Refrigerating system and operating method thereof

A refrigerating system having a refrigerating cycle constructed by connecting an accumulator, a refrigerant compressor, a four-way valve, an outdoor unit heat exchanger, an outdoor unit expander, a receiver, an indoor unit expander and an indoor unit heat exchanger sequentially by pipes. Normally, excessive refrigerant is stored in the receiver and when it becomes necessary to raise a ratio of lower boiling point refrigerants, a flow amount of the refrigerant is decreased by restricting the outdoor unit expander during the cooling operation or by restricting the indoor unit expander during the heating operation to move the excessive refrigerant within the receiver to the accumulator. Thereby, the composition of the refrigerant circulating within the refrigerating system using non-azeotrophic refrigerant mixtures may be changed without using a complicated system structure or control method thereof and the capacity of the refrigerating cycle may be changed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an air conditioner, comprising a 
refrigerating system having a receiver and an accumulator for storing 
excessive refrigerant, which operates so as to increase a lower boiling 
point refrigerant and which is suited for enhancing a capacity variable 
function of the air conditioner at low cost and for stabilizing the 
refrigerating cycle thereof. 
2. Description of the Related Art 
A capacity variable function is necessary to improve the comfortableness or 
to save energy of an air conditioner and the needs thereof is increasing 
year by year. As means for varying the capacity, capacitance control of a 
compressor whose number of revolutions can be varied by using an inverter 
is often used. This method, however, has had a problem that it 
significantly adds to the cost of the equipment. 
There has been also known a method of changing the composition of 
refrigerant circulating within a refrigerating cycle during the operation 
thereof by using non-azeotrophic refrigerant mixtures, though the capacity 
variable range thereof is narrower than that of the method utilizing the 
inverter. 
As described in Japanese Patent Laid-Open No. 62-52368 and Patent Laid-Open 
No. Hei. 1-88068 for example, the method of using the non-azeotrophic 
refrigerant mixtures in which more than two kinds of substances having 
different boiling points are compounded changes the composition of the 
circulating refrigerant by distilling it by providing a refrigerant 
rectifier unit or a refrigerant separator, together with heat exchanger 
means. 
A method described in Japanese Patent Laid-Open No. 61-55562 controls the 
cooling and heating capability by storing liquid refrigerant in a 
gas-liquid separator. 
The methods described above, however, require a special mechanism for 
controlling the composition, besides those structural elements which the 
normal refrigerating cycle is equipped with. Due to that, they have had 
problems that the system structure and the system control are complicated, 
that the system is costly and that the reliability thereof drops due to 
the instability of the control. 
Meanwhile, a method of charging an amount of refrigerant sufficient for the 
longest pipe in advance is adopted for air conditioners to reduce labor in 
installation works. When an operating capacity fluctuates in such air 
conditioner or a multiple air conditioner in which a plurality of indoor 
units are connected to one outdoor unit, excessive refrigerant is produced 
in the air conditioner. Then, in order to absorb the excessive 
refrigerant, a receiver is provided at the outlet of a condenser as a 
refrigerant storage tank or an accumulator is provided before a 
refrigerant compressor. Then, if the composition of the non-azeotrophic 
refrigerant can be changed by using those structural elements, the air 
conditioner can be constructed without providing other special elements. 
Further, HCFC 22, a refrigerant which had been widely used for 
refrigeration and air-conditioning, has been decided to be totally 
eliminated in the future because it is involved in the destruction of the 
ozonosphere, and the regulation on its usage is been tightened year by 
year. Due to that, a substitute for HCFC 22 has been demanded and as a 
candidate thereof, non-azeotrophic refrigerant mixtures of HFCs which are 
non-chloric fluorocarbon and which will not destroy the ozonosphere is 
hopeful. 
In concrete, a substance in which HFC 32, HFC 125 and HFC 134a are mixed in 
the ratio of 23:25:52 (weight %) has been given a refrigerant No. R407C by 
ASHRAE and is about to be put into practical use. Further, a binary 
refrigerant mixture of HFC 32 and HFC 134a, which is superior in terms of 
the efficiency, the problem of global warming and the production cost, may 
be used, provided that its problem of flammability is solved. 
