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A glossary, also known as an idioticon, vocabulary, or clavis, is an alphabetical list of terms in a particular domain of knowledge with the definitions for those terms. (wikipedia.org/wiki/Glossary)

Click on a letter of the alphabet to take you to the section containing words that start with that letter. For example, if you are looking for magnet, click on the 'M'. Read about magnets, and follow any links to animations, videos or other information.

"Ctrl + f" - you can also hold the "ctrl" and the "f" keys simultaneously. When the dialogue box appears in the top right hand corner, type the word you are looking for.

last updated 20 July 2017



Absolute pressure – Gauge pressure + atmospheric pressure. (Sometimes referred to with an “A” at the end – e.g. kPa A, Bar A, Psi A.)

Absorption Refrigeration – Absorption in chemistry is the taking up of one substance by another. Absorption refrigeration units work by using ammonia as the coolant, water and hydrogen gas to create a continuous cycle for the ammonia. These coolers typically have no moving parts, and generally run on propane or gas. Camping type fridges also operate on 12VDC or 240VAC to generate heat.

Absorption system JPEG

Animated absorption system GIF (Takes a few seconds to load).

Adiabatic cooling – Adiabatic cooling is the process of reducing heat through a change in air pressure caused by volume expansion.

AIRAH – Australian Institute of Refrigeration, Airconditioning and Heating: www.airah.org.au

Air Conditioning – the science of maintaining internal conditions regardless of external conditions: temperature, humidity, air quality and air movement. View the "room temperature room" video.

Kybom Air Conditioning Manufacturer Homepage.

Alternator – electromechanical device that turns mechanical energy into alternating current (AC) electricity.

Alternating current (AC) – current repeatedly changes direction of flow.

Ammeter – device used to measure current flow. (See Amp).

Ammeter Click for a larger image

Ammonia (R717) – R717 is refrigerant grade high purity ammonia (NH3)(natural Refrigerant) that has zero ODP and zero GWP. The product typically is 99.98% pure with minimal levels of moisture and other impurities (> 200 ppm and > 5 ppm Oil) making it ideal for use in all types of refrigeration systems.

(Linde R717 Brochure). Click for a larger image

Amp (A) – Ampere is the unit of electric current. (See ammeter)

Anemometer (Rotating Vane and hotwire) – device for measuring the speed of airflow in the atmosphere, ductwork and in other gas-flow applications

1. Rotating Vane anemometer image

Anneal (Annealing) – is a heat process whereby a metal is heated to a specific temperature or colour and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily. Copper tube is heated to a red heat and allowed to cool slowly.

1. Annealing Video.

ASHRAE – American Society of Heating, Refrigeration, and AIr Conditioning Engineers. www.ashrae.org

Australian Refrigeration Association (ARA) – , a non-profit association comprised of people and organisations that support our objectives particularly from a design, engineering and operating point of view. http://www.ausref.org.au/

Australian Refrigeration Council Ltd (ARC) – administers refrigerant handling licences and refrigerant trading authorisations on behalf of the Australian Government. http://www.arctick.org/index.php

Automatic Expansion Valve (AEV) – developed for small cooling units where the load is reasonably constant, such as room air conditioners, domestic refrigerators, drink dispensers, food dispensers, ice cream cabinets bottle coolers, home freezers, ice cube makers, ice cream freezers and milk coolers.

Automatic Expansion Valve (AEV) cutaway image by Hermawan

Automatic Expansion Valve (AEV) cutaway image by http://neilorme.com/AEV.shtml

Armature – generally relates to a movable piece of ferromagnetic metal placed between poles of a magnet. For example, the rotating core of an electric motor or alternator, or the moving arm of a relay.

Atmospheric Pressure – is the pressure exerted by the weight of the air above us due to gravity. At sea level, atomspheric pressure is taken as 101,325 pascals or 101.3 kPa (14.7 psig) and can also written as 29.92 " Hg.

Atom – the smallest part of an element that can exist.


Azeotrope – A blend made up of two or more refrigerants with similar boiling points that act as a single fluid. The components of azeotropic mixtures will not separate under normal operating conditions and can be charged as a vapor or liquid. (R500 series refrigerants)


Balometer (flow hood) – directly reads average air flow rate, either intake or outflow, at ceiling, wall or floor diffusers.

1. Flow Hood - image

2. Flow Hood to measure register air flow. - image

Battery – a collection of cells connected together to deliver direct current (DC). Different methods of connection determine the voltage and the size of cells determines available current.

Bell Jar – A bell jar is a piece of laboratory equipment used for creating vacuums. A bell jar is placed on a base which is vented to a hose fitting, which can be connected via a hose to a Vacuum Pump.  Bell Jar video.  

Boiling Point

Water boiling at room temperature video

Bell Jar video.  

Bourdon (tube) Gauge – Bourdon pressure gauge uses the principle that a flattened tube tends to change to be straightened or larger circular cross-section when pressurized. (http://en.wikipedia.org/wiki/Pressure_measurement#Bourdon).

1. Danfoss bourdon tube animation

2. Low side compound gauge

Brazing (Silver Soldering) – metal-joining process whereby a filler metal is heated above melting point and distributed between two or more close-fitting parts by capillary action. Read the Kembla brazing manual here.

Bubble Point – the temperature at which liquid refrigerant begins to bubble when the saturation point is reached. (The lowest boilng point of one of the refrigerants in a zeotropic blend).

Temperature glide image showing bubble and dew point.

Building Management System (BMS) – A BMS is a computer based graphical interface and control system for large installations. A system for centralizing and optimizing the monitoring, operating, and managing of a building. Services may include heating, cooling, ventilation, lighting, security, and energy management.

Bundy Tube – Bundy tube, sometimes called Bundy pipe, is type of double-walled low-carbon black steel tube used for domestic air cooled static condensers.

1. Domestic fridge bundy tube static condenser. (Image)



Calipers – an instrument for measuring external or internal dimensions, or for marking out.

1. Types of Calipers (PDF)

Capacitance – the ability of a device to store an electrical charge.

Capacitor – a device capable of storing an electrical charge.

1. Capacitor Video

2. What is a capacitor? PDF

Capacitor - Run: Runs capacitors are rated in a range of 2-80 microfarad (mfd). Run capacitors are also rated by voltage classification. The voltage classifications are 370V 440V and 480V. Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding. This is why sizing is so critical. If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.(source:Louisiana State University)

Capacitor - Start. – Start capacitors are housed in a black plastic case and have a mfd range as opposed to a specific mfd rating on run capacitors. Start capacitors (ratings of 80 microfarad or higher) have three voltage classifications: 125V, 250V, and 330V. Examples would be a 35 mfd at 370V run capacitor and an 88-108 mfd at 250V start capacitor. Start capacitors increase motor starting torque and allow a motor to be cycled on and off rapidly. Start capacitors are designed for momentary use. Start capacitors stay energized long enough to rapidly bring the motor to 3/4 of full speed and are then taken out of the circuit. (source:Louisiana State University)

Capacity control (Compressor, Evaporator, Condenser) – Matching the performance of the system to load or conditions in the controlled space is achieved with capacity control - compensates for low load and low ambient conditions.

1. Capacity Control of compressors (Word Doc)

Capillary (Tube) – a refrigerant metering device. Capillary is copper tube of very small internal diameter - ranging from 0.5 to 2.28 mm (0.020 to 0.09 inches). Capillary tube is commonly used as the throttling device in the domestic refrigerators, deep freezers, water coolers and air conditioners.

