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Glossary of Terms

“A” Coil – An evaporator coil that can be used for up flow, down flow, and horizontal-flow applications. It actually consists of two coils shaped like a letter “A”.

Accumulator – A storage tank located in the suction line of a compressor. It allows small amounts of liquid refrigerant to boil away before entering the compressor. Sometimes used to store excess refrigerant in heat pump systems during the winter cycle.

Air Conditioner – Equipment that conditions air by cleaning, cooling, heating, humidifying, or dehumidifying it. A term often applied to comfort cooling equipment.

Air Conditioning – A process that maintains comfort conditions in a defined area.

Air Conditioning and Refrigeration Institute (ARI) – A non-profit association that regulates equipment manufacturers and rates that capacity of equipment.

Air Handler – The device that moves the air across the heat exchanger in a forced air system-normally considered to be the fan and its housing.

Air Pressure Control (Switch) – Used to detect air pressure drop across the coil in a heat pump outdoor unit due to ice buildup.

Air Vent – A fitting used to vent air manually or automatically from a system.

Alternative Refrigerant – One of the newer refrigerants that are replacing the traditional CFC refrigerants that have been used for many years. Many of these refrigerants have very low ozone depletion and global warming indices. Some are completely chlorine-free.

Ambient Temperature – The surrounding air temperature around the operating equipment.

Amperage – Amount (quantity) of electron or current flow (the number of electrons passing a point in a given time) in an electrical circuit.

Annual Fuel Utilization Efficiency (AFUE) – The U.S. Federal Trade Commission requires furnace manufactures to provide this rating so consumers may compare furnace performances before purchasing.

Automatic Changeover Thermostat – A thermostat that changes from cool to heat automatically by room temperature.

Auxiliary Drain Pan – A separate drain pan that is placed under an air-conditioner evaporator to catch condensate in the event that the primary drain pan runs over.

British Thermal Unit (BTU) – BTU is the amount (quantity) of heat required to raise the temperature of 1 lb of water 1 degree F.

BTUH – Number of BTU’s in an hour.

Burner – A device used to prepare and burn fuel.

Capacitor – An electrical storage device used to start motors (start capacitor) and to improve the efficiency of motors (run capacitor).

Capacity – The rating system of equipment used to heat or cool substances.

Carbon monoxide – A poisonous, colorless, tasteless gas generated by incomplete combustion.

Check Valve – A device that permits fluid flow in one direction only.

Chlorofluorocarbons (CFCs) – Those refrigerants thought to contribute to the depletion of the ozone layer.

Combustion – A reaction called rapid oxidation or burning produced with the right combination of a fuel, oxygen, and heat.

Compression – A term used to describe a vapor when pressure is applied and the molecules are compacted close together.

Compressor – A vapor pump that pumps vapor (refrigerant or air) from one level to a higher pressure level.

Condensate -The moisture collected on an evaporator coil.

Condenser – The component in refrigeration system that transfers heat from the system by condensing refrigerant.

Condensing Unit – A complete unit that includes the compressor and the condensing coil.

Contactor – A larger version of the relay. It can be repaired or rebuilt and has movable and stationary contacts.

Control system – A network of controls to maintain desired conditions in a system or space.

Cooling Capacity – A measure of the ability of a unit to eliminate heat from a enclosed space.

Corrosion – A chemical action that eats into or wears away material from a substance.

Current Sensing Relay – An inductive relay coil usually located around a wire used to sense current flowing through the wire. Its action usually opens or closes a set of contacts.

Damper – A component in an air distribution system that restricts airflow for the purpose of air balance.

DC Motor – A motor that operates on direct current (DC).

Deep Vacuum – An attained vacuum that is below 250 microns.

Defrost Cycle – The portion of the refrigeration cycle that melts the ice off the evaporator.

Dehumidify – To remove moisture from air.

Dew – Moisture droplets that form on a cool surface.

Dew Point – The exact temperature at which moisture begins to form.

Diffuser – The terminal or end device in an air distribution system that directs air in a specific direction using louvers.

Direct Drive Motor – A motor that is connected directly to the load, such as an oil burner motor or a furnace fan motor.

Distributor – A component installed at the outlet of the expansion valve that distributes the refrigerant to each evaporator circuit.

Drier – A device used in a refrigerant line to remove moisture.

