AC Abbreviation for alternating current, a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse.
AC or DC Abbreviation for equipment capable of operating on alternating or direct current.
A-Coil A heat exchanger consisting of two diagonal coils that are joined together in a manner that looks like the letter "A".
Air Conditioner Any device that can change the temperature, humidity or general quality of the air.
Air cleaner Any device that removes undesirable particles from moving air.
Air flow volume The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.
Air handler An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed.
BTU British thermal unit; the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.
BTUh British thermal units per hour. 3412 BTUh equals one kilowatt-hour.
Capacity The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.
Celsius The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C". To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).
CFM Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm per ton of air conditioning.
Charge To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.
Compressor This is the heart of a heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.
Condensate Vapor that liquefies due to the lowering of its temperature to the saturation point.
Condenser coil (or outdoor coil) In a heat pump, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In a heat pump system, the coil absorbs heat from the outdoors.
Condenser fan The fan that circulates air over the air-cooled condenser.
Contactor A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.
COP Coefficient of performance
Crankcase heaterThis is the electric resistance heater installed on compressor crankcases to boil off liquid refrigerant that may have combined with compressor oil. Many newer cooling systems do not require crankcase heaters, however heat pumps do require crankcase heaters.
DC Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.
Defrost To melt frost; as in from an air conditioner or heat pump coil.
Dehumidifier An air cooler that removes moisture from the air.
Downflow furnace A furnace that intakes air at its top and discharges air at its bottom.
Drain pan This also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).
Dry bulb temperature Heat intensity, measured by a dry bulb thermometer.
Dry bulb thermometer An instrument that measures air temperature independently of humidity.
DX Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.
EER Energy Efficiency Ratio (steady state)
Expansion Valve A refrigerant-metering valve with a pressure or temperature controlled orifice.
Fahrenheit The temperature scale on which water freezes at 32 degrees and boils at 212 degrees; designated by the letter F. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5 and divide by 9 (77 -32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius).
Fan Any device that creates air currents.
Filter Any device that removes impurities through a straining process.
Fuse A metal strip in an electrical circuit that melts and breaks the circuit when excessive current flows through it. The fuse is designed to break in order to save more expensive electrical components.
Heat Exchanger An area, box or coil where heat flows from the warmer to the colder fluid or surface.
Heat Gain Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.
Heating Coil Any coil that serves as a heat source.
Heat Loss The rate of heat transfer from a heated space to the outdoors.
Heat Pump A mechanical-compression cycle refrigeration system that can be reversed to either heat or cool the controlled space.
Heat Transfer The movement of heat energy from one point to another. The means for such movement are conduction, convection, and radiation.
Hertz In alternating current (AC electricity), the number of cycles per second.
HSPF Heating Seasonal Performance Factor. This rating is used in measuring the heating efficiency of a heat pump. The higher the number the more efficient the heat pump system.
Humidifier A machine that adds water vapor to the air to increase humidity.
Humidity The presence of water vapor in the air.
Humidity, absolute Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.
Humidity, relative The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.
Ignition The lighting of a fuel to make it burn.
Kilowatt (kW) 1,000 watts.
Latent Heat A type of heat, which when added to or taken from a substance, does not change the temperature of the substance. Instead, the heat energy enables the substance to change its state.
Media The material in a filter that traps and holds the impurities.
OEM Original equipment manufacturer.
Orifice An opening or hole; an inlet or outlet.
Package Unit A heating and cooling system contained in one outdoor unit. A package unit is typically installed beside, on the roof, or sometimes in the attic of a home.
PSI Pounds per square inch.
PSIA Pounds per square inch, absolute.
PSIG Pounds per square inch gauge.
PVC Polyvinyl chloride; a type of plastic.
Reciprocating CompressorA compressor whose piston or pistons move back and forth in the cylinders.
Refrigerant A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-22 refrigerant. R-22 is regulated under the Montreal Protocol. R-22 is scheduled to be in production until the year 2020. It's used in approximately 95 percent of heat pumps manufactured today.
Refrigerant Charge The required amount of refrigerant in a system.
SEER Seasonal Energy Efficiency Ratio; a measure of cooling efficiency for air conditioners and heat pumps. The higher the SEER, the more energy efficient the unit.
Self-contained System A refrigerating system that can be moved without disconnecting any refrigerant lines; also know as a package unit.
Sensible Heat That heat which, when added to or taken away from a substance, causes a rise or fall in temperature.
Sensor Any device that reacts to a change in the conditions being measured, permitting the condition to be controlled.
Set point The temperature or pressure at which a controller is set with the expectation that this will be a nominal value depending on the range of the controller.
SF Side fan series
Split System The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.
TF Top fan series
Thermostatic Expansion Valve A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat; also called a thermal expansion valve.
Thermostat A thermostat consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.
Ton A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.
Two-stage heating / Two-stage cooling Two-stage heating and cooling is considered to be more efficient, because it operates at low speed most of the time. However, on days when more heating or air conditioning is required, it switches to the next stage for maximum comfort.
U-Factor The factor representing resistance to heat flow of various building materials.
Up flow Furnace A furnace in which air is drawn in through the sides or bottom and discharged out the top.
Vacuum A pressure below atmospheric pressure. A perfect vacuum is 30 inches Mercury (periodic symbol "Hg").
Variable-speed motor(s) The fan motor is designed to vary its speed based on your home's heating and air conditioning requirements. Working in conjunction with your thermostat, it keeps the appropriate-temperature air (e.g. warm air on cold days) circulating throughout your home, reducing temperature variances in your home. It also provides greater air circulation and filtration, better temperature distribution, humidity control, higher efficiency, and quiet performance.
Volt The unit of measure used to describe a difference in electrical potential; abbreviated by the symbol "v".
Voltage The force that pushes electrical current along wires and cables.
Watt The unit of electrical power equal to the flow of one amp at a potential difference of one volt.
Wet Bulb Thermometer A thermometer whose bulb is covered with a piece of water-soaked cloth. The lowering of temperature that results from the evaporation of water around the bulb indicates the air's relative humidity.