1. NNR029 Capillary Systems Student Book. (superseded TAFE NSW resource). .

2. Supco Capillary Manual

Capstone (UEENEEJ109A) – This unit covers testing and visual inspection for verifying that a refrigeration and air conditioning system and components are safe, comply with requirements and functions as intended. It encompasses working safely, conducting compliance tests, conducting visual inspections, identifying non-compliance defects and mandatory reporting requirements. Student Guide

Carbon Dioxide (CO2) – a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. The combustion of all carbon-containing fuels, such as methane (natural gas), petroleum distillates (gasoline, diesel, kerosene, propane), but also of coal and wood, will yield carbon dioxide. Carbon dioxide is used as 'dry ice', and as a refrigerant (R744). Carbon dioxide Wiki Page

Carbon Dioxide (CO2) Refrigerant (R744) – Non-toxic, Non-flammable, Non-ozone-depleting, Environmentally friendly, with a Global Warming Potential = 1. A high pressure refrigerant used in commercial and industrial refrigeration applications:

R744 Website www.r744.com

CO2 Phase Changes - Danfoss Video large (35 MB)

Bitzer sub-critical animation - Bitzer CO2 System

Tube system for high-pressure applications (PDF) - High-strength copper alloy Wieland K65

Cascade System: Arrangement in which two or more refrigeration systems are used in series. The evaporator of one machine is used to cool the condenser of another. These are used in ultra low temperatures.

CFC (ChloroFluoroCarbon) Refrigerant – CFC refers to the chemical composition of the refrigerant. ChloroFluoroCarbon indicates that the refrigerant is comprised of Chlorine, Fluorine, and Carbon. Common CFC refrigerants are R11, R12, R13, R113, R114, and R115. These refrigerants have been phased out of use because of their high ozone depletion potential (ODP).

Celsius Scale – a temperature scale (°C) that was developed by Anders Celsius in 1742. The zero point of the Celsius scale is set to the temperature at which water freezes, and 100 is the temperature at which water boils (at atmospheric pressure). The Celsius scale is the standard scale used around most of the world to measure air temperatures. The United States uses the Fahrenheit scale (°F).

Checklist – helps to ensure consistency and completeness in carrying out a task. Sample installation and commissioning checklist spreadsheet.

Chiller (Air Conditioning) – See "water chiller".

Circuit – the configuration of an electrical source, conductors and devices, in order to be capable of carrying current.

Circuit Breaker – is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent/overload or short circuit.

Image   Click for animation

Circuit Breaker Trip Animation video

Coldrooms (Freezer Rooms)Coldrooms and merchandising cabinets

1. Coldrooms panels and construction

Compression Ratio –The compression ratio is the ratio of the absolute discharge pressure (kPaA) to absolute suction pressure (kPaA), found using the formula Discharge Pressure Absolute ÷ Suction Pressure Absolute. Suction pressure has great influence has on compression ratio. A change in head pressure does not influence the compression ratio as much as suction pressure. High compression ratios are a major reason systems run hot. There are other reasons a system can exhibit high discharge temperatures, but knowing how to find the compression ratio can greatly aid a service technician in discovering what is wrong with a troublesome system.

Compressor (refrigerant) – the refrigeration compressor circulates refrigerant in the vapour compression system, and increases the pressure and temperature of the refrigerant so that it can be condensed into liquid. The compressor separates the low and high sides of the system.

1. Tecumseh compressor motor and component information. (PDF)

2. Screw compressor animation.

3. Bizer Screw compressor animation.

4. Copeland Scroll compressor animation.

5. Copeland Digital Scroll compressor animation.

6. Danfoss Centrifugal compressor video

7. Rotary compressor animation.

8. Danfoss Reciprocating compressor video.

9. York Screw compressor animation .exe (3.2MB)

Condensate (condensation) – waste water from the condensation formed on the evaporator in refrigeration processes. Condensate drains need to be correctly designed and installed to facilitate correct drainiage. View an image of a drain installation here. Use an Ezi-trap to facilitate cleaning and inspection.

Condenser – A heat exchanger used to reject refrigeration system heat to the cooling medium (ambient air or water).

1. Condenser animation image

2. Tube in tube condenser image (300 Kb)

Condenser pressure regulator (CPR) – maintains minimum condensing pressure in low ambient conditions.

Danfoss CPR animation

Conductance – the opposite of resistance, relates to the ease with which electricity will pass through material.

Conductor – material that electricity will flow through with little resistance.

Contactors – an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.A contactor is controlled by a circuit which has a much lower power level than the switched circuit.


Cooling load temperature difference (CLTD) calculation method The CLTD/CLF/SCL (cooling load temperature difference/cooling load factor/solar cooling load factor) cooling load calculation method was first introduced in the 1979 ASHRAE Cooling and Heating Load Manual and is regarded as a reasonably accurate approximation of the total heat gains through a building envelope for the purposes of sizing HVAC equipment. Error when using the CLTD/CLF/SCL method tends to be less than twenty percent over and less than ten percent under.


Cooling Tower transfer waste heat from the condenser to the atmosphere. Cooling towers use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature. 

1. Cooling tower best practice guidelines (AIRAH)

2. Cooling tower types (AIRAH)

3. My Cooling Tower .com.au (AIRAH)

COP (Coefficient of Performance) – the ratio of the refrigerant effect (refrigeration capacity) to the work done by the compressor - the higher the number, the more efficient the system.

Coulomb – practical unit of an electrical charge. The quantity of electric charge transferred each second by a current of one ampere.

Crankcase Pressure Regulator (CPR) – An outlet pressure regulator which maintains a predetermined maximum outlet pressure. Designed to prevent compressor motor overload. Commonly used on low temp systems to protect the compressor from high back pressure after a defrost.

To limit the input pressure in the compressor, obtain the compressor manufacturer's specifications for the maximum suction pressure allowed for the refrigerant and the temperature. Configure the valve 20 - 30 KPa below the maximum pressure. An alternative method is to use an ammeter on opening the valve to configure a reference point that does not exceed the maximum amperage (RLA) for the compressor (90% of amps in winter).

Critical Point (Critical temperature) – the temperature above which gas cannot be liquefied, irrespective of pressure. Conventional refrigeration cycles can only operate efficiently using fluids well below critical temperature.

1. Critical temperature webpage - courtesy Purdue University Department of Chemistry

Critical Pressure – the saturation pressure equivalent to the Critical Temperature.

Current (I) – the movement or flow of electrons along a conductor. The symbol for current is I and the unit of measure is amps (A).

Current Relay – Current starting relays are used to start single-phase, refrigeration motors requiring low starting torque. Current relays are often used with capillary tubes. (Pressures equalize on the off cycle).

1. Current Relay image by Hermawan


Defrost (timer) – An electro-mechanical, or digital clock device that periodically switches from cooling to defrost to remove the buildup of frost from the evaporator. Typically 4 defrosts per day at 6 hour intervals with a duration of approximately 20 -30 minutes. Types include:

  • 1. Time initiated, time terminated,
  • 2. Time initiated, temperature terminated,
  • 3. Time initiated, pressure terminated, and
  • 4. Electronic (Carel, Dixell, phasefale etc).

1. Paragon defrost timer PDF

2. Domestic defrost 6 hour timer - image

3. Defrost termination klixon - animated GIF image

Delta connection (windings) – The connection of a three phase motor in the Delta configuration, often used with a star/delta starter.

1. Star - Delta Starter (PDF)

2. Star - Connection Starter (PDF)

3. Delta - Connection (PDF)

Diameter – the distance from one side of a circle to the other; the symbol is a circle with a line through it (ø).

Differential Pressure Switch – a switch that compares two pressures often used to verify fluid flow: chilled water, compressor oil, air.

1. Emerson oil pressure switches - copeland: technical information guide.

Diode – a semi-conductor device that allows current flow in one direction only.

Direct current (DC) – current that flows in one direction only.

1. Direct current (DC)– DC tool kit - animated circuit construction. (2MB)

Distributor (Refrigerant) –function of the refrigerant distributor is to equally distribute refrigerant flow from the thermostatic expansion valve into each circuit of a multi-circuit evaporator coil. (Requires an externally equalised TX valve).

Sporlan Distributor Fact sheet (PDF)

Domestic Refrigerator (Fridge) – A refrigerator or fridge is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Refrigeration is an essential food storage technique where low temperatures lowers the reproduction rate of bacteria, so the refrigerator reduces the rate of spoilage. Fridge - +2 to + 4 Deg C, Freezer - -18 Deg C.

