off evaporators during defrosting..

Electrical Circuits-The electrical wiring that permits flow from the energy source, through the circuit, and back to the energy source.

Electrical Resistance-A resistance to (working against) the movement of electrons (flow of electricity).

Electric Heating-House heating system in which heat from electrical resistance units is used to heat rooms.

Electricity-Electric current or power.

Electric Water Valve-Solenoid type (electrically operated) valve used to turn water flow on and off.

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

Electrolux System-Trade name for a continuously operating absorption type of refrigerating system.

Electrolysis-A chemical change in a substance caused by movement of electricity.

Electrolytic Condenser-Capacitor-Plate or surface capable of storing small electrical charges. Common electrolytic condensers are formed by rolling thin sheets of foil between insulating materials. condenser capacity is expressed in microfarads.

Electromagnet-Made by winding coil of wire around soft iron core, When electric current is run through wire, coil becomes a magnet.

Electromagnet Energy-Energy that has both electrical and magnetic characteristics. Solar energy is electromagnetic.

Electromotive Force (EMF) Voltage-Electrical force which causes current (free electrons) to flow or move in an electrical circuit. Unit of measurement is the volt.

Electron-Elementary particle or portion of an atom which 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-Electronic instrument which measures electronic flow across gas gasp. Electronic flow changes indicates presence of refrigerant gas molecules.

Electronic Relay-Electronic switch, such as a triac, that controls a power consuming device.

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

Electronic Sound Tracer-Instrument used to detect leaks by locating source of high frequency sound caused by leak.

Electrostatic Filter-Type of filter which gives particles of dust electric charge. This causes particles to be attracted to plate so they can be removed from airstream or atmosphere.

End Bell-End structure of electric motor which usually holds motor bearings.

End Play-Slight movement of shaft along center line.

Energy Efficiency Ratio(EER)-a ratio calculated by dividing the cooling capacity in Btu's per hour(Btuh) by the power input in watts or any given set of rating conditions, expressed in Btuh per watt (Btuh/watt).

Enthalpy-Total amount of heat in one pound of a substance calculated from accepted temperature base. Temperature of 32 deg. F. is accepted base for water vapor calculation. For refrigerator calculations, accepted base is -40 deg. F.

Entropy-Mathematical factor used in engineering calculations. Energy in a system.

Enzyme-A complex organic substance originating from living cells that speeds up chemical changes in foods. Enzyme action is slowed by cooling.

EPA-See Environmental Protection Agency.

Epoxy (Resins)-A synthetic plastic adhesive.

Equalizer Tube-Device used to maintain equal pressure or equal liquid levels between two containers.

Evaporation-A term applied to the changing of a liquid to a gas. Heat is absorbed in this process.

Evaporative Condenser-A device which uses open spray or spill water to cool a condenser. Evaporation of some of the water cools the condenser water and reduces water consumption.

Evaporator-Part of a refrigerating mechanism in which the refrigerant vaporizes and absorbs heat.

Evaporator Coil-Device made of a coil of tubing which functions as a refrigerant evaporator.

Evaporator, Dry Type-An evaporator into which refrigerant is fed from a pressure reducing device. Little or no liquid refrigerant collects in the evaporator.

Evaporator Fan-Fan which cools extended heat exchange surface of evaporator.

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

Expansion Valve-A device in refrigerant system which maintains a pressure difference between the high side and low side and is operated by pressure.

Expendable Refrigerant System-System which discards the refrigerant after it has evaporated.

External Equalizer-Tube connected to low pressure side of an expansion valve diaphragm and to exit of evaporator.

Fahrenheit Scale-On a Fahrenheit thermometer, under standard atmospheric pressure, boiling point of water is 212 deg. and freezing point is 32 deg. above zero on its scale.

Fail Safe Control-Device which opens circuit when sensing element fails to operate.

Fan-A radial or axial flow device used for moving or producing artificial currents of air.

Farad-Unit of electrical capacity; capacity of a condenser which, when charged with one coulomb of electricity, gives difference of potential of one volt.

Faraday Experiment-Silver chloride absorbs ammonia when cool and releases ammonia when heated. This is basis on which some absorption refrigerators operate

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

File Card-Tool used to clean metal files.

Filter-Device for removing small particles from a fluid.

Flame Test For Leaks-Tool which is principally a torch and when an air-refrigerant mixture is fed to flame, this flame will change color in presence of heated copper.

