Air sensor - A device that registers changes in air conditions such as pressure, velocity, temperature, or moisture content.

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

Automatic control - Controls that react to a change in conditions to cause the condition to stabilize.

Automatic expansion valve - A refrigerant control valve that maintains a constant pressure in an evaporator.

Bleeding - Allowing pressure to move from one pressure level to another very slowly.

Bore - The inside diameter of a cylinder.

British thermal unit - The amount (quantity) of heat required to raise the temperature of 1lb of water 1'F.

Btu - Abbreviation for British thermal unit.

Burner - A device used to prepare and burn fuel.

Carbon dioxide - A by-product of natural gas combustion that is not harmful.

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

Charge - The quantity of refrigerant in a system. Charging cylinder: A device that allows the technician to accurately charge a refrigeration system with refrigerant.

Chlorofluocarbons (CFC) - Those refrigerants thought to contribute to the depletion of the ozone layer.

Circuit breaker - A device that opens an electric circuit when an overload occurs.

CO2 indicator - An instrument used to detect the quantity of carbon dioxide in flue gas for efficiency purposes.

Code - The local, state, or national rules that govern safe installation and service of systems and equipment for the purpose of safety of the public and trade personnel.

Cold - The word used to describe heat at lower levels of intensity.

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

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

Condensate - The moisture collected on an evaporator coil.

Condensate pump - A small pump used to pump condensate to a higher level.

Condenser - The component in a refrigeration system than transfers heat from the system by condensing refrigerant.

Condensing temperature - The temperature at which a vapor changes to a liquid.

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

Cycle - A complete sequence of events (from start to finish) in a system.

Damper - A component in an air distribution system that restricts air flow from the purpose of air balance.

Dehumidify - To remove moisture from air.

Density - The weight per unit of volume of a substance.

Dew point - The exact temperature at which moisture begins to form.

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 of refrigeration system.

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

Electronic air filter - A filter that changes dust particles using high-voltage direct current and then collects these particles on a plate of an opposite charge.

Energy efficiency ratio (EER) - An equipment efficiency rating that is determined by dividing the output in Btuh by input in watts. This does not take into account the startup and shutdown for each cycle.

Ethane gas - The fossil fuel, natural gas, used for heat.

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

Fahrenheit scale - The temperature scale that places the boiling point of water at 212'F and the freezing point at 32'F.

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

Fan cycling - The used of a pressure control to turn a condenser fan on and off to maintain a correct pressure within the system.

Fan relay coil - A magnetic coil that controls the starting and stopping of a fan.

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

Flue - The duct that carries the products of combustion out of a structure for a fossil-or-solid fuel system.

Fluid - The state of matter of liquids and gases.

Flush - The process of using a fluid to push contaminants from a system. Force - Energy exerted.

Freeze up - Excess ice or frost accumulation on an evaporator to the point that airflow may be affected.

Freon - The trade name for refrigerants manufactured by DuPont.

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.

Gage - An instrument used to detect pressure.

Gas - The vapor state of matter.

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

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

Heat anticipator - A device that anticipates the need for cutting off the heating system prematurely so the fan can cool the furnace.

Heat coil - A device made of tubing or pipe designed to transfer heat to a cooler substance by using fluids.

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 reverse the refrigerant gas flow.

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

Hydrochlorofluorocarbons (HCFC) - Refrigerants thought to contribute to the depletion of the ozone layer although not to the extent of chlorofluorocarbons. ICM motor - Is a variable-speed motor. It adjusts its speed to deliver the right airflow needed by the system.

Ignition transformer - Provides a high-voltage current, usually to produce a spark to ignite a furnace fuel, either gas or oil.

Induced draft motor - The draft developed in the heat exchanger of a gas-fired furnace by a fan located at the outlet of the heat exchanger, May be used with a natural-draft vent, or with a direct vent system: also called fan-assisted or mechanical draft.

Inert gas - A gas that will not support most chemical reactions, particularly oxidation.

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

Junction box - A metal or plastic box within which electrical connections are made.