1. Domestic Fridge - Video (13 Mb)

2. Domestic Fridge Compressor - Video (25 Mb)

3. How not to carry a fridge - Video (1.5 Mb)

Drier (dryer) – liquid line, suction line and suction burnout. A filter-drier in a refrigeration or air conditioning system has two essential functions: one, to adsorb system contaminants, such as water, which can create acids, and two, to provide physical filtration.

1. Drier exposed video (Aussie 50 you tube channel)

2. Drier exposed Image

3. Copper spun Drier exposed Image


EC Motor – brushless DC motors which include in-built electronics to convert the AC supply to DC without the need for a separate DC supply. EC fans provide a more efficient (up to 30%) means of airflow with the additional benefit of variable speed control via an output signal from the unit controller.

EER – Energy Efficiency Ratio (EER) is a measure of system efficiency at a given set of rating conditions. It is a ratio calculated by dividing the cooling capacity in kW by the power input in kW.

Efficiency – the efficiency of an electrical machine can be determined by comparing the input power against the output power.

Electrode – a conductor where current passes from a solid into a liquid, into a gas, or into a vacuum, or vice versa.

Electrolysis – chemical change to material as a result of the passage of an electric current through an electrolyte.

Electrolyte – a conducting substance or medium, eg acid, base or salt, in which the flow of current is accompanied by the movement of matter in the form of ions.

Electromagnet – a magnet that is created by passing electrical current through a coil wound around an iron core.

Electromotive force (EMF) – voltage between the terminals of a cell or generator in the open circuit condition.

Electron – negatively charged particle of an atom.

Electronic Expansion valve (ETX or LEV) – electronically controlled needle and seat metering device used in large split air conditioning systems..

1. Electronic Expansion valve (video) - Aussie 50 YouTube channel.

2. Sporlan Electronic Expansion valve (PDF 2.38 Mb)

Energy Recovery (also see recovery heat wheel and heat exchanger) – a heat recovery wheel is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the heat energy. For example; using toilet or kitchen exhaust air to cool down fresh outside air.

1. Watch rotating recovery wheel video

2. Rotary wheel Animation

3. Plate heat exchanger animation.

Engineering Notation – version of scientific notation in which the powers of ten must be multiples of three.


472,690,128,340 = 472.690128340 × 109

0.000 063 8 = 63.8 × 10–6

Enthalpy – the thermodynamic property of a substance defined as its total internal energy plus the total heat & heat content Pv/J. Sometimes called total heat and heat content.

Pressure Enthalpy Explained PDF

Entropy – The rate at which heat is absorbed into an object.

Evacuation – Using a vacuum pump, evacuating a refrigeration system serves two primary objectives:

  1. It removes noncondensables (air, nitrogen etc)
  2. It dehydrates (removes water vapor)
  3. Evacuation & Dehydration Videos

1. Introduction to Evacuation

2. Evacuation Safety

3. Evacuation - the right pump

4. Evacuation - the right tools

5. Evacuation & Charge

6. Evacuation pump maintenance

7. Evacuation pump features

Evaporative Cooler (swampy) – evaporative air coolers use the effect of "Latent Heat" to cool the air as it passes over a watersoaked porous material. The amount of cooling of the air depends entirely upon the amount of moisture already in the air so they are more effective in dry air in inland areas. Because of the increase in relative humidity as air is cooled and moisture added, air should never be recirculated through an evaporative cooler. To be effective, only fresh outside air should be brought through to cooler, and be exhausted out through the other sides of the conditioned space.

1. Evap cooler diagram.

2. Evap cooler image 1

3. Roof top Evap cooler image 2

Evaporator – A heat exchanger where heat from the refrigerated space is absorbed by the refrigerant (using latent heat of vapourisation), to maintain temperature and humidity at desired conditions.

1. Wall split Evaporator cutaway image (Hermawan).

2. Operating Evaporator - note the change in refrigerant quality from the TX valve to the bulb.


Evaporator Pressure Regulator (EPR) – installed in the suction line after the evaporator to regulate the evaporating pressure in refrigeration systems with one or more evaporators and one compressor. In such refrigeration systems (operating on different evaporating pressures) the EPR is installed after the evaporator with the highest evaporating pressure.

1. Danfoss EPR animation.

2. Sporlan EPR PDF

Exam Technique – open the PDF document for hints, tips and tricks to do better in assessments.

Exam Hint sheet (PDF)

Expansion (metering)Device – meters liquid into the evaporator at the same rate which it is being vaporized and it maintains a pressure difference between the high and low sides of the system.

1. Types of metering devices - image

2. Hand expansion valve

3. Automatic Expansion Valve (AEV) cutaway image by Hermawan

3 a Automatic Expansion Valve (AEV) cutaway image by http://neilorme.com/AEV.shtml

4. High side float (HSF)

5. Low side float (LSF)

6. Fixed orifice (accurator)

7. EEV (electronic expansion valve)

8. Thermal Expansion (TX) Valve



FanAxial FanAn apparatus with rotating vanes or blades that creates a current of air for cooling, heating, or ventilation. Types of fan include: Axial (propellar, tube or vane axial), centrifugal (forward, radial, backward and airfoil), and crossflow (wall splits).

1. Centifugal Fan image 1

1a. Centifugal Fan image 2

1b. Centifugal Fan animated video

1c. Centifugal Fan animation

2. Cross flow barrel fan image

3. Propellar fan image

4. Axial flow fan image

5. FanTech Axial fan installation dos and don'ts (PDF)

6. Engineering Handbook on Fans PDF)

7. Centrifugal fan types (BMP)

Farad (F) – derived unit of measure for capacity that exists between two plates of a capacitor if the transfer of one coulomb from one plate to the other creates a potential difference of one volt.

Faraday's Law Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generatorstransformersinduction motorselectric motorssynchronous motors, and solenoids.

1. Faraday's Law Animation

2. Faraday's Law Animation (GIF)

Fasteners (screw, Bolt, Nut) – a hardware device that mechanically joins or affixes two or more objects together.

1. Table of Fasteners PDF (400 Kb)

F-Gas – Fluorinated gases (‘F-gases’) are a family of synthetic (man-made) gases used in a range of air conditioning and refrigeration applications.

F-Gas regulation – EU regulation introduced into European Law in 2007. Impacts the use of fluorine based refrigerants. Regulation leads to record keeping, leak detection and competence levels for engineers. See F Gas Compliance.

Field – a region where magnetic lines of force can be detected from a magnet or electrical circuit.

Filter – fibrous (or other) materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. They are usually located in the return air path and also assist in keeping the evaporator coil clean. Types: viscous, HEPA, dry and electrostatic.

1. Filtertech filter types catalogue PDF 5 MB

2. Filter pressure drop (when to replace filters) PDF

3. Filter types (AC) PDF 2.5 MB

4. HEPA (High efficiency particulate arrestance) Filter image

5. HEPA Filter image 2

Flexible cable (lead) – specially designed to cope with the tight bending radii and physical stress associated with moving and vibration. Used in the HVAC industry for fan motors, compressors and controls.

Fluorocarbon – A hydrocarbon in which some or all of the hydrogen atoms have been replaced by fluorine..

Fluorocarbon refrigerant – A refrigerant consisting of or containing flurocarbon.

Flow hood (Balometer) – directly reads average air flow rate, either intake or outflow, at ceiling, wall or floor diffusers.

1. Flow Hood - image

2. Flow Hood to measure register air flow. - image

Free electron – an electron that is not bound to any particular atom and can therefore move from atom to atom in a conductor.

Frequency – the number of times per second that something changes. Relates to alternating current in particular and is measured in hertz (Hz).

Full Load Amps (FLA) – FLA is the nameplate amperage rating of the motor when it is running at its designed horsepower and on the motors designed voltage.


Galvanometer – device for measuring or detecting small amounts of current.

Galvanised – protective coating on iron to prevent rust, achieved by the use of a galvanic current or zinc coating.

