Azeotrope
Refrigerant blends which do not change saturation temperature appreciably as they evaporate (boil) or condense at a constant pressure.

Blends (Mixtures)
Refrigerants consisting of two or more pure compounds.

CFC (Chlorofluorocarbon)
A pure compound consisting of carbon, chlorine and fluorine atoms. These compounds break down into their single components when released into the upper atmosphere. The chlorine atoms then attack and destroy the ozone which is present there to protect the Earth from harmful ultraviolet radiation delivered from the Sun. Ozone depletion is the root concern which lead to the alternative refrigerant movement. (R-12: dichlorodifluoromethane)

Glide
The difference between the starting and ending temperatures of a phase change process by a refrigerant at a constant pressure.

Global Warming Potential (GWP)
A quantitative rating scale which indicates the ability of the refrigerant to act as a greenhouse gas. The reference for the GWP scale is CO2, which has a value of 1.0. It is important to note that GWPs are usually expressed as direct global warming numbers and do not account for indirect global warming due to power generation and consumption.

Halocarbon Global Warming Potential (HGWP)
Similar to the GWP scale, except the reference is R-11, which has a value of 1.0.

HCFC (Hydrochlorofluorocarbon)
A pure compound consisting of carbon, chlorine, fluorine and hydrogen atoms. Due to the presence of the hydrogen atom, these are more stable than their CFC counterparts. This stability curtails the release of the chlorine atom, but does not prevent it entirely. (R-22: chlorodifluoromethane)

HFC (Hydrofluorocarbon)
A pure compound consisting of carbon, fluorine and hydrogen atoms. Due to the lack of a chlorine atom, these pose no threat to the ozone layer upon their release to the atmosphere. (R-134a: 1,1,1,2-tetrafluoroethane)

Hygroscopic
Possessing the marked ability to attract and condense moisture within the material. Due to their high affinity for the water molecule, these substances hold the moisture making it difficult to remove once it is present.

Mineral Oil (MO)
A type of lubricant which has been traditionally used with CFC and HCFC refrigerants. It has a low affinity for moisture.

Near-Azeotrope
A zeotrope blend with a small temperature glide within the application range of the refrigerant. There is no significant effect on system performance, operation or safety.

Ozone Depletion Potential (ODP)
A quantitative rating scale which indicates the ability of the refrigerant to destroy the ozone layer. The scale is referenced to R-12, which has an ODP defined as 1.0. Refrigerants which do not have chlorine (like an HFC) have an ODP of 0.0.

Polyol Ester Oil (POE)
A synthetic lubricant designed for use with the HFC refrigerants. It was necessary to develop this oil so that it would dissolve in the refrigerant and be carried throughout the system and back to the compressor sump. This oil is extremely hygroscopic.

Pure Compound
A single component which does not change its composition (temperature / pressure relationship) when changing phase.

Zeotrope
Refrigerant blends which do change saturation temperature appreciably as they evaporate (boil) or condense at a constant pressure; i.e., they exhibit a large amount of glide.