Because HCFC 22 is replaced with such new non-azeotrophic refrigerant 
mixtures from now on, it is required to establish the technology for 
varying the composition of the circulating refrigerant. 
It is also required to reduce an amount of charged refrigerant in order to 
reduce the influence on the global warming and to reduce the cost of the 
units. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to solve the 
aforementioned problems of the prior art by providing a refrigerating 
system which can readily change the composition of circulating refrigerant 
in the system using non-azeotrophic refrigerant mixtures, i.e. a 
refrigerant in which more than two kinds of substances having different 
boiling points are mixed, by using only the structural elements used in 
the conventional refrigeration cycle. 
It is another object of the present invention to provide the refrigerating 
system, using the non-azeotrophic refrigerant mixtures, in which an amount 
of refrigerant used is reduced. 
It is a further object of the present invention to provide a method for 
operating the refrigerating system which can change the composition of the 
refrigerant circulating within the refrigerating system effectively while 
keeping the stable condition, while maintaining a wide operational range 
of the refrigerating system. 
In order to achieve the aforementioned goals, the refrigerating system of 
the present invention in which an indoor unit and an outdoor unit are 
connected through pipes and in which the non-azeotrophic refrigerant 
mixtures is used comprises an outdoor unit expander whose restriction may 
be changed; an indoor unit expander whose restriction may be changed 
similarly; a receiver provided between the outdoor unit expander and the 
indoor unit expander; and a controller for turning both of a refrigerant 
flow at the inlet of the receiver and a refrigerant flow at the outlet 
thereof into a gas-liquid two-phase flow by changing the restriction of 
the outdoor unit expander and the indoor unit expander. 
Further, a refrigerating system having a refrigerating cycle constructed by 
connecting a refrigerant compressor, condenser, a receiver, an evaporator 
and an accumulator sequentially by pipes and whose refrigerant circulating 
within the refrigerating cycle is non-azeotrophic refrigerant mixtures in 
which more than at least two kinds of substances having different boiling 
points are mixed, comprises first expanding means which is provided on the 
upstream side of the receiver and whose restriction may be changed; second 
expanding means which is provided on the downstream side of the receiver 
and whose restriction may be changed; and control means for turning both 
of a refrigerant flow at the inlet of the receiver and a refrigerant flow 
at the outlet thereof into a gas-liquid two-phase flow by changing the 
restriction of the first expanding means and the second expanding means. 
It further comprises control means for reducing liquid refrigerant within 
the receiver and increasing liquid refrigerant within the accumulator by 
changing the restriction of the first expanding means and the second 
expanding means. 
It further comprises a pipe, provided in the receiver, for taking out the 
liquid refrigerant; and gas refrigerant mixing means provided on the pipe 
for taking out liquid refrigerant. 
In the refrigerating system described above, the non-azeotrophic 
refrigerant mixtures is what at least either difluoromethane or 
pentafluoroethane is mixed with 1,1,1,2-tetrafluoroethane. 
The refrigerating system described above further comprises outside air 
temperature detecting means for detecting an outside air temperature and 
the restriction of the first expanding means and the second expanding 
means is controlled based on the outside air temperature. 
The refrigerating system further comprises indoor unit temperature 
detecting means, provided in the indoor unit, for detecting a suction 
temperature of the indoor unit and the restriction of the outdoor unit 
expander and the indoor unit expander is controlled based on the suction 
temperature of the indoor unit. 
In the refrigerating system described above, the refrigerant compressor is 
equipped with discharge pressure detecting means for detecting a discharge 
pressure and the restriction of the first expanding means and the second 
expanding means is controlled based on the discharge pressure. 
In the refrigerating system described above, the refrigerant compressor is 
equipped with discharge temperature detecting means for detecting a 
discharge temperature and the restriction of the first expanding means and 
the second expanding means is controlled based on the discharge 
temperature. 