Gauge Pressure – (see refrigeration gauges) The reading taken from a gauge normally zeroed at atmospheric pressure (one bar absolute or 14.7 psi) so that pressures can be also be read as a negative when below atmospheric pressure. (Often referred to with “G” on end – e.g. kPaG, BarG, PsiG).

Global Warming – is the term used to describe a gradual increase in the average temperature of the Earth's atmosphere and its oceans, a change that is believed to be permanently changing the Earth's climate.

Global Average Temperatures Graphic Animation

GWPGlobal (Greenhouse) Warming Potential. It compares the amount of heat trapped by a certain mass of a refrigerant to the amount of heat trapped by a similar mass of carbon dioxide; (CO2 =1).


HCFC (HydroChloro-Fluoro-Carbon) Refrigerant – HCFC refers to the chemical composition of the refrigerant. HydroChloro-Fluoro-Carbon indicates that the refrigerant is comprised of Hydrogen, Chlorine, Fluorine, and Carbon. Common HCFC refrigerants are R22.

Heat Exchange – a device designed to efficiently transfer or "exchange" heat from one substance to another. For example, condenser and evaporator, or car radiator. Energy recovery wheels use heat exchange to reduce energy losses by recovering waster heating or cooling.

1. Watch rotating recovery wheel video

2. Rotary wheel Animation

3. Plate heat exchanger animation.

Heat Pump (reverse cycle air-con) – A heat pump is a HVAC unit that heats or cools by moving heat. During the winter, the indoor coil becomes the condenser and circulates warm air through the conditioned space. In the summer, it reverses the process and the indoor unit is an evaporator that removes heat from your house and releases it outdoors. View the heat pump page.

Hermawan – Likes to share his knowledge, experience and ideas. Click on the icons to check out his Facebook Page and Blog page.

Hermawan Facebook Hermawan Facebook

HFC (HydroFluoroCarbon) Refrigerant – HFC refers to the chemical composition of the refrigerant. HydroFluoroCarbon indicates that the refrigerant is comprised of Hydrogen, Fluorine, and Carbon. Common HFC refrigerants are R134a.

HFO (hydrofluoro-olefin) – designed for automotive AC, HFO refrigerants have a very low GWP, and are the fourth generation of refrigerants to be developed.

1. HFO 1234yf (PDF)

Henry (H) – unit of measure of inductance. If the rate of change of current in a circuit is one ampere per second, and the resulting electromotive force is one volt, then the inductance of the circuit is one henry.

Heritage listing – Buildings of natural or historical significance that are registered with the Environmental Protection Agency (EPA) or Department of Environment and Heritage Protection (Different in each state and territory).

Hertz (Hz) – unit of measure of frequency, one hertz (Hz) equals once per second.

Humidity (also see Relative Humidity) – is the amount of water vapor in the air. There are three main measurements of humidity: absolute, relative and specific.

Absolute humidity is the water content of air at a given temperature expressed in gram per cubic metre.

Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum (highest point) for that temperature.

Specific humidity is a ratio of the water vapor content of the mixture to the total air content on a mass basis.

HVAC & R – pronounced either "H-V-A-C" or "H-vak") is an acronym that stands for "Heating, Ventilation, and Air conditioning". HVAC is sometimes referred to as climate control, and air movement, humidity and temperature must all be closely regulated to maintain comfortable, safe and healthy conditions within an occupied space.

Hydrocarbon (HC) – are naturally occurring, organic compounds consisting of hydrogen and carbon atoms. As a refrigerant, they are non-toxic, have no ozone depleting properties and almost zero global warming potential. (R290 propane, and R600a isobutane, are two common refrigerants in use).

Hydrocarbon page.

Hygroscopic – A tendency for refrigeration and vacuum pump oils, refrigerants, and driers to absorb moisture from the atmosphere or refrigeration system.


Insulation (pipe) – material that is highly resistive to conducting heat - flexible, closed cell, elastomeric, nitrile rubber insulation that offers reliable protection against condensation and effectively prevents energy loss. (Armaflex Website).

1. Insulation Installation Manual (pdf 2MB). Isopipe Website.

Insulator – material that is highly resistive to conducting electricity.

Ion – atom or molecule that has become electrically charged by either gaining or losing electrons.

Isometric – (isometric projection) a three-dimensional drawing with horizontal edges of the object drawn usually at a 30° angle and all verticals projected perpendicularly from a horizontal base; all lines are drawn to scale.

Impedance – the opposition that is present in a circuit to the passage of alternating current. The symbol for impedance is Z; it is measured in ohms.

Inductance – relates to the characteristic of a circuit to have a voltage induced into it by current variation within the circuit itself (self-inductance) or from a nearby circuit (mutual-inductance). The henry (H) is the unit of measure for inductance.

Inverter – an electrical device that converts direct current (DC) into alternating current (AC).


Joule (J) – the unit of work or energy. It is equal to one watt for one second.


Kelvin (K) International System (SI) unit of temperature.

Klixon – A trade name for a bimetallic switch used to protect other devices. The Klixon, or 'thermal overload' is a temperature-sensitive electrical switch that opens when a certain temperature is exceeded, or excess current is drawn.

Klixon operation animation GIF

Kybom Airconditioning – Kybom Refrigeration and Air Conditioning Co., Ltd.is a technology and quality oriented Company, and is a leading supplier to the air conditioning industry.

Kybom Air Conditioning Manufacturer Homepage.

Fan Coil Factory images (PDF)

Water cooled R410A Heat Pump Brochure(PDF)

Air Handling Unit Brochure (PDF)

Fan Coil Unit Brochure (PDF)

Package Unit Brochure (PDF)

Water Cooled Screw Chiller Brochure (PDF)

Fan coil manufacture - Video


Leak detection – methods of finding leaks in referation systems - for all types of primary refrigerants:

  • (a) liquid submersion testing - pressurise and submerse a component in liquid (water bath). Bubble indicate the location of a leak.

  • (b) foam enhancer leak detection - soapy water or 'big blue': Spray on bubble type leak detection fluids allow accurate pin pointing of leaks as the user can watch bubbles or foam actively brew at the point of leakage.

  • (c) positive pressure holding test / pressure drop off test (gross leaks only)

  • (d) vacuum degradation test (gross leaks only) - the difference in pressure between a vacuum and atmosphere is only 101.3 kPa. The vacuum degradation method is only reliable for large leaks - missing schraeder core, missed weld, fractured pipe, loose flare nut etc.

  • (e) fluorescent leak detection - UV dye is added to the system and if a leak occurs a small amount of the UV dye which is carried with the oil is deposited at the leak site, this dye can be seen using UV lights.

  • (f) electronic leak testing (ultrasonic) - Ultrasonic sound is a range of sound (20kHz) that is above the human hearing capacity. Turbulence created by air or a gas forced through a small orifice generates ultrasonic sound. Ultrasonic leak detection is an ideal method to located leaks in systems pressurised with dry nitrogen.

  • (g) electronic leak testing (electronic) - A good electronic leak detector will have equal sensitivity to CFCs, HCFC's, and HFC's.

  • (h) mass spectrometer - Sensitive mass spectrometer measuring equipment detects helium and proves the system has a leak. See 'mass spectrometer'

  • (i) sulpur candle - when lit, a sulfur candle will give off a very thick, white smoke when it contacts the ammonia leak.

  • (j) Phenolphthalein paper - where the moistened paper will turn pink (small amount) or scarlet (bigger amount) when in contact with this ammonia gas.

  • (k) Litmus paper - moistened red litmus paper turns blue in the presence of ammonia gas.

Leak Detection

Yellow Jacket Electronic Leak Detectors Video

Real Skills Europe guide to good leak testing PDF

Legislation – relates to law and includes Acts, Ordinances, Regulations and other forms of delegated legislation such as rules and bylaws.

Legionella – a pathogenic group of gram negative bacteria, that includes the species L. pneumophila, causing Legionellosis (all illnesses caused by Legionella) including a pneumonia type illness called Legionnaires Disease and a mild flu like illness called Pontiac fever.

