Whether you are a service technician in the field, a dispatcher for an HVAC company, or a homeowner just wondering what the heck the service technician is talking about, here are a list of definitions that are used daily in the HVAC industry.


Acid – Most commonly created in compressor burnouts, when the refrigerant reaches extremely high temperatures. Acid in a refrigeration system can cause huge problems for compressors.

Air Flow Distribution – The amount of air that is distributed throughout the designated space. Depends mostly on duct work sizing and proper blower motors.

Air Handler – Usually located inside of the home or business, in the attic, garage, or closet. The air handler is one of two main parts to a split air conditioning and heating system, more information can be found here.

Algae – The number one cause of drain line back ups in humid climates. Grows inside of condensation lines especially in areas that have high humidity.

Amps – a.ka. amperage.

Blower Motor – Located inside of the air handler/furnace. Moves the blower wheel to move a volume of air in heating, cooling and ventilation applications.

Blower Wheel – Attached to the blower motor. Blower wheels that get dirty or build up with debris may eventually restrict air flow or rotate out of balance.

Breaker – An over-current protection device. For example, a 30 amp breaker should trip should that line exceed 30 amps.

BTU – British Thermal Unit. The amount of heat needed to change 1 pound of water, by 1 degree, in one hour. When referring to air conditioning, is the amount of BTU’s it can remove in 1 hour. 12,000 BTU’s are equal to 1 ton of cooling.

Burnout – Compressor burnout, occurs when the compressor motor burns out do to open windings, and can heat up so much and actually burn the refrigerant, creating acid.

Capacitor – A device that stores an electric charge and helps give a boost of power to motors and compressors. In the Hvac field there are generally two types of capacitors, run caps and start caps.

Coil – This is where all the heat transfer takes place in the refrigeration cycle. Generally you have an evaporator coil and condensing coil. On a different definition, coils also are part of electrical devices such as transformers.

Compressor – Compresses refrigerant to allow it to flow through the refrigeration cycle. Compressors are found in heat pumps, split systems, mini-splits, wall units, refrigerators and all refrigeration in general. They are basically the heart of the refrigeration cycle and often the most expensive component in an hvac system.

Condensate Drain – Usually made out of pvc, cpvc, or copper, leads the condensate outside of the place or into another main drain of some sort.

Condenser – The outside unit in a central air conditioning and heating split system. Some of the common major components in the condenser are the compressor, coils, and fan motor. Some smaller parts that make up the condenser are capacitors and contactors.

Condensing Coil – Heat exchanger usually located outside in the condenser. It is important that these coils are kept clean and free from debris and surrounding bushes, trees and other obstructions.

Contactor – a relay, that is normally open, and when voltage is applied to the coil it closes completing the circuit. Normally found on outside condensing units supplying power to the compressor and fan motor, and also electric heating systems.

Chiller – commonly found in commercial applications and large buildings, uses chill water to transfer heat from the air handler or fan coil to complete the refrigeration cycle.

Dampers – these can be installed of duct work in zoning systems, so that the designated room can call for heating or cooling.

Dehumidification – the act of removing moisture from the air. In humid climates dehumidification is essential to prevent the growth of bacteria.

Dew Point – this is when the air can no longer hold the moisture in it, and condenses into a liquid. You can find an extremely accurate dew point calculator here.

Drain Pan – Attached to the evaporator coil, collects the condensation, and then drains out through the condensate drain line.

Duct – Insulated material designed to transfer air throughout a place.

Efficiency – The amount of energy an Hvac systems uses to operate, usually calculated by a SEER rating.

Element – in HVAC  the heating element is used in electric heating applications, as air blows over the heated element it absorbs the heat to heat a household or building. Electric heat is one of the least efficient heating methods in HVAC.

Evaporator Coil – One of the most expensive parts in a split air conditioning and heating system. A heat exchanger commonly located in the air handler.

Fan Motor – The motor has blades attached to move a volume of air. In Hvac terminology the fan motor refers to the condensing unit while the blower motor refers to the air handler.

Freon – Trademark name for older types of refrigerant.

Furnace – The place in the HVAC system where the heat transfer takes place when in heating mode, typically in oil or gas systems.

Gas – In Hvac this is usually referred to as refrigerant.

Gauges – A HVAC technicians tool to measure refrigerant pressure, and on some gauges will also measure the temperature in relation to the refrigerant pressure.

Hard Start – aka Start capacitor. Sends extra voltage to help start up compressor. It has been said that start capacitors can help extend the life of a compressor.

Heat Load Calculation – The amount of refrigerant and air flow it is going to take to heat or cool a space or place. Many factors go into heat load calculations.

HEPA – a type of efficient air filter, acronym for High-Efficiency Particulate Air.

High voltage – There is no set voltage to be considered high when it comes to HVAC, but anything over 50 volts is a good place to start. In other applications other than HVAC this has a completely different meaning.

Humidistat – A device that is used to control the humidity level rather than the temperature.

Humidity – Refers to the amount of water vapor in the air. High humidity inside of homes <60% could cause bacterial growth.

HVAC – acronym for heating, ventilation and air conditioning. The additional R stands for refrigeration.

IAQ – Acronym for Indoor Air Quality.

