Method of testing the purity of refrigerant flowing through a refrigeration system

A refrigeration system having a refrigerant compressor which has a refrigerant purity sampling circuit in parallel fluid flow communication therewith. The purity sampling circuit includes a refrigerant purity tube holder in which a refrigerant purity tube may be removably supported to thereby cause a flow of refrigerant therethrough during a purity sampling test due to the pressure differential across the compressor. The refrigerant purity sampling holder is adapted to receive an empty open ended test tube therein. The empty tube is left in the holder at all times, except when it is desired to perform a purity sampling test, in which case the empty open tube is removed and an active purity sampling tube is inserted therein. The system is further provided with the capability of purging the empty open ended tube and the refrigerant purity sampling circuit prior to the installation of an active tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to refrigerant recovery and purification systems. 
More specifically it relates to an arrangement for testing the purity of 
the refrigerant which has been recovered and purified by such a system. 
2. Description of The Prior Art 
A wide variety of mechanical refrigeration systems are currently in use in 
a wide variety of applications. These applications include domestic 
refrigeration, commercial refrigeration, air conditioning, dehumidifying, 
food freezing, cooling and manufacturing processes, and numerous other 
applications. The vast majority of mechanical refrigeration systems 
operate according to similar, well known principals, employing a 
closed-loop fluid circuit through which a refrigerant flows. A number of 
saturated fluorocarbon compounds and azeotropes are commonly used as 
refrigerants in refrigeration systems. Representative of these 
refrigerants are R-12, R-22, R-500 and R-502. 
Those familiar with mechanical refrigeration systems will recognize that 
such systems periodically require service. Such service may include 
removal, of, and replacement or repair of, a component of the system. 
Further during normal system operation the refrigerant can become 
contaminated by foreign matter within the refrigeration circuit, or by 
excess moisture in the system. The presence of excess moisture can cause 
ice formation in the expansion valves and capillary tubes, corrosion of 
metal, copper plating and chemical damage to insulation in hermetic 
compressors. Acid can be present due to motor burn out which causes 
overheating of the refrigerant. Such burn outs can be temporary or 
localized in nature as in the case of a friction producing chip which 
produces a local hot spot which overheats the refrigerant. The main acid 
of concern is HCL but other acids and contaminants can be produced as the 
decomposition products of oil, insulation, varnish, gaskets and adhesives. 
Such contamination may lead to component failure or it may be desirable to 
change the refrigerant to improve the operating efficiency of the system. 
When servicing a refrigeration system it has been the practice for the 
refrigerant to be vented into the atmosphere, before the apparatus is 
serviced and repaired. The circuit is then evacuated by a vacuum pump, 
which vents additional refrigerant to the atmosphere, and recharged with 
new refrigerant. This procedure has now become unacceptable for 
environmental reasons, specifically, it is believed that the release of 
such fluorocarbons depletes the concentration of ozone in the atmosphere. 
This depletion of the ozone layer is believed to adversely impact the 
environment and human health. Further, the cost of refrigerant is now 
becoming an important factor with respect to service cost, and such a 
waste of refrigerant, which could be recovered, purified and reused, is no 
longer acceptable. 
To avoid release of fluorocarbons into the atmosphere, devices have been 
provided that are designed to recover the refrigerant from refrigeration 
systems. The devices often include means for processing the refrigerants 
so recovered so that the refrigerant may be reused. Representative 
examples of such devices are shown in the following U.S. Pat. Nos.: 
4,441,330 "Refrigerant Recovery And Recharging System" to Lower et al; 
4,476,688 "Refrigerant Recovery And Purification System" to Goddard; 
4,766,733 "Refrigerant Reclamation And Charging Unit" to Scuderi; 
4,809,520 "Refrigerant Recovery And Purification System" to Manz et al; 
4,862,699 "Method And Apparatus For Recovering, Purifying and Separating 
Refrigerant From Its Lubricant" to Lounis; 4,903,499 "Refrigerant Recovery 
System" to Merritt; and 4,942,741 "Refrigerant Recovery Device" to Hancock 
et al. 
Following the operation of such systems to recover and purify refrigerant, 
it is desirable, before reusing the refrigerant, to test the purity of 
that refrigerant. At best, existing systems are provided with sight 
glasses which may give some indication of the present of moisture in the 
recovered refrigerant. 
