Mitsubishi Heavy Industries SRC25QA-S, Technical Manual, Page: 64 / 102

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7 Service Manual for Air Conditioners with Refrigerant Piping Mounted/Using R410A
Refrigerant
(The following is selected from the document published by The Japanese Refrigeration
and Air Conditioning Industry Association)
7.1 Overview
7.1.1 R410A Refrigerant
(1) Using R410A in air conditioners
In 1974, scientists found that the ozone in the upper stratosphere (about 20-40 km away from
the ground) may be damaged by ozone depleting substances such as CFC (chlorofluorocarbon)
and HCFC (hydrochlorofluorocarbon), etc. From then on, many countries have taken various
measures to protect the ozone layer.
As a kind of HCFC, the conventional refrigerant (R22) used in air- conditioners will damage
the ozone layer. Therefore, in accordance with the international protocols (i.e. Protocols of
Montreal (Ozone Depleting Substances)) and the relevant laws and regulations of the various
countries, other refrigerants that will not damage the ozone layer must be used to substitute
R22.
Refrigerants composed of hydrogen (H), fluorine (F) and carbon (C) are called HFC which will
not damage the ozone layer. R410A is a kind of HFC, with a pressure higher than R22 by
about 1.6 times and a performance about the same as R22 at the same temperature of
refrigerant.
(2) Chemical properties of R410A
a) Chemical stability
Like R22, R410A is a harmfulless, inflammable refrigerant with stable chemical properties.
However, just like R22, with a specific gravity of vapor heavier than that of air, if R410A is
leaked to a closed room, it will be distributed at a low level and cause oxygen starvation. If
R410A is directly exposed to fire, it may produce poisonous gas, so be sure to dispose of it in
a place with good ventilation.
b) Compositional variation (property of false azeotropic point)
R410A is a kind of false azeotropic mixture refrigerant composed of R32 and R125. The
“false azeotropic” condition refers to the dew point curve and the boiling point
curve-gas-liquid balanced curve (constant pressure) are located at each other’s peak
respectively. Multi-component refrigerant with this chemical property will not change in
ingredients basically even when its state is changed, such as becoming vapor (or
condensation). Therefore, even in case of gas refrigerant leakage at a position during pipe
mounting, the ingredients of the circulating refrigerant will keep unchanged basically.
Therefore, R410A can basically be disposed of as a single component refrigerant similar to
R22. However, with respect to the charging of R410A, in consideration of the little changes
in ingredients during the conversion from gaseous to liquid state when it is put into the
cylinder, it should be charged in liquid state.
c) Property of pressure
As shown in Table 2, the vapor pressure of R410A is higher than that of R22 by 1.6 times at
the same temperature, so be sure to use the tools and materials designed specifically for
R410A that can bear high pressure for installation and servicing.
Table 1 Comparison of thermo-physical property between
R410A and R22 Table 2 Comparison of pressure of
saturated vapor between R410A and R22
Unit: MPa
R410A R22 Refrigerant R410A R22
Ingredient (wt%) R22/R125
(50/50)
R22
(100)
Temp. (
℃
)
Molecular weight 72.6 86.5 -20 0.30 0.14
Boiling point (
℃
) -51.4 -40.8 0 0.70 0.40
Vapor pressure (25
℃
,
MPa)
1.56 0.94 20 1.35 0.81
Density of saturated
vapor (25
℃
, kg/m
2
)
64.0 44.4 40 2.32 1.43
Inflammability Inflammable Inflammable 60 3.73 2.33
Ozone depletion
potential (ODP) 0 0.055 65 4.15 2.60
Global warming
potential (GWP) 1730 1700 Source: Thermo-physical Properties List,
NIST REFPROP V5.10, etc. prepared by
JRAIA.
Source: Thermo-physical Properties List, NIST REFPROP
V5.10, etc. prepared by JRAIA.