The refrigerating system further comprises indoor unit blowoff temperature 
detecting means, provided in the indoor unit, for detecting a blowoff 
temperature of the indoor unit and the restriction of the outdoor unit 
expander and the indoor unit expander is controlled based on the blowoff 
temperature of the indoor unit. 
In the refrigerating system described above, the non-azeotrophic 
refrigerant mixtures is R407C. 
Further, a method for operating a refrigerating system equipped with an 
indoor unit and an outdoor unit comprising a refrigerant compressor, an 
outdoor unit heat exchanger, a receiver and an accumulator and using 
non-azeotrophic refrigerant mixtures is characterized in that an amount of 
the zeotropic refrigerant mixtures stored in the accumulator is increased 
during the heating operation when an outside air temperature drops. 
The method described above is also characterized in that an amount of the 
non-azeotrophic refrigerant mixtures stored in the receiver provided 
between an outdoor unit expander and an indoor unit expander is decreased 
during the heating operation when an outside air temperature drops. 
The method described above is also characterized in that the 
non-azeotrophic refrigerant mixture store in the accumulator is increased 
during the defrosting operation. 
The method described above is also characterized in that the restriction of 
the outdoor unit expander and the indoor unit expander is controlled to 
increase lower boiling point refrigerants of the non-azeotrophic 
refrigerant mixtures circulating within the refrigerating cycle during the 
heating operation when an outside air temperature drops. 
In the method described above, the restriction of the outdoor unit expander 
and the indoor unit expander is controlled based on at least either the 
outside air temperature or the suction temperature of the indoor unit. 
When the refrigerating system in which the receiver is installed at the 
outlet of the condenser is operated, the excessive refrigerant within the 
refrigerating cycle is stored in the receiver in the state of saturated 
liquid (liquid refrigerant). At this time, the refrigerant contains a few 
bubbles at the inlet of the receiver and its dryness is almost zero. The 
gas refrigerant of such bubbles is then condensed by the heat radiating 
effect of the receiver and the dryness of the refrigerant at the outlet of 
the receiver becomes zero. 
Thus, the balance of the gas refrigerant and the liquid refrigerant is 
taken at the outlet and inlet of the receiver, keeping the liquid level 
constant. As a result, the refrigerating cycle is stabilized. 
The composition of the non-azeotrophic refrigerant mixtures such as R407C 
in the liquid phase and gas phase changes depending on the dryness in the 
saturation domain. In the liquid phase, its composition turns into what at 
the time when the dryness is zero, i.e. a composition in which a higher 
boiling point refrigerant is contained more than that at the time when the 
refrigerant has been charged. Accordingly, when the dryness of the 
refrigerant stored in the receiver is zero or close to zero, the 
fluctuation of circulation caused by the fluctuation of the composition of 
the stored refrigerant is negligible. 
Meanwhile, the capacity of the refrigerating system is determined by a 
rated standard condition. However, the refrigerating system in which the 
refrigerant compressor is operated at a constant rate cannot exhibit its 
full capacity when the heating operation is performed when an outside air 
temperature is low. Then, in order to bring out the capacity of the 
refrigerating system, the composition of the refrigerant must be changed 
during the operation. 
That is, when the restriction of the first expanding means provided on the 
upstream side of the receiver is restricted, the refrigerant is put into 
the saturation domain at the inlet of the receiver and the flow of the 
refrigerant is turned into a gas-liquid two-phase flow. Thereby, the 
balance of the gas-liquid flow amount of the refrigerant flowing in or 
flowing out of the receiver is lost and the gas refrigerant flowing into 
the receiver pushes down the liquid level, releasing the excessive 
refrigerant stored in the receiver to the refrigerating cycle. The 
released excessive refrigerant circulates through the second expanding 
means and the evaporator provided on the downstream side of the receiver. 