U.S. Pat. No. 4,923,806 entitled "Method and Apparatus for Refrigerant 
Testing In A Closed System" is assigned to the assignee of the present 
invention and is directed to a method and apparatus for detecting 
contaminants in a refrigerant medium. This patent teaches the use of 
single use transparent glass testing tubes which are sealed until used and 
which contain therein an oil removal section, a water removal and 
indicating section, and, an acid indicating section. In use, the ends of 
the glass testing tubes are broken off and the tube is placed in a tube 
holder apparatus which functions to seal the tube so that all of the 
refrigerant flows directed through the tube. The presence of contaminants 
is indicated by a color change which may be quantified by comparison to a 
color chart and/or the extent of the promulgation of the color change in 
the indicating media. The refrigerant sample is allowed to pass through 
the testing tube and then to the atmosphere. The venting of refrigerant 
gas to the atmosphere is not considered to be environmentally acceptable 
expedient. 
A commonly assigned U.S. patent application, Ser. No. 612,641, filed on 
Nov. 13, 1990, discloses a system for sampling the purity of refrigerant 
flowing through a refrigeration circuit. This system makes use of the 
system of U.S. Pat. No. 4,923,806, described above. The system described 
in the above identified patent application is shown as applied to a 
refrigerant recovery and purification system. In that system the operator 
had two options with respect to the refrigerant purity sampling feature. 
The first option was not to select this mode of operation, in which case 
the sampling tube fixture may or may not contain a refrigerant quality 
testing tube. Accordingly, the fixture could be open to the atmosphere. 
The second option was to select the refrigerant purity sampling feature. 
In that case, the user was instructed to install a purity test tube into 
the fixture prior to the recovery/recycle operation, and, the unit was 
programmed to automatically perform the purity test at the end of the 
cycle selected. 
It has been found that, particularly with more sensitive sampling tubes, 
moisture in the surrounding air, moisture in the tube holder, and/or 
moisture from previous refrigerant samples, has adversely affected the 
accuracy and repeatability of moisture level reading in this system. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a refrigerant purity 
test system for a refrigeration system which minimizes the effects of 
external moisture on the results of the purity test. 
It is a further object of the present invention to incorporate a 
refrigerant purity test system into a refrigerant recovery and 
purification system in a manner which assures that the refrigerant tested 
by a purity test system is representative of the refrigerant circulating 
in the recovery system. 
These and other objects of the invention are achieved in a refrigeration 
system having a refrigerant compressor which has a refrigerant purity 
sampling circuit in parallel fluid flow communication therewith. The 
purity sampling circuit includes a refrigerant purity tube holder in which 
a refrigerant purity tube may be removably supported to thereby cause a 
flow of refrigerant therethrough during a purity sampling test due to the 
pressure differential across the compressor. The refrigerant purity 
sampling holder is adapted to receive an empty open ended test tube 
therein. The empty tube is left in the holder at all times, except when it 
is desired to perform a purity sampling test, in which case the empty open 
tube is removed and an active purity sampling tube is inserted therein. 
The system is further provided with the capability of purging the empty 
open ended tube and the refrigerant purity sampling circuit prior to the 
installation of an active tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An apparatus for recovering and purifying the refrigerant contained in a 
refrigeration system is generally shown at reference numeral 10 in FIG. 1. 
The refrigeration system to be evacuated is generally indicated at 12 and 
may be virtually any mechanical refrigeration system. 
As shown the interface or tap between the recovery and purification system 
10 and the system being serviced 12 is a standard gauge and service 
manifold 14. The manifold 14 is connected to the refrigeration system to 
be serviced in a standard manner with one line 16 connected to the low 
pressure side of the system 12 and another line 18 connected to the high 
pressure side of the system. A high pressure refrigerant line 20 is 
interconnected between the service connection 22 of the service manifold 
and a T connection 11 for coupling the line 20 to the recovery system 10. 
Located in the interconnecting line 20 is a filter-dryer 13 which is 
mounted external of the recovery system. This device as will be seen, is 
normally installed in the line 20 only when the system is to be operated 
first in the liquid recovery mode of operation. 