Drip Pan – A pan shaped to collect moisture condensing on an evaporator coil in an air-conditioning or refrigeration system.

Dry Bulb Temperature – The temperature measured using a plain thermometer.

Duct – A sealed channel used to convey air from the system to and from the point of utilization.

ECM Motor – An electronically commutated motor. This DC motor uses electronics to commutate the rotor instead of brushes.

Electric Heat – The process of converting electrical energy, using resistance, into heat.

Electronic Air Filter – A filter that charges dust particles using a high voltage direct current and then collects these particles on a plate of an opposite charge.

Electronic Leak Detector – An instrument used to detect gases in very small portions by using electronic sensors and circuits.

Energy Efficiency Ratio (EER) – EER is an equipment efficiency rating that is determined by dividing the output in Btu/h by the total electrical input in watts under ARI test conditions. This does not take into account the start-up and shutdown for each cycle.

Enthalpy – The amount of heat a substance contains from a predetermined base or point.

Environmental Protection Agency (EPA) – A branch of the federal government dealing with the control of ozone-depleting refrigerants and other chemicals and the overall welfare of the environment.

Evacuation – The removal of any gases not characteristic to a system or vessel.

Evaporation – The condition that occurs when heat is absorbed by liquid and it changes to vapor.

Evaporative Cooling – Devices that provide this type of cooling use fiber mounted in frame with water slowly running down the fiber. Fresh air is drawn in and though the water-soaked fiber and cooled by evaporation to a point close to the wet-bulb temperature of the air.

Evaporator – The component in a refrigeration system that absorbs heat into the system and evaporates the liquid refrigerant.

Evaporator Coil – A network of copper or aluminum tubes filled with refrigerant located inside the home tat take heat and moisture out of indoor air as liquid refrigerant evaporates.

Expansion Metering Device – The component between the high-pressure liquid line and the evaporator that feeds the liquid refrigerant into the evaporator.

Fan – A device that produces a pressure difference in air to move it.

Fan Cycling – The use of a pressure control to turn a condenser fan on and off to maintain a correct pressure within the system.

Filter – A fine mesh or porous material that removes particles from passing fluids.

Filter Drier – A type of refrigerant filter that includes a desiccant material that has an attraction for moisture. The filter drier will remove particles and moisture from refrigerant and oil.

Float Switch – An assembly used to maintain or monitor a liquid level.

Flue Pipe – The pipe that carries products of combustion out of an structure for a fossil fuel or solid fuel system.

Flush – The process of using a fluid to push contaminants from a system. The process is often used when converting an R-22 system to R-410.

Freon – The trade name for refrigerants manufactured by du Pont.

Furnace – Equipment used to convert heating energy, such as fuel oil, gas, or electricity, to usable heat. It usually contains a heat exchanger, a blower, and the controls to operate the system.

Fuse – A safety device used in electrical circuits for the protection of the circuit conductor and components.

Gas – The state of matter.

Gas Valve – A valve used to stop, start, or modulate the flow of natural gas.

Geothermal Heat Pump – A heat pump that uses the earth or water in the earth for its heat sources and sinks.

Global Warming – An earth-warming process caused by the atmospheres absorption of the heat energy radiated form the earth’s surface.

Grille – A louvered component in an air system at the inlet or the outlet of the airflow.

Heat – Energy that causes molecules to be in motion and to raise the temperature of a substance.

Heat Exchanger – A device that transfers heat from one substance to another.

Heat Pump – A refrigeration system used to supply heat or cooling using valves to traverse the refrigerant gas flow.

Heat Transfer – The transfer of heat from a warmer to colder substance.

Heating Capacity – The ability of a unit to add heat to an enclosed space.

HEPA Filter – An abbreviation for high-efficiency particulate arrestor. These filters are used when a high degree of filtration is desired or required.

Hermetic Compressor – A motor and compressor that are totally sealed by being welded in a container.

Horsepower – A unit equal to 33,000 ft-lb of work per minute.

Hot Surface Ignition – A silicon carbide or similar substance is placed in the gas stream of a gas furnace and allowed to get very hot. When the gas impinges on this surface, immediate ignition will occur.

HSPF – Heating seasonal Performance Factor is the total heating output of a heat pump in BTUs during its standard usage period for heating divided by the total electrical energy input in watt-hours during the same period.

Humidifier – A device used to add moisture to the air.