Lethal concentration 50 (LC50) – LC values usually refer to the concentration of a chemical (like refrigerant) in air. According to the OECD (Organisation for Economic Cooperation and Development) Guidelines for the Testing of Chemicals, a traditional experiment involves groups of animals (Rats?) exposed to a concentration (or series of concentrations) for a set period of time (usually 4 hours). The animals are clinically observed for up to 14 days. The concentrations of the chemical in air that kills 50% of the test animals during the observation period is the LC50 value. Other durations of exposure (versus the traditional 4 hours) may apply depending on specific laws.

Class A signifies refrigerants with an LC50 ≥ 10,000 ppm.

Class B signifies refrigerants with an LC50 > 10,000 ppm..

Liquid line receiver – (Vertical or horizontal) located after the condenser in refrigeration and air conditioning systems, the function of a Liquid Refrigerant Receiver is to:

1. Store liquid refrigerant to ensure 100% liquid flows to the expansion device, and

2. Provide storage for the refrigerant charge during system service or maintenance, pump down cycle or low load conditions.

Liquid Line receiver Image

Liquid line solenoid valve (LLSV) – a direct operated solenoid valve commonly used on pump down systems.

1. Direct operated solenoid valve - Danfoss animation

2. Pilot operated solenoid valve - Danfoss animation

3. Solenoid valve - Cutaway image courtesy Hermawan

Load – a device, appliance or component in an electrical circuit that performs work and therefore consumes energy, eg lamp, motor, etc.

Locked Rotor Amps (LRA) – "Locked Rotor Current" also called LRA which stands for Locked Rotor Amps, is commonly found on electric motor nameplates. Locked Rotor essentially means the motor is not turning. The current or amps in this case have to do with the amount of electrical energy required to start the motor. At the instant the motor is switched on, it is not turning, and draws the maximum current. .

Low pressure control (LP) – a control circuit electrical switch operated by the low pressure side of the system as either a safety control or for pump down. Cut out = Cut In - Differential.

1. LPC setting image by Hermawan

2. TD & LP/HP settings cheat sheet (PDF)

3. Danfoss LP control Animation


Magnehelic – Brand name of a gauge designed to measure pressure drop - typically across air conditioning filters.

Image 1

Image 2

Magnetic – refers to the invisible magnetic field that surrounds a magnet or electromagnet.

Magnetic Contactors – an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.A contactor is controlled by a circuit which has a much lower power level than the switched circuit.


Manometer – may be any device that measures pressure. However, unless otherwise qualified, the term "manometer" most often refers specifically to a U-shaped tube filled with fluid.

Mass Spectrometer – a highly sensitive method of leak detection in refrigeration systems. A vacuum is pulled on the equipment, and then helium is sprayed over the area that potentially has a leak. Sensitive mass spectrometer mesuring equipment detects helium and proves the system has a leak. Read more about the Mass spectrometer here.

Metering (expansion) Device – meters liquid into the evaporator at the same rate which it is being vaporized and it maintains a pressure difference between the high and low sides of the system.

1. Types of metering devices - image

2. Hand expansion valve

3. Automatic Expansion Valve (AEV) cutaway image by Hermawan

3 a Automatic Expansion Valve (AEV) cutaway image by http://neilorme.com/AEV.shtml

4. High side float (HSF)

5. Low side float (LSF)

6. Fixed orifice (accurator)

7. Electronic Expansion valve (ETX or LEV) – Electronic Expansion valve (video) - Aussie 50 YouTube channel.

8. Thermal Expansion (TX) Valve

Metre (m) International System (SI) unit of length. Since 1983, the metre has been internationally defined as the distance travelled by light in a vacuum during a time interval of 1/ 299 792 458 of a second.

Micron – A micron is a metric measure and is defined as 1 millionth of a meter or 1 thousandth of a millimeter. The micron then is a much more precise method for measuring a deep vacuum

Motor (induction or asynchronous) – motor is an AC electric motor in which the electric current in the rotor needed to produce torque is induced by electromagnetic induction from the magnetic field of the stator winding. An induction motor's rotor can be either wound type or squirrel-cage type.

1. Exploded View of an induction motor

2. Cutaway View of an induction motor

3. Video - how an induction motor works. (6 MB)

4. Best Practice guide - motors (PDF)

Motor starters – Starting is a process where a motor's rotor is brought from zero speed to rated (or desired) speed. Motor starters can limit start current, control torque and protect the electrical circuit from overloading in fault conditions.

1. Single Phase motor starters wiring diagram image - PTC relay, current relay & potential relay: (Image by Hermawan).

2. DOL three phase motor starter wiring diagram: ( JPG Image by Hermawan)

3. Potential relay video. ( 25 MB).

4. ABB Soft Starter Handbook PDF. (8 MB).

5. Three Phase motors start schematics (PDF)

6. Three Phase motors start schematics (PDF) downloaded from http://www.sari-energy.org/

7. 3 phase motor starters animated schematic video: DOL, contactor DOL, Star Delta, Autotransformer, primary resistance and secondary resistance. (Video 11.5 MB)

Multimeter – electrical meter that is capable of measuring a range of different electrical values, (Ohms, Volts and Amps).


Natural refrigerants – naturally occurring substances such as; hydrocarbons (propane, iso-butane), CO2, ammonia, water and air. Natural refrigerants are heat transfer mediums in refrigerators and air conditioners that do not harm the ozone layer, and have little or no effect on climate change. http://www.refrigerantsnaturally.com/natural-refrigerants/about-natural-refrigerants.htm

1. Natural refrigerant types JPG image courtesy 'refrigerantsnaturally.com'

Negative Temperature Co-efficient (NTC) – a type of variable resistor used to measure temperature in the HVAC&R industry. As the temperature increases, the probes resistance decreases (and vice versa). The correct resistance value for any probe must be read from the manufacturer's data table.

1. NTC Probe application guide - PDF

Neutron – neutral (uncharged) particle of an atom found in all atoms except hydrogen.

Newton (N)International System (SI) unit of force.

Nitrogen (N) – colourless, odourless inert gas that forms about 78 per cent of the earth's atmosphere. Liquid nitrogen (made by distilling liquid air) boils at 77.4 kelvins (−195.8°C) and is used as a coolant, and pressure testing HVAC & R systems prior to refrigerant charging.


ODPOzone Depletion Potential - The capacity of a refrigerant to destroy stratospheric ozone. ODP is stated relative to the ODP of CFC-11, which is taken as having an ODP of 1.

ODSOzone Depleting Substance - are those substances which deplete the ozone layer and are widely used in refrigerators, airconditioners, fire extinguishers, in dry cleaning, as solvents for cleaning, electronic equipment and as agricultural fumigants.

Ohm (Ω) – derived unit for measurement of resistance. If a device dissipates one watt of power with one ampere of current flowing through, it has a resistance of one ohm (R = P/I2).

Ohm's Law (Ω) – states that the current through a conductor between two points is directly proportional to the potential difference across the two points. V = I x R.

1. Ohm's law animation (JAR file)

Ohms Law Power Wheel

Ohm's Law

Ohmmeter – a device used for measuring resistance in ohms.

Oil (Refrigerant) – See refrigeration oil

Oil Trap – Pipe work designed to trap refrigerant oil so that it is returned to the compressor.

1. Oil Trap image (Hermawan)

2. Double Riser (Hermawan)

3. Wall Split oil trap (indoor above outdoor) (Hermawan)

4. Wall Split oil trap (outdoor above indoor) (Hermawan)

Oil Separator – separates the oil from the superheated discharge refrigerant vapor and returns it to the compressor crankcase.

1. oil separator image

2. oil separator cutaway image (by Hermawan)

3. Heldon oil separator handbook (PDF)

Oil pressure switch – a differential pressure switch designed to protect the refrigeration compressor if the oil pressure is too low. (Compares crankcase and pump pressure).

1. Emerson oil pressure switches - copeland: technical information guide.

Open circuit – an electrical circuit that is not complete; there is a break in the circuit therefore no current is flowing. An open circuit can be from a switch being open in the circuit or a fault in the circuit.