Flapper Valve-The type of valve used in refrigeration compressors which allows gaseous refrigerants to flow in only one direction.

Flare-Copper tubing is often connected to parts of refrigerating system by use of flared fittings. These fittings require that the end of tube be expanded at about 45 deg. angle. This flare is firmly gripped by fittings to make a strong leakproof seal.

Flare Nut-Fitting used to clamp tubing flare against another fitting.

Flared Single Thickness Connection-Tube ending formed into 37 1/'2 deg. or 45 deg. bell mouth or flare.

Flash Gas-This is the instantaneous evaporation of some liquid refrigerant in evaporator which cools remaining liquid refrigerant to desired evaporation temperature.

Flash Point-Temperature at which an oil will give off 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 and a heavy electrical current is passed through the joint to be welded.

Float Valve-Type of valve which is operated by sphere or pan which floats on liquid surface and controls level of liquid.

Flooded System-Type of refrigerating system in which liquid refrigerant fills evaporator.

Flooded System, Low Side Float-Refrigerating system which has a low side float refrigerant control.

Flooding-Act of filling a space with a liquid.

Flow Meter-Instrument used to measure velocity or volume of fluid movement.

Flue-Gas or air passage which usually depends on natural convection to cause the combustion gases to flow through it. Forced convection may sometimes be used.

Fluid-Substance is a liquid or gaseous state; substance containing particles which move and change position without separation of the mass.

Fluid Coupling-Device which transmits drive energy to energy absorber through a fluid.

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

Flux-Brazing, Soldering-Substance applied to surfaces to be joined by brazing or soldering to free them from oxides and facilitate good joint.

Flux, Magnetic-Lines of force of a magnet.

Foam Leak Detector-A system of soap bubbles or special foaming liquids brushed over joints and connections to locate leaks.

Foaming-Formation of a foam in an oil refrigerant mixture due to rapid evaporation of refrigerant dissolved in the oil. This is most likely to occur when the compressor starts and the pressure is suddenly reduced.

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

Force-Force is accumulated pressure and is expressed in pounds. If the pressure is 10 psi on a plate of 10 sp. in. area, the force is 100 pounds.

Forced Convection-Movement of fluid by mechanical force such as fans or pumps.

Forced-Feed Oiling-A lubrication system which uses a pump to force oil to surfaces of moving parts.

Freezing Alarm-Device used in many freezers which sounds an alarm (bell or buzzer) when freezer temperature rises above safe limit.

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

Freeze-Up-1-The formation of ice in the refrigerant control device which may stop the flow of refrigerant into the evaporator. 2-Frost formation on a coil may stop the airflow through the coil.

Freezing-Change of state from liquid to solid.

Freezing Point-The temperature at which a liquid will solidify upon removal of heat. The freezing temperature for water is 32 F. at atmospheric pressure.

Freon-Trade name for a family of synthetic chemical refrigerants manufactured by DuPont De Nemours Inc.

Frost Back-Condition in which liquid refrigerant flows from evaporator into suction line; indicated by frost formation on suction line.

Frost Control, Automatic-A control which automatically cycles refrigerating system based on frost formation on evaporator.

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

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

Frost Free Refrigerator-A refrigerated cabinet which maintains the evaporator at frosting temperatures during all phases of cycle.

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

Fuse-Electrical safety device consisting of strip of fusible metal in circuit which melts when current is overloaded.

Fusible Plug-A plug or fitting made with a metal of a known low melting temperature, used as safety device to release pressures in case of fire.

Galvanic Action-Corrosion action between two metals of different electronic activity. The action is increased in the presence of moisture.

Gas-Vapor phase or state of a substance.

Gasket-A resilient or flexible material used between mating surfaces of refrigerating unit parts or of refrigerator doors to provide a leakproof seal.

Gasket, Foam-A joint sealing device made of rubber or plastic foam strips.

Gas-Noncondensible-A gas which will not form into a liquid under pressure-temperature conditions.

Gas Valve-Device for controlling flow of gas.

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

Gauge, High Pressure-Instrument for measuring pressures of range of 0 psig and 50 psig.

Gauge, Low Pressure-Instrument for measuring pressures or range of 0 psig and 500 psig.

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

Gauge, Vacuum-Instrument used to measure pressures below atmospheric pressure.

Grain-A unit of weight and equal to one 7000th of a pound. It is used to indicate the amount of moisture in the air.