Insulation – A type of material that slows down the heat transfer process. Insulation can be found in duct work, air handlers, suction lines and more.

KW – Kilowatt. 1,000 watts,  1.34 Horse Power, 3.6 megajoules…

Low Voltage – Usually in HVAC any voltage >50 volts.

Microns – The lower the number the deeper the vacuum, as measured with a micron gauge. A good practice for technicians is to pull a vacuum to 500 microns or less.

Mini Split – A ductless split air conditioning or heating system.

Megger (Megaohmmeter) – A Hvac technicians tool that uses high voltage to measure the amount of resistance in an electrical component such as a compressor or fan motor.

Metering Device – a device in the refrigeration cycle that meters the amount of refrigerant the enters the evaporator coil.

MERV – Minimum Efficiency Reporting Value. A rating used for air filters, the higher the MERV rating the more efficient the filter.

Multi-meter – A Hvac technician tool that should be able to measure volts, amps, OHMS, MicroFarads and temperature.

Negative Pressure – an area that has less pressure than the surrounding space. Most new air handlers have the evap coil before the blower motor, meaning the evaporator coil is under negative pressure and the condensate drain line must have a trap to drain properly when the unit is in operation.

Non-Programmable Thermostat – The most simple type of thermostat to operate and set up, cannot be programmed to turn on and off at set days and times.

OHMS – Current is equal to Voltage divided by the resistance.

Package Unit – A single unit that consists of the evaporator, condensing coils, heaters, compressor, fan and blower motor all in one unit. Package units are popular for commercial buildings and mobile homes.

Plenom – Part of the duct work, usually a box, where air is distributed in different directions.

Positive Pressure – In the air handler system, the blower motor is before the coil, and blows air through the coil and out the condensate drain line, thus does not need a trap. E.G. The new Trane Hyperions are positive pressure systems.

Preventative Maintenance (PM) – A series of preventative measures to keep your system operating efficiently. More information can be found here.

Programmable Thermostat – a thermostat that can be programmed to change temperature by day and time.

PURON – a term used by Carrier, Bryant, for the refrigerant 410A.

Radiant Floor Heating – Uses many forms of heat transfer from under the flooring such as convection, conduction and radiation.

Refrigerant – often referred to as FREON, PURON or gas.

Refrigeration – Refers to coolers, chillers. E.G. Wine cooler, Ice Makers, Walk-In Freezers….

Relay – A part that controls the voltage in a sequence, they can be normally open or closed.

Return Air – Air that is being sucked in by the blower to be either dehumidified or heated.

Return Vent – Normally where the air filter goes in some cases. Unlike supply vents return vents are normally not adjustable.

SEER – Seasonal Energy Efficiency Rating. The higher the SEER rating, the more efficient the system is. SEER ratings cannot be measured by technicians in field.

Sequencer – A type of relay usually used for electric heating, where circuits will open in a timed sequence.

Short to Ground – When there is no resistance left from an electrical component to ground. For instance when a compressor is shorted to ground it would be cheaper to buy a new one than to attempt to rebuild it.

Split System – A heating or cooling system that consists of air handler or furnace, and a condenser. Also known as central heating and cooling systems.

Solenoid – a valve that stops of flow of fluid or gas (refrigerant).There are many types of solenoid valves that are used in HVAC applications.

Static Pressure – Measured in inches of water, the pressure inside of the duct work. High static pressure on the supply side could indicate undersized duct work.

Subcool – the difference between the saturation temperature and the actual liquid line temperature. The more heat being transferred the higher the subcooling is. Take the pressure from the liquid line, and find the refrigerant temperature using PT chart, then subtract that from the liquid line temperature, which will need to be taken with a thermocouple clamp to get an accurate reading. Systems that use a TXV metering device should be charged using the subcooling method.

Superheat – the amount of heat absorbed when the refrigerant transfers from liquid to gas in the refrigeration cycle. Systems that have a fixed metering device should be charged by superheat. Superheat can be measured by taking the refrigerant pressure, taking the suction line temperature at the air handler, and subtracting that from the refrigerant temperature.

Supply – The air leaving the air handler or furnace, and us usually directed through supply grills throughout a place.

Thermocouple – a Hvac technicians tool that hooks up to a meter capable of reading temperature. Commonly used to measure the temperature of the liquid, suction and discharge lines.

Ton – A refrigeration ton is also referred to as 12,000 BTU’s. Typical residential homes have air conditioners that are 2-5 tons or more depending on size of home.

Transformer – a device that reduces the amount of voltage. E.G. 240 volts to 24 volts.

TXV – Thermo Expansion Device, Metering Device, TEV, meters the refrigerant from high pressure to low pressure, controlling the amount of refrigerant that goes into the evaporator coil.

Vapor – gaseous state of refrigerant.

Variable Speed – Type of motor that adjusts speed as needed, these types of motors usually have programmed control modules.

Ventilation – changing the amount of air in a place, exhaust fans are one example of a type of ventilation in HVAC.

Windings – Electrical coil found in motors, compressors, contactors, relays, and many other electrical components that are found in Hvac systems.

Zone – Zoning system where dampers are installed in duct work to direct airflow, controlled by a thermostat, in most cases.

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