Ozone (O3) Layer – Ozone is a naturally occurring gas: 10% in the troposphere (10–16 kilometers altitude), and 90% in the stratosphere (50 kilometres altitude). The large amount of ozone in the stratosphere is often referred to as the "ozone layer."

20 Questions about ozone PDF (8MB)

Ozone depletion animation

Ozzy Ozone cartoon

NASA Ozone Layer hole watch website


Parallel – in the same direction. A parallel circuit is where a number of electrical loads are arranged in relation to the one voltage supply to have individual current flow paths.

Pascal (Pa)International System (SI) unit of pressure.

Perpendicularly – straight up and down; vertical or upright.

Pipe Design – the pipe work for refrigeration systems must be sized correctly to ensure sufficient refrigerant flow, and oil return.

Pipe Design – the pipe work for refrigeration systems must be sized correctly to ensure sufficient refrigerant flow, and oil return.

1. Johnson Controls - General Piping Recommendations and Refrigerant Line Length for Split-System Air Conditioners and Heat Pumps

2. McQuay Refrigerant Piping Design Guide

3. Dupont Refrigerant Piping Handbook

Pole – (1) Either terminal of a battery or cell. (2) Either end of a magnet.

Positive Temperature Co-efficient (PTC) – a type of variable resistor used to measure temperature in the HVAC&R industry. As the temperature increases, the probes resistance increases (and vice versa). The correct resistance value for any probe must be read from the manufacturer's data table.

1. PTC Probe application guide - PDF

Potential difference – the work needed to transfer one unit of charge between two points, measured in volts (V).

Potential Relay – a starting device for single phase, cap start cap run (CSCR) motors. At startup The back EMF from the motor operates a relay that drops the start capacitor out of the circuit and leave the compressor operating a permanent split capacitor (PSC) motor.

1. Potential Relay video How a potential relay works

2. Potential Relay video How to wire a potential relay

Potentiometer – a type of variable resistor used for voltage adjustment.

Power – the rate at which energy is converted from one form to another. The unit of measurement of power is the watt (W).

Pressure – (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. (Note: 0 gauge pressure = 100 kPa absolute). Measured with a manometer (see "Manometer").

  • 1. SI unit Pascal (Pa)
  • 2. Derivations from other quantities: p = F / A
  • 3. In SI base units 1 N/m2 or 1 kg/(m·s2)

Pressure Switch – a line voltage (electrical) control that senses system pressure and open and closes at set system pressures. Typically used for low pressure safety and pump down, and high pressure safety and fan control, as well as other applications.

1. Danfoss pressure switch animation.

Pressure Temperature (PT) Chart – a table of data showing the relationship of refigerant boiling (condensation) points at given pressures in the saturated condition. The PT chart can be used to troubleshoot system operation, specifically to check proper low- and high-side pressures, set or measure superheat and subcooling temperatures, and to set pressure controls.

1. Realcold PT Chart (PDF)

2. PT Chart (PDF)


Proton – the positively charged particle of an atom.

Pythagoras Theorem – the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. The theorem can be written as an equation relating the lengths of the sides a, b and c,

a2 + b2 = c2

Psychrometrics (Hygrometry) – the science of studying the thermodynamic properties of moist air and the quantitative interdependence between temperature and humidity.

1. Online psychrometric calculator - (from UIG Inc.)

2. Online psychrometric calculator - (from The Sugar Engineers)

3. Psychrometric overview - (PDF 1 MB)

4. Psychrometrics 101 - (PDF 9 MB)

5. Nautica Psychrometric Chart - (PDF )

6. AIRAH Psychrometric Chart - (PDF)

7. Psychrometric Chart - Sea Level - (JPG)

8. Hermewan Psychrometric Chart - Air conditioning Processes - (JPG)

9. Hermewan Psychrometric Chart - Cooling Process - (JPG)

Pulley – a simple machine that is made with a rope, chain or belt wrapped around a grooved wheel. Pulley systems are used in the air conditiong and refrigeration industries to drive fans and compressors. Also see vee belts Formula: pulley speed a x diameter a = pulley speed b x diameter b. (d1 n1 = d2 n2).

animatd GIF


Q (Volume flow rate)– Represented by the letter Q, volumetric flow rate, (also known as volume flow rate, rate of fluid flow or volume velocity) is the volume of fluid which passes through a given surface per unit time. The SI unit is m3·s−1 (cubic meters per second). It can be calculated using the velocity (in meters per second) of a fluid and multiplying by the area (square meters) of the pipe or duct.


R32 (Difluoromethane) – classified as A2L, or mildly flammable, R32 has a Global Warming Potential (GWP) of 650, which is significantly less than the more commonly used R410A which is 1,980, and Ozone depletion potential of zero.

1. AIRAH Flammable Refrigerant guide (1 MB)


3. Fujitsu R32 Product Training (PDF 3.3 Mb)

Radius (r) – the distance from the centre to the circumference (outside line) of a circle.

Radius and Radians animation (gif image)

Reclaim (refrigerant) – To recover refrigerant from a system into a reclaim cylinder for return to a reclaim facility for reprocessing.

Reclaim & pump down cylinders PDF

Refrigerant Reclaim Australia Reclaimation and destruction of refrigerants website

Reovery & Reclaim

1. Introduction to Recovery

2. Recovery Types

3. Vapour Recovery

4. Liquid Recovery

5. Push-pull Recovery

Refrigerant – The medium used for heat transfer in a refrigerating system, which absorbs heat on evaporating at a low temperature and a low pressure, and rejects heat on condensing at a higher temperature and higher pressure. There are three main classes of Refrigerants:

Primary - used in vapour compression systems: change state twice.(Natural, HFCs and HCFCs - Pure, Azeotropic and Zeoptropic)

Secondary - Do not change state, transfer heat and undergo a sensible (temperature) change only. (water, brine, glycol)

Expendable - change state once and are lost to the environment. (Ice melts at 0 deg C, Dry Ice subliminates at -78 Deg C, liquid nitrogen vapourises at -196 Deg C).

Video - Liquid Nitrogen used to freeze pipes for a valve insertion

2011 Refrigerant Reference Guide (PDF 4Mb)

www.refrigerants.com website

Refrigeration Basics – an introductory refrigeration training course available on CD-ROM or download for PC, Mac or Tablet. Learn about the mechanical refrigeration process and how to diagnose and troubleshoot refrigerant side, air and water and electrical side problems.

Refrigeration Basics Website

Refrigeration cycle (vapour compression cycle) – is one of the many refrigeration cycles widely used to provide air-conditioning refrigeration.

1. Hermewan refrigeration cycle image

2. Refrigeration cycle animation with ph chart.

3. Compressor Refrigeration cycle animation with components.

4. Refrigeration system overview animation with components.

Refrigeration Gauges (Manifold) – The HVAC gauge manifold set consists of a blue low pressure compound (positive and negative pressure)gauge, and a red high pressure gauge. Hose lines enable access to a refrigeration or air conditioning system, and are used to remove or replace refrigerant, pressure test and evacuated HVAC systems.

1. Danfoss Bourdon Tube Animation

2. Refrigeration Gauges Prezi

3. Refrigeration Gauges Animation

Refrigeration oil – The purpose of oil in a refrigeration system is to lubricate the compressor to reduce the friction on metal parts, reducing wear on the compressor and prolongs the life of the system. Refrigerant oil is a special high-temperature formulation designed for use in refrigeration systems, so it is important to use the recommended lubricant for the equipment. Oil that is too heavy will not flow smoothly to all working parts. Oil that is too light will not adhere properly, causing inadequate lubrication.

Rehabilitation – to restore to a condition of good health in order to be able to get back to work.

Relay – switch device operated by electromagnetism.

Relative Humidity (RH%) – is the amount of moisture in the air compared to what the air can "hold" at that temperature and is expressed as a percentage. The RH of air can be found by measuring the 'dry bulb' and 'wet bulb depression' using a sling psychrometer.