Humidistat – A control operated by change in humidity.

Humidity – Moisture in the air.

HVAC – Heating Ventilation and Air Conditioning abbreviation.

Indoor Air Quality (IAQ) – IAQ is a term that generally refers to the study or research of air quality within homes and the procedures used to improve air quality.

Inefficient Equipment – Equipment that is not operating at its design level of capacity because of some fault in the equipment.

Infiltration – Air that leaks into a structure through cracks, windows, doors, or other openings due to less pressure inside the structure than outside the structure.

Insulation – A substance that is a poor conductor of the flow of heat.

Intermittent Ignition – Ignition system for a gas furnace that operates only when needed or when the furnace is operating.

Kilowatt (kW) –  A unit of electrical power equal to 1,000 watts.

Kilowatt-hour (kWh) – 1 kilowatt (1,000 watts) of energy used for 1 hour.

Latent Heat – Heat energy absorbed or rejected when a substance is changing state and there is no change in temperature.

Leak Detector – Any device used to detect leaks in a pressurized system.

Limit Switch – A switch that is designed to stop a piece of equipment before it does damage to itself or the surroundings, for example, a high limit on a furnace or an amperage limit on a motor.

Line Set – A term used for copper tubing.

Liquid – A substance where molecules push outward and downward and seek a uniform level.

Liquid Line – A term applied in the industry to refer to the tubing or piping from the condenser to expansion device.

Load Matching – Trying to always match the capacity of the refrigeration or air-conditioning system with that of the heat load put on the evaporators.

Metering Device – A valve or small fixed – size tubing or orifice that meters liquid refrigerant into the evaporator.

Micron – A unit of length equal to 1/1,000 of a millimeter, 1/1,000,000 of a meter.

Mold – A fungus found where there is moisture that develops and releases spores.

Off Cycle – A period when a system is not operating.

Ohm – A unit of measurement of electrical resistance.

Organic – Materials formed from living organisms.

Orifice – A small opening through which fluid flows.

Package Unit – A refrigerating system where all major components are located in one cabinet.

Pilot Duty Relay – A small relay that is used in controls circuits for switching purposes. It is small and cannot take a lot of current flow, such as to start a motor.

Pilot Light – The flame that ignites the main burner on a gas furnace.

Potential Relay – A switching device used with hermetic motors that breaks the circuit to the start capacitor and start windings after the motor has reached 75% of its running speed.

Plenum – A sealed chamber at the inlet or outlet of an evaporator coil or air handler. The ducts attach to the plenum.

Pressure Switch – A switch operated by a change in pressure.

Preventive Maintenance – The action of performing regularly scheduled maintenance on a unit, including inspections, cleaning and servicing.  Air Depots Energy Savings Plan – ESP

Programmable Thermostat – An electronic thermostat that can be set up to provide desired conditions at desired times.

Pulse Furnace – This furnace ignites minute quantities of gas 60 times per second. Small amounts of natural gas and ire enter the combustion chamber and are ignited with a spark that forces the combustion materials down a tailpipe to an exhaust coupler.  The pulse is reflected back to the combustion chamber, igniting another gas and air mixture.

Pump Down – To use a compressor to pump the refrigerant charge into the condenser.

Purge – To remove or release fluid from a system.

R-22 – A popular HCFC refrigerant for air conditioning systems.

R-410A (Puron) – Another popular HCFC refrigerant for air conditioning systems which is better for the environment.

Radiant Heat – Heat that passes through air, heating solid objects that in turn heat the surrounding area.

Reciprocating Compressor – A compressor that uses a piston in a cylinder and a back and forth motion to compress vapor.

Recovery Cylinder – A cylinder into which refrigerant is transferred; should be approved by the Department of Transportation as recovery cylinder. The color code for these cylinders is yellow top with gray body.

Refrigerant – The fluid in a refrigeration system that changes from a liquid to a vapor and back to a liquid at practical pressures.

Refrigerant Recovery – To remove refrigerant in any condition form a system and store it in an external container without necessarily testing or processing it in any way.

Register – A terminal device on an air distribution system that directs air but also has a damper to adjust airflow.

Relative Humidity – The amount of moisture contained in the air as compared to the amount the air could hold at that temperature.

Relay – A small electromagnetic device to control a switch, motor or valve.