The recovery system 10 includes two sections, as shown in FIG. 1 the 
components and controls of the recovery system are contained within a self 
contained compact housing (not shown) schematically represented by the 
dotted line 24. A refrigerant storage section of the system is contained 
within the confines of the dotted lines 26. The details of each of these 
sections and their interconnection and interaction with one another will 
now be described in detail. 
As will be appreciated as the description of the operation of the system 
continues there are two refrigerant paths extending from the T-connection 
11 at the end of interconnecting line 20. The first path, i.e. the liquid 
path, extends to the left of the T-11 to an electrically actuatable 
solenoid valve SV7. This valve will selectively allow refrigerant to pass 
therethrough when actuated to its open position or will prevent the flow 
of refrigerant therethrough when electrically actuated to its closed 
position. Additional electrically actutatable solenoid valves contained in 
the system operate in the same conventional manner. From SV7 a liquid 
refrigerant line 15 extends to the refrigerant storage section of the 
system 26 where it communicates through a valve 90 with a refrigerant 
storage cylinder 86. In the liquid recovery mode of operation of the 
system liquid refrigerant passes through the line 15 directly from the 
refrigeration system 12 to the storage cylinder 86. 
When the system is operated in the vapor recovery mode gaseous refrigerant 
flowing through the interconnecting line 20 flows through the T-11 and to 
the right to electrically actuatable solenoid valve SV3. From SV3 
refrigerant flows via conduit 28, through a check valve 98 and a 
T-connection 17 to another T-connection 19. From the T-19 a conduit 30 
conducts the refrigerant to the inlet of a combination accumulator/oil 
trap 32 having a drain valve 34. Refrigerant gas is then drawn from the 
oil trap through conduit 36 to an acid purification filter-dryer 38 where 
impurities such as acid, moisture, foreign particles and the like are 
removed before the gases are passed via conduit 40 to the suction port 42 
of the compressor 44. A suction line accumulator 46 is disposed in the 
conduit 42 to assure that no liquid refrigerant passes to the suction port 
42 of the compressor. The compressor 44 is preferably of the rotary type, 
which are readily commercially available from a number of compressor 
manufacturers but may be of any type such as reciprocating, scroll or 
screw. 
From the compressor discharge port 48 gaseous refrigerant is directed 
through conduit 50 to a conventional float operated oil separator 52 where 
oil from the recovery system compressor 44 is separated from the gaseous 
refrigerant and directed via float controlled return line 54 to a 
T-connection 21. From the T-21, the oil passes via conduit 23 to the 
conduit 40 which communicates with the suction port of the compressor. 
From the outlet of the oil separator 52 gaseous refrigerant passes via 
conduit 56 to the inlet 58 of a heat exchanger/condenser coil 60. An 
electrically actuated condenser fan 62 is associated with the coil 60 to 
direct the flow of ambient air through the coil as will be described in 
connection with the operation of the system. 
From the outlet 64 of the condenser coil 60 an appropriate conduit 66 
conducts refrigerant to a T-connection 68. From the T 68 one conduit 70 
passes to another electrically actuated solenoid valve SV4 while the other 
branch 72 of the T passes to a suitable refrigerant expansion device 74. 
In the illustrated embodiment the expansion device 74 is a capillary tube 
and a strainer 76 is disposed in the refrigerant line 72 upstream from the 
capillary tube to remove any particles which might potentially block the 
capillary. It should be appreciated that the expansion device could 
comprise any of the other numerous well known refrigerant expansion 
devices which are widely commercially available. The conduit 72 containing 
the expansion device 74 and the conduit 70 containing the valve SV4 rejoin 
at a another T connection 78 downstream from both devices. It will be 
appreciated that the solenoid valve SV4 and the expansion device 74 are in 
a parallel fluid flow relationship. As a result, when the solenoid valve 
SV4 is open the flow of refrigerant will be, because of the high 
resistance of the expansion device, through the solenoid valve in a 
substantially unrestricted manner. On the other hand, when the valve SV4 
is closed, the flow of refrigerant will be through the high resistance 
path provided by the expansion device. Combination devices such as 
electronically actuated expansion valves are known which would combine the 
functions of the valves SV4 and the capillary tube 74, however, as 
configured and described above, the desired function is obtained at a 
minimum cost. 