Meanwhile, the restriction of the second expanding means is controlled in 
accordance to the operation of the first expanding means so that the 
refrigerant at the outlet of the evaporator becomes wet, without being 
completely gasified. The refrigerant which has been put into the wet state 
at the outlet of the evaporator flows into the accumulator in the 
gas-liquid two-phase state having a large dryness. A lower boiling point 
refrigerant having a higher capacity increases in the gas refrigerant 
within the two-phase refrigerant having the large dryness, while a higher 
boiling point refrigerant increases in the liquid refrigerant within the 
two-phase refrigerant. 
Items of the outlet of the accumulator such as the size and withstanding 
pressure are designed so that the excessive liquid refrigerant flowing 
therein can be stored, so that the liquid refrigerant containing a large 
amount of the higher boiling point refrigerant may be stored. Then, 
because the liquid refrigerant in which the higher boiling point 
refrigerant has increased is held in the accumulator, the lower boiling 
point refrigerant increases in the refrigerant circulating within the 
refrigerating cycle in contrary. 
The change described above allows the refrigerating cycle to be operated 
with the composition of the refrigerant having higher pressure and higher 
capacity and the capacity of the air conditioner or the refrigerating 
system to be enhanced as a result. 
Further, gas refrigerant mixing means is provided on the pipe, provided in 
the receiver, for taking out liquid refrigerant to turn the refrigerant at 
the inlet and outlet of the receiver into the gas-liquid two-phase state, 
so that the flow within the liquid pipe connecting the indoor unit and the 
outdoor unit can be always the gas-liquid two-phase flow even if the 
refrigerant flows in the both directions and the receiver is provided only 
in the outdoor unit side like a heat pump type air conditioner. As a 
result, an amount of the refrigerant within the pipe can be decreased and 
an amount of refrigerant charged be decreased. 
Still more, the composition of the refrigerant is changed when a 
predetermined condition is met based on information on an outside air 
temperature, a suction temperature of the indoor unit, a discharge 
pressure, a discharge temperature or a blowoff temperature of the indoor 
unit, so that the limit of the operable range which is otherwise caused by 
an increase of an operating pressure when the refrigerating system is 
operated by increasing the lower boiling point refrigerant may be reduced 
and the function for varying the composition of the refrigerant may be 
effectively used.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will be explained with 
reference to FIGS. 1 or 2. 
FIG. 1 shows an air conditioner as a refrigerating system. The air 
conditioner is constructed by connecting a refrigerant compressor 1, a 
four-way valve 3, an outdoor unit heat exchanger 4, an outdoor unit 
expander 6, a receiver 7, an indoor unit expander 8, an indoor unit heat 
exchanger 9 and an accumulator 2 sequentially by pipes. 
An indoor unit fan 10 is disposed near the indoor unit heat exchanger 9. 
The indoor unit heat exchanger 9 and the indoor unit fan 10 constitute the 
main part of an indoor unit 12. An outdoor fan 5 is disposed near the 
outdoor unit heat exchanger 4. 
An outdoor unit 11 of the air conditioner comprises the refrigerant 
compressor 1, the four-way valve 3, the outdoor unit heat exchanger 4, the 
outdoor unit expander 6, the receiver 7 and the accumulator 2. Among the 
pipes described above, the one connecting between the indoor unit heat 
exchanger 9 and the four-way valve 3 is a gas refrigerant connecting pipe 
13 and the other one connecting between the receiver 7 and the indoor unit 
expander 8 is a liquid refrigerant connecting pipe 14. 
Each structural element of the outdoor unit 11 and the indoor unit 12 is 
controlled by a controller 20 provided in the outdoor unit 11. The 
refrigerant compressor 1 is a scroll type compressor for example and the 
indoor unit expander 8 and the outdoor unit expander 6 are structured by 
an electric expansion valve, respectively. 