Grille-An ornamental or louvered opening placed at the end of an air passageway.

Grommet-A plastic metal or rubber doughnut-shaped protector for wires or tubing as they pass through hole in object.

Ground Coil-A heat exchanger buried in the ground which may be used wither as an evaporator or as a condenser.

Ground, Short Circuit-A fault in an electrical circuit allowing electricity to flow into the metal parts of the structure.

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

Halide Refrigerants-Family of refrigerants containing halogen chemicals.

Halide Torch-Type of torch used to detect halogen refrigerant leaks.

Hastelloy-Trade name for a hard, noncorroding metal alloy.

Head Pressure-Pressure which exists in condensing side of refrigerating system.

Head Pressure Control-Pressure operated control which opens electrical circuit if high side pressure becomes excessive.

Head, Static-Pressure of fluid expressed in terms of height of column of the fluid, such as water or mercury.

Head, Velocity-In flowing fluid, height of fluid equivalent to its velocity pressure.

Heat-Form of energy the addition of which causes substances to rise in temperature; energy associated with random motion of molecules.

Heat Exchanger-Device used to transfer heat from a warm or hot surface to a cold or cooler surface. Evaporators and condensers are heat exchangers.

Heat Lag-When a substance is heated on one side, it takes time for the heat to travel through the substance. This time is called heat lag.

Heat Leakage-Flow of heat through a substance is called heat leakage.

Heat Load-Amount of heat, measured in Btu, which is removed during a period of 24 hours.

Heat Of Compression-Mechanical energy of pressure transformed into energy of heat.

Heat Of Fusion-The heat released in changing a substance from a liquid state to a solid state. The heat of fusion of ice is 144 Btu per pound.

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

Heat Pump-A compression cycle system used to supply heat to a temperature controlled space, which can also remove heat from the same space.

Heat Transfer-Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these three methods.

Heating Coil-A heat transfer device which releases heat.

Heating Control-Device which controls temperature of heat transfer unit which releases heat.

Heating Seasonal Performance Factor(HSPF)-the total heating output of a heat pump during its normal annual usage period for heating divided by the total electric power input in watt-hours during the same period.

Heating Value-Amount of heat which may be obtained by burning a fuel. It is usually expressed in Btu per pound or Btu per gallon.

Heavy Ends, Hydrocarbon Oils-The heavy molecules or larger molecules of hydrocarbon oils.

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

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

HG-(Mercury)-Heavy silver-white metallic element; only metal that is liquid at ordinary room temperature. Symbol, Hg.

High Pressure Cut-Out-Electrical control switch operated by the high side pressure which automatically opens electrical circuit if too high head pressure or condensing pressure is reached.

High Side-Parts of a refrigerating system which are under condensing or high side pressure.

High Side Float-Refrigerant control mechanism which controls the level of the liquid refrigerant in the high pressure side of mechanism.

High Vacuum Pump-Mechanism which can create vacuum in 1000 to 1 micron range.

Hi-Re-Li System-A patented heat pump cycle developed by Westinghouse Corp.

Hollow Tube Gasket-Sealing device made of rubber or plastic with tubular cross section.

Hone-Fine-grit stone used for precision sharpening.

Horsepower-A unit of power equal to 33,000 foot pounds of work per minute. One electrical horsepower equals 746 watts.

Hot Gas Bypass-Piping system in refrigerating unit which moves hot refrigerant gas from condenser into low pressure side.

Hot Gas Defrost-A defrosting system in which hot refrigerant has 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 Wire-A resistance wire in an electrical relay which expands when heated and contracts when cooled.

Humidifiers-Device used to add to and control the humidity in a confined space.

Humidistat-An electrical control which is operated by changing humidity.

Humidity-Moisture; dampness. Relative humidity is ratio of quantity of vapor present in air to greatest amount possible at given temperature.

Hydrolen-Tar-A hydrocarbon byproduct of oil industry. Used as a low melting temperature, waterproof sealing compound.

Hydrometer-Floating instrument used to measure specific gravity of a liquid. Specific gravity is ratio of weight of any volume of a substance to weight of equal volume of substance used as a standard.

Hydronic-Type of heating system which circulates a heated fluid, usually water, through baseboard coils. Circulating pump is usually controlled by a thermostat.

Hygrometer-An instrument used to measure degree of moisture in the atmosphere.

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

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