1. Sling Psychrometer Type 1 Image

2. Sling Psychrometer Type 2 Image

3. Sling Psychrometer Relative Humidity chart Chart

4. Sling Psychrometer Psychrometric Chart

Residential Air Conditioning – air conditioning systems specifically designed for residential living spaces - house, unit, apartment, townhouse etc. 23 - 25 deg C dry bulb in cooling, and 18 - 21 Deg C DB in heating, humidity 50-60%.

1. Residential ducted air conditioning interactive page

2. CAS Residential air conditioning products brochure PDF

Residual – something that is left over or remaining, eg residual current.

Resistance (R) – the opposition to current flow. In an electrical circuit everything has some resistance, including conductors. The symbol for resistance is R and it is measured in ohms (Ω).

Resistor (R) – A resistor is an electrical component that causes electrical resistance in a circuit. Specified in ohms (Ω), the current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law: V = I x R

1. Resistor colour chart - image

Return Air (RA) – air that is returned to a heating or cooling system from the conditioned space through the return air plenum and ductwork (if fitted).

Reversing valve (RV) – pilot operated 4 way valve used in air conditioning systems that reverses the flow of refrigerant so the unit can cool or heat the conditioned space.

1. Danfoss reversing valve animation

2. Aussie 50 - open reversing valve

Rheostat – a type of variable resistor used to vary current flow.

Rotary Heat Exchanger (also see energy recovery) – a heat recovery wheel is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the heat energy. For example; using toilet or kitchen exhaust air to cool down fresh outside air.

1. Watch the video

2. Animation


Scientific Notation – the way that scientists easily handle very large numbers or very small numbers. For example, instead of writing 0.0000000056, we write 5.6 x 10-9.

Example: 10000 = 1 x 104 and 24327 = 2.4327 x 104

Screws – A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common uses of screws are to hold objects together and to position objects.

1. Allfasteners screw types (PDF 4.5Mb)

2. Allfasteners anchor types (PDF 8.5Mb)

3. Electronix Express All about Screws (PDF500 Kb)

Screw Driver

Sensible heat – When an object is heated, its temperature rises, when heat is removed from an object its temperature falls, the heat added or removed is called sensible heat. Heat that causes a change in temperature in an object is called sensible heat. The formula to calculate the energy required to change sensible heat in a substance of food is Q = m c dt

  • Where:
  • Q = heat supplied (kJ)
  • m = unit mass (kg)
  • c = specific heat ( kJ/kg oK,)
  • dt = temperature change (oK)

Semiconductor – material with electrical conducting properties intermediate between that of metal and insulators.

Series – one after the other. A series circuit is where one load is placed after another in the same circuit , so there is only one path for current flow.

Service Report – Tips on how to write your service report

Shaded Pole Motor – a small squirrel-cage AC motor in which the auxiliary winding is composed of a copper ring or bar surrounding a portion of each pole. This auxiliary single-turn winding is called a shading coil. The direction of rotation is from the unshaded side to the shaded (ring) side of the pole. Low start torque and are only reversible via disassembly and flipping over the stator.

1. Dismantled shaded pole motor image.

Short circuit – a fault condition where a low resistance connection has happened across an electrical circuit resulting in high current flow. Often referred to as a 'short'.

Shunt – a circuit component connected in parallel with another.

SI (Système Internationale) – a metric system of measurements defines seven units of measure as a basic set from which all other SI units are derived. These SI base units and their physical quantities are:

Sight Glass – Sight glasses are used to indicate: 1. The condition of the refrigerant in the liquid line of the plant. 2. The flow in the oil return line from the oil separator.3. The moisture content in the refrigerant.

1. Sight Glass (animated image).

2. Sight Glass 2 (animated image).

3. R22 Sight Glass video.

4. Sight Glass - Dry (Image).

5. Sight Glass - Wet (Image).

Sling Psychrometer – is a simple instrument used to measure wet bulb depression. It consists of two thermometers and the wet-bulb thermometer has an absorbent cover that is soaked in water before using the instrument. A second thermometer, called the dry-bulb thermometer, measures the ambient temperature. Relative humidity and dew point are determined using the difference between the temperatures recorded by the two thermometers - refer to the chart below:

1. Sling Psychrometer Type 1 Image

1. Sling Psychrometer Type 2 Image

1. Sling Psychrometer Relative Humidity chart Chart

1. Sling Psychrometer Psychrometric Chart

Solenoid valve (LLSV) – a direct operated solenoid valve commonly used on pump down systems.

1. Danfoss EVR2 direct operated coil animation

2. Danfoss EVR25 pilot (servo) operated coil animation

3. Solenoid valve - Cutaway image courtesy Hermawan

Specific heat capacity (c) – The Specific Heat is the amount of heat required to change a unit mass (kg) of a substance by one degree ( K) in temperature expressed as kJ/kg oK.

Split Systems – refers to a range of air conditioning units with separate indoor fan coil unit (FCU) and outdoor (condensing) unit with interconnecting pipework and controls.

Heat Pumps page

Star or wye (3 phase winding) – a winding used in a polyphase electric machine in which one terminal of each phase coil is connected to a common point and the other terminals are joined to the outside system.

Static – stationary or not moving. Static electricity relates to a build up of electrical charge without any current flow.

Static Pressure – Static pressure is the measure of the potential energy of a unit of air in the particular cross section of a duct - more simply, the air pressure on the duct wall is considered static and is measured in Pascals (Pa).

Measuring static pressure using a Magnahelic gauge (Image)

Stratosphere – The region of the earth's atmosphere extending from the top of the troposphere (a height of about 10km) to about 50km. The stratosphere is characterized by the presence of relatively high concentrations of ozone.

Image of the layers of the atmosphere.

Sub-cooling (subcooled liquid) – is the temperature fall below the saturated condensing temperature of a liquid medium. It is important for refrigerant leaving the condenser to be sub-cooled by approximately 5 to 10 oC.

Suction Line Accumulator (SLA) – by ensuring only vapour and carry over oil is returns to the compressor, the SLA provides compressor protection by preventing compressor failure due to liquid slugging.

Suction Line accumulator image

Inside a Suction Line accumulator Video

Heldon Suction Line Accumulators PDF

Superheat (suction and discharge) – is the amount of heat added to a vapor to raise the vapor temperature above its boiling (saturation) point corresponding to the pressure at which it is operating. Note: If there is liquid refrigerant present, there can be no superheat.

Superheated Steam Experiment - Video 12MB

Evaporator superheat – Refrigerant enters the evaporator in a partial liquid/vapor mixture. Part of the liquid turns to vapor as it passes through the expansion device by way of pressure drop. The remaining liquid absorbs heat (from the area to be cooled) and turns into (boils or vaporizes) a saturated vapor. Upon leaving the evaporator, the desired refrigerant state in the suction line is a superheated vapor.

Synchronous Speed – of a motor may be determined by the formula SS = 120 * Hz / N

Where Hz=Frequency, and N = Number of Poles

Theoretically, a 117V 60Hz 6-Pole motor has a Synchronous Speed of 120 * 60 / 6 = 1200 RPM In operation, there are losses resulting in SS = 1075 RPM This formula is derived from Hz = (P/2) x (RPM/60) = P * RPM / 2 / 60 = P * RPM / 120 Note that P/2 is the number of PAIRS of poles

Synthetic Greenhouse Gases (SGG) – Refrigerants that are harmful to the environment that may have ozone depletion potential, global warming potential or both. Governemtn controls apply to the import, export and manufacture of a range of environmentally harmful synthetic greenhouse gases including CFC's HCFC's and HFC's.

Australia - Arctick Website


Temperature – is a measure of the average heat or thermal energy of the particles in a substance.

Temperature Glide – the temperature difference that occurs between the vapor state and liquid state during evaporation or condensation at constant pressure, i.e. the temperature in the evaporator and condenser is not constant. Temperature glide occurs in near-azeotropic and zeotropic mixtures.