Data input to the controller 20 are: 
1) a discharge pressure detected by a pressure detector 21 provided at an 
outlet of the refrigerant compressor 1; 
2) a discharge temperature detected by a discharge temperature sensor 23; 
3) an outside air temperature detected by an outside air temperature sensor 
22; 
4) a temperature of heat-exchanger fluid of the outdoor unit detected by a 
heat-exchanger fluid temperature sensor 24 attached to the outdoor unit 
heat exchanger 4; 
5) a blowoff temperature detected by a blowoff temperature sensor 25 of the 
indoor unit provided near a blowoff opening of the indoor unit 12; 
6) a suction temperature detected by a suction temperature sensor 26 of the 
indoor unit provided near a suction opening of the indoor unit 12 or 
within a room in which the air conditioner is installed; 
7) a liquid level detected by a level gauge 30a attached to the accumulator 
2; and 
8) a liquid level detected by a level gauge attached to the receiver 7. 
FIG. 2 is a longitudinal section view illustrating an internal structure of 
the receiver used in the embodiment shown in FIG. 1, wherein a partition 
plate erects from the bottom of a container 50 and refrigerant lead-out 
and lead-in pipes 51a and 51b are introduced to each chamber partitioned 
by the partition plate. Refrigerant is charged in the container 50 
exceeding the top of the partition plate. 
A vapor compressing refrigeration cycle is created in the air conditioner 
described above and as the refrigerant thereof, it uses non-azeotrophic 
refrigerant mixtures in which at least more than two kinds of substances 
having different boiling points are mixed. 
The non-azeotrophic refrigerant mixtures is R407C (ASHRAE refrigerant No.) 
for example in which difluoromethane (HFC 32), pentafluoroethane (HFC 125) 
and 1,1,1,2-tetrafluoroethane (HFC 134a) are mixed in the ratio of 
23:25:52 (weight %). In the refrigerant R407C, the HFC 134a is a higher 
boiling point refrigerant and the HFC 32 and HFC 125 are lower boiling 
point refrigerants. 
When only the HFC 32 and the HFC 125 are mixed, they have an 
anon-azeotrophic point and have a property that their boiling points are 
relatively close. 
In the gas-liquid equilibrium state of R407C which is tertiary refrigerant 
mixtures, the HFC 32 and HFC 125 which have lower boiling points exist on 
the gas side in the ratio more than the mixed ratio and the HFC 134a which 
has a higher boiling point exists on the liquid side in the ratio more 
than the mixed ratio. 
Further, an amount of refrigerant more than an amount of that necessary for 
the adequate operation of the refrigerating cycle is charged. 
The operation and effect of the embodiment described above will be 
explained below. 
At first, the normal cooling operation will be explained. When the 
refrigerant compressor 1, the outdoor unit fan 5 and the indoor unit fan 
10 are started, the high temperature and high pressure refrigerant 
compressed by the refrigerant compressor 1 flows into the outdoor unit 
heat exchanger 4 via the four-way valve 3 and is condensed as its heat is 
exchanged with air. Then, it passes through the outdoor unit expander 6 
(the electric expansion valve) which is fully opened. 
However, because almost no pressure is lost in the state when the outdoor 
unit expander 6 is fully opened, the refrigerant flows into the receiver 7 
without changing its state almost at all. Passing through the receiver 7, 
the refrigerant reaches to the indoor unit expander 8 via the liquid 
refrigerant connecting pipe 14, where it is decompressed and is put into a 
low pressure two-phase state. 
Next, the refrigerant evaporates as heat exchange with the room air is 
performed in the indoor unit heat exchanger 9. 
Here, the restriction of the outdoor unit expander 6 is set so that a 
dryness of the refrigerant at the outlet of the indoor unit heat exchanger 
9 becomes a predetermined value. 
The evaporated gas refrigerant flows into the accumulator 2 from the gas 
refrigerant connecting pipe 13 via the four-way valve 3 and returns to the 
refrigerant compressor 1. This operation is repeated thereafter. 
During this operating state, while the refrigerant contains a few bubbles 
at the inlet of the receiver 7 and its dryness is almost zero, the bubble 
level gas is condensed by the heat radiating effect of the receiver 7. As 
a result, a balance of flow mount is taken between the gas refrigerant and 
the liquid refrigerant at the outlet and inlet of the receiver so that the 
dryness of the refrigerant at the outlet of the receiver becomes zero. 