Limit control - A control used to make a change in a system, usually to stop it when predetermined limits of pressure or temperature are reached.

Line set - A term used for tubing sets furnished by the manufacturer.

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 the expansion device.

Liquid receiver - A container in the refrigeration system where liquid refrigerant is stored.

Melting point - The temperature at which a substance will change from a solid to a liquid.

Modulator - A device that adjusts by small increments of changes.

Molecule - The smallest particle that a substance can be broken into and still retain its chemical identity.

Montreal Protocol - This landmark agreement initially required a production and consumption freeze. The Montreal protocol called for a stepwise reduction and eventual production phase out of various ozone depleting substances in developed countries.

Natural gas - A fossil fuel formed over millions of years from dead vegetation and animals that were deposited or washed deep into the earth.

Neutralizer - A substance used to counteract acids.

Nitrogen - An inert gas often used to "sweep" a refrigeration system to help ensure that all refrigerant and contaminants have been removed.

Oxidation - The combining of a material with oxygen to form a different substance. This results in the deterioration of the original substance.

Ozone - A form of oxygen. A layer of ozone in the stratosphere that protects the earth from certain of the sun's ultraviolet wave lengths.

Package unit - A refrigeration system where all major components are located in one cabinet.

Pilot light - The flame that ignites the main burner on a gas furnace.

Plenum - A sealed chamber at the inlet or outlet of an air handler. The duct attaches to the plenum.

Pressure - Force per unit of area.

Pressure limiter - A device that opens when a certain pressure is reached.

Pressure switch - A switch operated by a change in pressure. Propane - An LP gas used for heat. PSI - Abbreviation for pounds per square inch.

Pump - A device that forces fluids through a system.

Purge - To remove or release fluid from a system.

PVC ( Polyvinyl choride) - Plastic pipe used in pressure applications for water and gas as well as for sewage and certain industrial applications.

R-22 - Monochlorodifluoromethane, a popular refrigerant for air conditioning systems. 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 from a system and store it in an external container without necessary testing of processing it in any way.

Refrigerant recycling - To clean the refrigerant by oil separation and single or multiple passes through devices, such as replaceable core filter-driers, which reduce moisture, acidity and particulate matter. This term usually applies to procedures implemented at the job site or at a local service shop.

Refrigeration - The process of removing heat from a place where it is not wanted and transferring heat to a place where it makes little or no difference. Relay - A small electromagnetic device to control a switch, motor, or valve.

Relief valve - A valve designed to open and release liquids at a certain pressure.

Rollout switch - A heat-sensitive protective device that opens the circuit if flame migrates away from the burner box.

Rotor - The rotating or moving component of a motor, including the shaft.

Scroll compressor - A compressor that uses two scroll-type components to compress vapor.

Seasonal energy efficiency ratio (SEER) - An equipment efficiency rating that takes into account the startup and shutdown for each cycle.

Sensor - A component for detection that changes shape, form, or resistance when a condition changes.

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

Short cycle - The term used to describe the running time (on time) of a unit when it is not running long enough.

Solenoid - A coil of wire designed to carry an electrical current producing a magnetic field.

Split system - A refrigeration or air conditioning system that has the condensing unit remote from the indoor (evaporator) coil.

Steam - The vapor state of water.

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

Temperature - A word used to describe the level of heat of molecular activity.

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

Thermometer - An instrument used to detect differences in the level of heat.

Thermostat - A device that senses temperature change and changes some dimension or condition within to control an 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 evaportator.

Ton of refrigeration - The amount of heat required to melt a ton (2000 lb) of ice at 32'F, 288,000 Btu/24 h, 12,000 Btu/h, or 200 Btu/min.

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

Ultraviolet - Light waves that can only be seen under a special lamp.

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.

Valve - A device used to control fluid flow.

Vapor - The gaseous state of a substance.

Vapor lock - A condition where vapor is trapped in a liquid line and impedes liquid flow.

Vapor pump - Another name for compressor.

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

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

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