HVAC/R Technical Glossary
A comprehensive definitions index containing essential thermodynamic, mechanical, and technician field terms.
Accumulator
A safety vessel placed on the suction line before the compressor to trap liquid refrigerant and prevent it from entering the crankcase.
Approach Temperature
The difference between the leaving fluid temperature and the saturation temperature of the refrigerant inside the heat exchanger. Lower approach indicates higher heat transfer efficiency.
Azeotrope
A liquid mixture of two or more substances (like R502) that retains its composition and boiling point during distillation, behaving like a single refrigerant.
BTU (British Thermal Unit)
The quantity of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit.
Capillary Tube
A simple metering device consisting of a long copper tube with a tiny inside diameter, restricting refrigerant flow by friction pressure drop.
Centrifugal Compressor
A dynamic compressor that increases pressure by accelerating refrigerant vapor through an impeller and converting kinetic energy to static pressure.
Chiller barrel
A shell-and-tube or plate heat exchanger where chilled water is cooled by evaporating liquid refrigerant.
Coefficient of Performance (COP)
The ratio of heating or cooling capacity produced to the electrical energy consumed. High COP denotes high efficiency.
Compression Ratio
The ratio of absolute discharge pressure (head pressure + atmospheric) to absolute suction pressure (suction pressure + atmospheric).
Condenser
A heat exchanger where high-pressure refrigerant vapor rejects heat to water or air and condenses into a liquid state.
Contactor
An electrical relay switch used to supply high-voltage current to the compressor and condenser fan motors when signaled by the thermostat.
Crankcase Heater
An electrical heating element placed around the compressor base to boil off refrigerant dissolved in the lubrication oil during off-cycles.
Delta T (ΔT)
The difference in temperature between two measured points, such as air entering vs. leaving an evaporator coil.
Dew Point
The temperature at which air becomes saturated with moisture (100% relative humidity) and water vapor begins to condense into liquid droplets.
Dry Bulb Temperature
The ambient air temperature measured by a standard thermometer shielded from radiation and moisture.
Ductwork
A network of metal, plastic, or fiberglass conduits used to distribute conditioned supply air and return air throughout a building.
EER (Energy Efficiency Ratio)
The cooling capacity in BTU/h divided by the electrical power input in Watts at specific rating conditions.
Evaporator
A heat exchanger inside the conditioned space where low-pressure liquid refrigerant absorbs heat and boils into a vapor.
Expansion Valve (TXV)
A control valve that regulates the mass flow of refrigerant into the evaporator based on suction line superheat.
Filter Drier
A dual-purpose refrigeration accessory containing desiccant core materials to absorb moisture and filter debris from the liquid line.
Glide
The temperature difference between the bubble point and dew point of a zeotropic refrigerant blend at a constant pressure.
GWP (Global Warming Potential)
A measure of how much heat a greenhouse gas traps in the atmosphere relative to carbon dioxide (GWP of 1).
Hermetic Compressor
A compressor where the motor and pump are welded inside a single gas-tight steel shell, preventing shaft seal leaks.
HFC (Hydrofluorocarbon)
Refrigerants composed of hydrogen, fluorine, and carbon (such as R134a, R32, R410A) with zero ozone depletion potential.
HCFC (Hydrochlorofluorocarbon)
Refrigerants containing chlorine, fluorine, carbon, and hydrogen (such as R22) being phased out globally due to ozone layer damage.
HFO (Hydrofluoroolefin)
Modern low-GWP refrigerants (like R1234yf) derived from unsaturated organic compounds.
Hygroscopic
The property of absorbing moisture from the surrounding air. Synthetic POE oils are highly hygroscopic.
Latent Heat
Heat energy absorbed or released during a phase change (like boiling or condensing) at constant temperature.
Liquid Line
The copper tube carrying high-pressure liquid refrigerant from the condenser outlet to the metering device.
Manifold Gauge Set
A service tool consisting of high and low pressure gauges, valves, and hoses used to diagnose and charge systems.
Micron
A unit of length equal to one-millionth of a meter. Used to measure vacuum pressure (760,000 microns = atmospheric pressure).
Non-Condensable Gases
Gases like air, nitrogen, or oxygen that do not liquefy in the condenser, raising system pressure and reducing efficiency.
Oil Separator
A mechanical filter on the compressor discharge line that extracts oil and returns it to the crankcase, keeping coils clean.
Psychrometrics
The study of the thermodynamic properties of moist air (humidity, wet bulb, enthalpy, dew point).
R32
A low-GWP, mildly flammable HFC refrigerant used in residential split systems.
R134a
A medium-pressure HFC refrigerant widely used in automotive air conditioning and domestic refrigerators.
R410A
A high-pressure near-azeotropic HFC blend (R32/R125) widely used in residential split air conditioners.
Refrigerant
A thermodynamic fluid that cycle-evaporates at low temperature/pressure and condenses at high temperature/pressure to transfer heat.
Sensible Heat
Heat energy that causes a change in dry bulb temperature of a substance without a change of state.
Short Cycling
A fault condition where the compressor starts and stops in rapid succession, causing electrical and thermal stress.
Slugging
A destructive condition where liquid refrigerant or oil enters the compressor cylinders, causing mechanical valve failure.
Subcooling
The difference between the saturated condensing temperature and the actual temperature of the liquid refrigerant leaving the condenser.
Suction Line
The insulated copper line carrying low-pressure vapor refrigerant from the evaporator outlet to the compressor suction port.
Superheat
The temperature difference between the actual vapor temperature leaving the evaporator and its saturated vapor temperature.
Ton of Refrigeration
A unit of cooling capacity equivalent to the heat extraction rate required to melt 1 short ton (2000 lbs) of ice in 24 hours (12,000 BTU/h).
Vacuum Pump
A mechanical pump used to evacuate air and moisture from a refrigeration circuit before charging.
Wet Bulb Temperature
The temperature measured by a thermometer bulb covered with a water-saturated wick under airflow, indicating evaporative cooling capacity.
Zeotrope
A refrigerant blend (like R407C) composed of multiple components with different boiling points, resulting in temperature glide.