This adjustment causes the excessive refrigerant to be stored in the 
receiver 7, removing almost all the excessive refrigerant from the 
accumulator 2. Thereby, the refrigerating cycle may be stabilized. 
Further, because the composition of the excessive refrigerant present in 
the receiver 7 barely changes, the composition of the refrigerant 
circulating in the refrigerating cycle is not changed significantly from 
the composition when it has been charged. 
Next, the operation and effect when the composition of the refrigerant 
circulating in the refrigerating cycle is changed so that the HFC 32 and 
HFC 125 which are the lower boiling point refrigerants increase will be 
explained below. 
When the controller 20 determines that the composition should be changed 
based on an outside air temperature or the like detected by the outside 
air temperature sensor 22, the controller 20 issues a signal restricting 
the restriction of the outdoor unit expander 6. 
When the restriction thereof is restricted, the refrigerant at the inlet of 
the receiver 7 is put into a saturation state, becoming a gas-liquid 
two-phase flow. Due to that, the balance of the gas-liquid flow amount of 
the refrigerant flowing in or out of the receiver 7 is lost. The gas 
refrigerant flowing into the receiver 7 pushes down the liquid level and 
the excessive refrigerant held within the container of the receiver 7 is 
released into the refrigerating cycle. 
The released excessive refrigerant passes sequentially through the indoor 
unit expander 8, the indoor unit heat exchanger 9 and the gas refrigerant 
connecting pipe 13 and flows into the accumulator 2. The controller 20 
transmits a signal for opening the restriction of the indoor unit expander 
8 in response to the operation of the outdoor unit expander 6 to the 
indoor unit expander 8. Then, the controller 20 controls the refrigerant 
at the outlet of the indoor unit heat exchanger 9 so that it becomes wet, 
not completely gasifying it. 
Thereby, the refrigerant flowing into the accumulator 2 is put into the 
gas-liquid two-phase state and the dryness thereof becomes large. In the 
gas refrigerant within this two-phase state refrigerant, the lower boiling 
point refrigerants having a higher capacity is increased. 
Various items of the accumulator 2 at the side for outputting the 
refrigerant, such as diameters of an oil returning orifice and a gas 
refrigerant lead-out orifice, are designed to have a size which permits 
the excessive refrigerant flowing into the accumulator 2 to be stored. 
Thereby, the liquid refrigerant in which HFC 134a which is the higher 
boiling point refrigerant is increased is stored in the accumulator 2. The 
refrigerant circulating within the refrigerating cycle is changed so that 
the lower boiling point refrigerants composed of the HFC 32 and HFC 125 
having high capacity thermophysical properties are increased in contrary, 
it is put into a high pressure state. Accordingly, the refrigerating cycle 
is operated by the composition of the refrigerant having the higher 
capacity, thus enhancing the cooling capacity of the air conditioner. 
Next, the heating operation will be explained. 
During the heating operation, the four-way valve 3 is switched and the 
refrigerant circulates through, in an order of, the refrigerant compressor 
1, the four-way valve 3, the gas refrigerant connecting pipe 13, the 
indoor unit heat exchanger 9, the indoor unit expander 8, the liquid 
refrigerant connecting pipe 14, the receiver 7, the outdoor unit expander 
6, the outdoor unit heat exchanger 4, the four-way valve 3 and the 
accumulator 2. Because the indoor unit expander 8 is normally fully 
opened, the opening of the indoor unit expander 8 is restricted to put the 
refrigerant into the saturated two-phase state at the inlet of the 
receiver 7 when the ratio of the composition of the lower boiling point 
refrigerant is increased. Then, the excessive refrigerant is moved to the 
accumulator 2 via the outdoor unit heat exchanger 4 and the four-way valve 
3. 
The operation described above is the same with the case of the cooling 
operation and thereby, the heating capacity can be enhanced. 