PT chart and temperature Glide PDF

T.E.W.ITotal Equivalent Warming Impact.  The measure of the global warming impact of equipment based on the total related emissions of greenhouse gases during the operation of the equipment and the disposal of the operating fluids at the end-of-life. Methods of calculating Total Equivalent Warming Impact TEWI) 2012 (4 MB).

Thermal – relates to using, caused by or producing heat.

Thermistor – electrical device that reduces resistance as temperature increases.

Thermocouple – device having junction between two dissimilar metals; when heated an EMF is produced.

Thermocouple video. courtesy Steorn SKDB.

Thermostat – An electrical switch that operates on temperature - setpoint and differential or cut out and cut in. They are often used to control heating and cooling systems as well as fans and other devices.

1. Danfoss Thermostats (PDF)

2. Danfoss Service thermostats (PDF)

Thermodynamics – the study of heat energy (or thermal energy) and the processes by which this energy may be converted into other forms of energy.

Thermopile – several thermocouples joined in series to produce a combined EMF.

Three phase – source of electrical power from three separate alternating voltages that are out of phase with each other by one-third.

Transformer – a device that uses coils to convert AC voltage and current from one value to a different value voltage and current.

1. How transformers work video (18 MB)

2. 240v to 24v transformer image

Transmission load – The transmission load is the heat leakage that infiltrates the refrigerated area through walls, ceilings, roofs, and floors.

Triple Point – the temperature and pressure where solid, liquid and vapor refrigerant can coexist in equilibrium. Animated image showing triple point.

Troubleshoot – trace and correct faults in a mechanical or electronic system. Danfoss troubleshooting guide.

TX ValveThermal eXpansion valve: a refrigerant metering device. (Pbulb = Pspring + Pevaporator).

1. Externally equalised TX valve cutaway image by Hermawan (1MB).

2. Danfoss TX valve animation.

3. Danfoss electronic TX valve animation.

4. Danfoss TX valve - fitters notes.


UEE11 – Refrigeration, Air Conditioning and Appliance Servicing • Qualifications • Skill Sets • Competency Standard Units. EE-Oz UEE11 Brochure.

UEE32211 – This qualification provides competencies to select components, install, set up, test, fault find, repair and maintain refrigeration systems and equipment that apply to food storage and preservation, air conditioning and air distribution equipment in buildings and premises. It includes regulatory requirements for purchasing and handling refrigerants. UE32211 page

Unitary equipment – Air-Conditioner or refrigeration system that is one or more factory-made assemblies containing an evaporator or cooling coil(s), compressor(s), and condenser(s) and may include a heating function. (Package unit).

Ullage space – Cylinders must have a 3% ullage space (vapour space) at 57°C as specified in AS2030. Ullage space is the space provided for vapour volume in a cylinder during the worst summer condition.


Vacuum – an enclosed space entirely devoid of matter, especially air, that has been partially removed so that the matter or gas remaining in the space exerts less pressure than the atmosphere.

Valence shell – the outermost orbit path for electrons in an atom is known as the valence shell or conduction band.

Vapour barrier (Insulation) – A vapor barrier is an impermeable membrane that blocks the flow of air and is essential in preventing the water vapor that is contained in the air entering the insulation. The air within a cold store holds a good deal less water vapour than the air outside. There is a tendency for moisture in the ambient air to pass through the insulation of a cold store to the area of low partial pressure within. When this vapour is cooled, it condenses and at the point where the temperature is 0°C, it freezes to form ice. This process will continue over a long period of time and the build-up of ice will eventually affect the insulation properties of the cold store wall and also weaken the structure of the wall or building.

1. Insulation Panel (image).

Vapour compression system (refrigeration cycle) – is one of the many refrigeration cycles widely used to provide air-conditioning refrigeration. The Vapor Compression Refrigeration Cycle is a process that cools (or heats) an enclosed space to the desired temperature . Heat is transferred to or from the enclosed space and dissipated into the surroundings (using air or water). During the cycle, a substance called the refrigerant circulates continuously through four stages:

1. Compression stage - the pressure of the refrigerant is increased, which raises the temperature above that of the surroundings, and circulated throught the system.

2. Condensation - the natural direction of heat flow allows the release of energy into the surrounding air (or water) and the vapour refrigerant condenses into a liquid.

3. Expansion - the liquid refrigerant pressure is lowered through a metering device (restriction). The refrigerant begins the Evaporation stage and removes heat from the enclosed space (evaporator).

1. Hermewan refrigeration cycle image

2. Refrigeration cycle animation with ph chart.

3. Compressor Refrigeration cycle animation with components.

4. Carnot cycle animation

Variable Refrigerant Flow (VRF) – VRFs come in two system formats, two pipe and three pipe systems. In a heat pump 2 pipe system all of the zones must either be all in cooling or all in heating. Heat Recovery (HR) systems have the ability to simultaneously heat certain zones while cooling others this is usually done through a 3 pipe design, with the exception of Mitsubishi which is able to do this with 2 pipes. In this case the heat extracted from zones requiring cooling is put to use in the zones requiring heating. This is made possible because the heating unit is functioning as a condenser, providing sub-cooled liquid back into the line that is being used for cooling.

1. VRF system schematic

Variable speed drive (VSD) – also known as a variable frequency drive (VFD) - a method of controlling three phase motors by varying the supply frequency (Hz).

1. Yaskawa - How does a VFD work - PDF

Vee Belts – a loop of flexible material used to mechanically link two or more rotating shafts. Belts are looped over pulleys. In a two pulley system, the belt can either drive the pulleys in the same direction, or the belt may be crossed, so that the direction of the shafts is opposite. For example; a motor driving the shaft of a fan coil unit.

Service Manual for vee belts.

Graham Rubber vee belts maintenance.

Ventilation – The process of moving or changing the air into and out of an interior space either naturally or mechanically. Airflow can be forced or induced by using fans, or natural means - using convection and prevailing winds.

Vibration eliminator – a fitting used with reciprocating compressors to reduce the vibration and stress in refrigerant pipework. Installed in the suction or discharge lines near the compressor and must be installed parallel to the compressor crankshaft (see image below).

1. Vibration eliminator cutaway diagram

2. Vibration eliminator installation image

3. Anaconda Vibration Eliminator (PDF)

Volt (V) – derived unit of measure for the potential difference existing between two points on a conductor.

Voltmeter – device used for measuring volts.

Voltage drop – reduction in voltage in a part of a circuit between the power source and the load. Caused by resistance in a DC circuit or impedance in an AC circuit.

Volume flow rate– Represented by the letter Q, volumetric flow rate, (also known as volume flow rate, rate of fluid flow or volume velocity) is the volume of fluid which passes through a given surface per unit time. The SI unit is m3·s−1 (cubic meters per second).


Wall Split – Refers to a wall mounted split system air conditioning unit or heat pump.

1. Split systems page

2. Heat Pumps page

Water Chiller – a system designed to cool a fluid by removing heat from it, either through a vapour – compression or absorption refrigeration cycle. Typically, the fluid used in chillers is water. Once chilled, this water is then used to cool and dehumidify air in a range of air conditioning applications.

Water Chiller Schematic

AIRAH Chiller 101 PDF

Water Valve – A manual or electrical operated valve which provides a flow of water. Used for regulating the flow of water through condensers in refrigeration and air conditioning plant. Danfoss water valve animation

Watt – derived unit of measure for power used when energy is expended at the rate of one joule per second.






Zeotrope – A mixture made up of two or more refrigerants with different boiling points. Zeotropic mixtures are similar to near-azeotropic mixtures with the exception of having a temperature glide greater than 5-7° C. Zeotropic mixtures should be charged in the liquid state..

Zone – A zone in the HVAC industry refers to areas of a building or residence that may have the air flow, space temperature and/or humidity controlled independant of the other zones in the building. For example; a house may have a DAY or Night Zone, a large commercial space may have a PERIMETER (EXTERNAL) and INTERNAL zone, a NORTH zone and a SOUTH zone etc. Zones require equipment and controls capable of regulating airflow, temperature and humidity that vary according to the change in heat load and ambient conditions.