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Modern Refrigeration and Air Conditioning
the previous categories. Refrigerants in this category
include butane and pentane. Inorganic refrigerants are
refrigerants that typically do not contain carbon, such
as hydrogen, oxygen, water, and ammonia. Unsaturated
organic compounds are used in the manufacture of
plastics such as vinyl chloride.
Pro Tip
Carbon Dioxide
Carbon dioxide (CO2) is a simple oxide of carbon
and is not classifi ed as an organic compound. For this
reason, it is categorized as an inorganic refrigerant..rigerantfre
6.3.2 Refrigerant Numbering System
The refrigerant numbering system includes three
numbers in a refrigerant designation. The numbers are
identified from right to left. The third number from the
right indicates the series or classification of the refrig-
erant, refer to Figure 6-4.
For refrigerants included in the 000, 100, 200, and
300 series, the third number from the right denotes the
series of the refrigerant and also the number of carbon
atoms in one molecule of the refrigerant minus one.
The second number from the right equals the number
of hydrogen atoms in the refrigerant plus one. The first
number on the right represents how many fluorine
atoms are in the refrigerant.
R-134a is an HFC refrigerant. The chemical name
for R-134a is 1,1,1,2-tetrafluoroethane, and its chemical
formula is CH
2
FCF
3
. The third number from the right
in R-134a is one; therefore, it is classified as an ethane-
based refrigerant. R-134a has two carbon atoms since the
third number from the right also represents the num-
ber of carbon atoms minus one. The second number
C arbon Dioxide
Carbon dioxide ( CO
2
) is a simple oxide of carbon
and is not classi fi ed as an organic compound. For this
reason, it is categorized as an inorganic
from the right is the number of hydrogen atoms in the
refrigerant plus one. Therefore, R-134a has two hydro-
gen atoms. The first number on the right is the num-
ber of fluorine atoms. R-134a has four fluorine atoms.
Figure 6-5 illustrates the common numbering system
approved by ASHRAE. Refrigerants with lowercase
letters at the end of the title are used to differentiate
between isomers. Isomers are molecules that have an
identical number of atoms, but the atoms are arranged
differently in different isomers. As a result, isomers can
have the same number of atoms but different properties
and characteristics.
Some fluorocarbon refrigerant numbers have only
two digits, such as R-22 (CHClF
2
). Since the refrigerant
has only one carbon atom, the third number from the
right is zero. When the third digit is zero, it is dropped.
The second number from the right is two because the
refrigerant has one hydrogen atom. Because the refrig-
erant has two fluorine atoms, the first number from the
right is also two.
For refrigerants in series 400, 500, 600, and 1000,
the third number from the right identifies the series of
the refrigerant, and the two numbers that follow it are
assigned sequentially. These numbers do not denote
the specific chemical structure. The numbers assigned
to zeotropic and azeotropic blends may be followed by
an uppercase letter. These letters denote blends that
have the same component refrigerants, but at different
ratios. For example, R-421A and R-421B are both com-
posed of R-125 and R-134a. However, R-421A is made
up of 58% R-125 and 42% R-134a, while R-421B is made
up of 85% R-125 and 15% R-134a.
For series 700 refrigerants, the third number from
the right denotes the series. The next two numbers
indicate the molecular weight of the refrigerant. For
example, R-717 is composed of one nitrogen atom
(molecular weight of 14) and three hydrogen atoms
(molecular weight of 3).
Instead of the prefix R, refrigerants can also be
labeled with the prefix CFC, HCFC, or HFC, depend-
ing on which type of refrigerant they are. Thus, R-12 is
the same as CFC-12.
Goodheart-Willcox Publisher
Figure 6-4. Refrigerants are categorized in the ASHRAE
numbering system according to their molecular structure.
Chemical Classifi cations of Refrigerants
Series Refrigerant Classifi cation
000 Methane based
100 Ethane based
200 Propane based
300 Cyclic organic
400 Refrigerant blends—zeotropes
500 Refrigerants blends—azeotropes
600 Miscellaneous organic
700 Inorganic
1000 Unsaturated organic
1,1,1,2-tetrafluoroethane (CH2FCF3)
R-134a
Refrigerant
Carbon atoms –1
Hydrogen atoms +1
Fluorine atoms
Indicates unbalanced isomer
Goodheart-Willcox Publisher
Figure 6-5. By understanding the numbering system, you can
determine the chemical components of each refrigerant.