Next, a second embodiment of the present invention will be explained. The 
system structure is the same with that of the air conditioner of the first 
embodiment, except of that a receiver shown in FIG. 3 is used instead of 
the receiver 7. In the receiver 7a of the present embodiment, a partition 
plate erects from the bottom of a container 50 and refrigerant lead-out 
and lead-in pipes 51a and 51b are introduced to each chamber partitioned 
by the partition plate. Gas refrigerant mixing holes 52a and 52b are 
created through each of the refrigerant lead-out and lead-in pipes. The 
refrigerant is charged in the container 50 exceeding the top of the 
partition plate. 
The operation and effect of the second embodiment will be explained. In the 
receiver 7a of the present embodiment, gas refrigerant suctioned from the 
gas refrigerant mixing hole (either the hole 52a or 52b) located at the 
upper part of the refrigerant lead-out/lead-in pipe on the side from which 
the refrigerant flows out (either the pipe 51a or 51b as cooling and 
heating is switched) and liquid refrigerant pulled up from the lower part 
of the container 50 by the refrigerant lead-out/lead-in pipe are mixed to 
put the refrigerant at the outlet of the receiver 7a into a gas-liquid 
two-phase state having a predetermined dryness. 
During the normal operation, the controller 20 decides an opening of both 
of the expander at the inlet side of the receiver 7a (the outdoor unit 
expander 6 during the cooling operation and the indoor unit expander 8 
during the heating operation) and the expander at the outlet side of the 
receiver 7a (the indoor unit expander 8 during the cooling operation and 
the outdoor unit expander 6 during the heating operation) so that the 
dryness of the refrigerant at the inlet of the receiver 7a becomes a 
predetermined dryness. Then, the balance of the amount of refrigerant 
flowing out of or flowing into the receiver 7a is kept to stabilize the 
liquid level of the refrigerant within the receiver 7a and to assure the 
excessive refrigerant. 
Thereby, as a result of the expansion in the indoor unit expander 8 during 
the heating operation, the excessive refrigerant is held within the 
receiver 7a even when the refrigerant is put into the saturated two-phase 
state at the inlet of the receiver 7a and the refrigerant flowing through 
the liquid refrigerant connecting pipe 14 is always put into the saturated 
two-phase state, so that the amount of refrigerant charged into the 
refrigerating system may be reduced. Further, because the dryness is 
small, the change in the composition of the excessive refrigerant is 
small. 
Next, the operation for changing the composition of the refrigerant 
circulating in the refrigerating cycle in the second embodiment will be 
explained. 
When the composition of the refrigerant is changed so that the HFC 32 and 
HFC 125 which are the lower boiling point refrigerants increase more than 
the ratio at the time of charge, the opening of the expander (the outdoor 
unit expander 6 during the cooling operation and the indoor unit expander 
8 during the heating operation) before the receiver 7a is reduced and the 
opening of the expander (the indoor unit expander 8 during the cooling 
operation and the outdoor unit expander 6 during the heating operation) at 
the outlet side of the receiver 7a is increased, similarly to the first 
embodiment. 
It increases the dryness of the refrigerant at the inlet of the receiver 7a 
and allows the excessive refrigerant within the receiver 7a to be flown 
out to the refrigerating cycle. That is, the pressure within the receiver 
7a which is at the intermediate point between a condensing pressure and an 
evaporating pressure can be changed by controlling the expanders provided 
at the inlet and outlet sides of the receiver 7a in an associated manner. 
Thus the dryness in the receiver 7a changes and the amount of the gas 
refrigerant flowing into the receiver 7a increases, moving the refrigerant 
within the receiver 7a to the accumulator 2, so that the composition of 
the refrigerant circulating within the refrigerating cycle may be changed 
in the same manner with the first embodiment. 
As described above, the present embodiment allows the composition of the 
circulating refrigerant to be arbitrarily changed, the amount of 
refrigerant to be reduced and the operation wherein the capacity of the 
refrigerating system is increased to be realized. 