Scroll Compressor – A compressor that uses two scroll type components, one stationary and one orbiting, to compress vapor.

SEER (Seasonal Energy Efficiency Ration) – An equipment efficiency rating that takes into account the start-up and shutdown for each cycle.

Sensible Heat – Heat that causes a change in temperature.

Sequencer – A control that causes a staging of events, such as a sequencer between stages of electrical heat.

Service Valve – A manually operated valve in a refrigeration system used for various service procedures.

Single Phase – The electrical power supplied to equipment or small motors, normally under 7 ½ horsepower.

Specific Heat – The amount of heat required to raise the temperature of 1 lb of a substance 1 degree F.

Split System – A refrigeration or air conditioning system that has the condensing unit remote form the indoor evaporator coil.

Squirrel Cage Fan (Blower Wheel) – A cylindrically shaped fan assembly used to move air.

Standing Pilot – Pilot flame that remains burning continuously.

Start Capacitor – A capacitor used to help an electric motor start.

Starting Relay – An electrical relay used to disconnect the start capacitor and start winding in hermetic compressor.

Stress Crack – A crack in piping or heat exchanger caused by age or abnormal conditions such as vibration.

Subbase – The part of a space temperature thermostat that is mounted on the wall and to which the interconnecting wiring is attached.

Subcooling – The temperature of a liquid when it is cooled below its condensing temperature.

Suction Line – The pipe that carries heat-laden refrigerant gas from the evaporator coil to compressor.

Superheat – The temperature of vapor refrigerant above its saturation change-of-state temperature.

Sweating – A word used to describe moisture collection on a copper line or evaporator coil that is operating below the dew point temperature of the air.

Technician – A person who performs maintenance, service, testing, or repair to air conditioning equipment.

Temperature – A word used to describe the level of heat or molecular activity, expressed in Fahrenheit or Celsius.

Therm – Quantity of heat, 100,000 Btu.

Thermocouple – A device made of two unlike metals that generates electricity when there is a difference in temperature form one end to the other. Thermocouples have a hot and cold junction.

Thermostat – A device that senses temperature change and changes some dimension or condition within to control and operating device.

Thermostatic Expansion Valve (TXV) – A valve used in refrigeration systems to control the superheat in an evaporator by metering the correct refrigerant flow to the evaporator coil.

Three Phase – A type of power supply usually used for heavy loads. It consists of three sine waves that are out of phase by 120 with each other.

Time Delay – A device that prevents a component from starting for a prescribed time. For example, many systems start the fans and use a time delay relay to start the compressor at a later time to prevent too much inrush current.

Ton of Refrigeration (TON) – The amount of heat required to melt a ton (2,000 lb) of ice at 32 F in 24 hours, 288,000 Btu/24 h, 12,000 Btu/h, or 200 Btu/min.

Total Heat – The total amount of sensible heat and latent heat contained in a substance from a reference point.

Transformer – A coil of wire wrapped around an iron core that induces a current to another coil of wire wrapped around the same iron core.

Two Speed Compressor Motor – Can be a four-pole motor that can be connected as a two-pole motor for high speed (3,450 rpm) and connected as a four-pole motor for running at 1,725 rpm for low speed. This is accomplished with relays outside the compressor.

Ultraviolet Lamp  – Light  frequency between 200 and 400 nanometers.

Upflow Furnace – This furnace takes in air form the bottom  or from sides near the bottom and discharges hot air out the top.

Vacuum – The pressure range between the earth’s atmospheric pressure and no pressure, normally expressed in inches of mercury vacuum.

Vacuum Pump – A pump used to remove some fluids such as air and moisture from a system at a pressure below the earth’s atmosphere.

Vapor – The gaseous state of a substance.

Vaporization – The changing of a liquid to a gas or vapor.

Variable Speed Motor – A motor that can be controlled, within an electronic system, to operate at more than one speed.

V Belt – A belt that has a v-shaped contact surface and is used to drive compressors, fans or pumps.

Velocity – The speed at which a substance passes a point.

Ventilation – The Process of supplying and removing air by natural or mechanical means to and from a particular space.

Voltage – The potential electrical difference for electron flow form one line to another in an electrical circuit.

Watt – A unit of power applied to electron flow. One watt equals 3.414 Btu.

Window Unit – An air conditioner installed in a window that rejects the heat outside the structure