FIG. 4 shows a variation of the second embodiment, wherein only a receiver 
7b is modified. The receiver 7b has a structure in which the receiver 7a 
in the second embodiment is turned upside down. Refrigerant lead-out and 
lead-in pipes 51a and 51b are provided at the lower part of the container 
50. Liquid refrigerant stored in the lower part of the container is 
suctioned up from liquid refrigerant mixing holes 53a and 53b provided on 
the respective refrigerant lead-out and lead-in pipes to mix with gas 
refrigerant suctioned from the ends of the refrigerant lead-out and 
lead-in pipes 51a and 51b to turn into a two-phase flow. 
The use of this receiver 7b allows the same operation and effect with the 
second embodiment to be obtained. 
When the composition of the circulating refrigerant is changed so as to 
increase the lower boiling point refrigerant, the controller 20 generates 
a signal for changing the composition of the refrigerant when an outside 
air temperature or a temperature of air suctioned to the heat exchanger 
reaches to a set value in any of the embodiments described above. 
When the capacity is enhanced by changing the composition of the 
refrigerant, an operating pressure is increased as well. Due to that, when 
a condensation temperature is high, i.e. when an outside air temperature 
is high while the cooling operation is performed or when a room 
temperature is high while the heating operation is performed, it is 
necessary to provide means for restricting a refrigerant pressure so that 
it will not exceed a designed pressure of the equipment in advance. 
Then, the restricting means will be explained below with reference to a 
flow chart of the control in the first embodiment shown in FIG. 5. 
When a value of a temperature detected by the outside air temperature 
sensor 22 or the indoor unit suction temperature sensor 26 is lower than a 
set temperature during the operation of the refrigerating system, the 
opening of the outdoor unit expander 6 and the indoor unit expander 8 is 
changed to change the composition of the refrigerant circulating within 
the refrigerating cycle. 
A variation of the composition may be detected by using liquid level 
detecting means of the accumulator 2 or circulating composition detecting 
means and the controller 20 decides the opening of the expanders so that 
the composition of the refrigerant turns into a predetermined composition. 
The control described above for increasing the lower boiling point 
refrigerant within the circulating refrigerant may be eliminated by 
monitoring each structural equipment so that they will not deviate their 
operating limit by using a pressure detector 21 using a pressure sensor or 
a pressure switch, a discharge temperature sensor 23 and the indoor unit 
blowoff temperature sensor 25, etc. 
During the defrosting operation, the refrigerant flow direction is the same 
as that during the cooling operation. As described in the explanation of 
the cooling mode, the refrigeration cycle is operated by the composition 
of the refrigerant having the higher capacity to enhance the cooling 
capacity. Therefore the defrosting operation may be finished in a short 
time, thus enhancing the comfortableness, by incorporating the control for 
changing the composition in the defrosting operation for removing frost of 
the outdoor unit heat exchanger 4 during the heating operation. 
As described above, the present invention makes the complicated structure 
such as the rectifier unit and the control method thereof unnecessary and 
allows the composition of the refrigerant circulating within the 
refrigerating cycle to be changed just by using the structural elements 
which the refrigerating cycle is conventionally equipped with. 
Accordingly, the refrigerating cycle may be operated by way of the ratio 
of composition of the refrigerant, which has been unable to be used due to 
the restriction on the pressure level of the system in the past. 
Specifically, because the refrigerating cycle can be shifted to the 
operation of increasing the lower boiling point refrigerant, the capacity 
of the air conditioner may be enhanced by the mechanism at low cost. 
Further, because it is a simple mechanism, it requires no complicated 
control, providing a stable refrigerating cycle and improving the 
reliability of the equipments. 
Still more, it allows the reduction of the amount of refrigerant charged, 
the reduction of the cost of each structural equipment of the 
refrigerating cycle, the reduction of an amount of the refrigerant 
released to the, atmosphere to the minimum when the system is decomposed 
or adjusted and the elimination of the cause of the global warming and the 
environmental pollution.