From the T-78 a conduit 80 passes to an appropriate coupling (not shown) 
for connection of the system as defined by the confines of the line 24, 
via a flexible refrigerant line 82 to the inlet port 84 of the previously 
referred to refillable refrigerant storage container 86. The conduit 80 
contains a check valve 25 which is adapted to allow flow only in the 
direction from the T-78 to the storage cylinder 86. The container 86 is of 
conventional construction and includes a second port 88 adapted for vapor 
outlet. The storage cylinder 86 further includes a liquid level indicator 
92. The liquid level indicator, for example, may comprise a compact 
continuous liquid level sensor of the type available from Imo Delaval 
Inc., Gems Sensors Division. Such an indicator is capable of providing an 
electrical signal indicative of the level of the refrigerant contained 
within the storage cylinder 86. 
Refrigerant line 94 interconnects the vapor outlet 88 of the cylinder 86 
with the T connection 76 in the conduit 28. An additional electrically 
actuated solenoid valve SV1 is located in the line 94. 
With continued reference to FIG. 1 a refrigerant purity sampling circuit 
100 is included in the system in a parallel fluid flow arrangement with 
the compressor 44. The purity sampling circuit 100 includes an inlet 
conduit 102 in fluid communication with the inlet conduit 50 of the oil 
separator 52. The inlet conduit 102 has an electrically actuated solenoid 
valve SV6 disposed there along and from there passes to the inlet of a 
sampling tube holder 110. The outlet of the sampling tube holder 104 is 
interconnected via conduit 106 with T-21, conduit 23, and with the conduit 
40 which communicates with the suction port 42 of the compressor. An 
electrically controlled solenoid valve SV5 is disposed in the conduit 106. 
The conduit section 23 is also provided with a T-connection 27. The T-27 is 
connected via a refrigerant sampling conduit 29 to the T-connection 19 in 
conduit 28. A normally closed solenoid actuated flow control valve SV2 is 
located in the conduit 29. 
The solenoid valves SV5 and SV6, when closed, isolate the sampling tube 
holder 104 from the system and allow easy replacement of the sampling tube 
contained therein. The sampling tube holder is preferably of the type 
illustrated in FIGS. 9 and 10. Such a holder is described and claimed in 
commonly assigned U.S. patent application Ser. No. 612,639, filed on Nov. 
13, 1990. 
Referring now to FIGS. 9 and 10 the sampling tube holder 110 the includes a 
supporting base 112, a fixed end fitting 114, a movable end fitting 116, 
and, an interconnecting biassing spring 118. 
The structure of the base 112 takes on the appearance of a rail in that it 
comprises two parallel extending, inverted L shaped sections 120 which are 
interconnected by a central web like portion 122 which is shorter than the 
section 120. The base essentially defines an elongated H shape as viewed 
from the top with the legs being longer at the right hand end of the base 
upon which the moveable end fitting 116 is mounted. Four elongated 
mounting slots 124 are provided, two in each rail, to facilitate ease of 
mounting of the fixture. 
The end fittings 114 and 116 are substantially identical each having a main 
body portion 124 and a mounting portion 126 which extends from the lower 
end of the body and defines an inverted T shaped cross section. The two 
laterally extending legs 128 of the mounting portion are adapted to be 
received in sliding relationship with mating channel like surfaces 130 
defined by the inverted L shaped portions of the legs forming the ends of 
the base 112. The lower surface 132 of the main body portion rests on the 
top of the rails 120. The fixed end fitting 114 is appropriately fastened 
to the base 112 for example by a suitable adhesive. 
The moveable end fitting 116 is slideably received in the end of the base 
112 having the longer legs and as will be seen is moveable axially with 
respect to the base as depicted in FIG. 1. Each of the end fittings 114 
and 116 is provided with a spring anchor device 134 mounted on the upper 
side of the T shaped mounting extension 126. The longitudinally extending 
tension spring 118 having suitable anchoring loops 138 at each end engages 
the anchor devices 134 of both the fixed and moveable end fittings. The 
length of the spring is such that when anchored to both end fittings 114, 
116 as depicted in FIG. 1 a substantial force is exerted on the moveable 
end fitting to the left. This force is critical to obtaining and 
maintaining the seal between the fixture and the sampling tube 140 mounted 
therein as will be appreciated as the engagement of the end fittings 114 
and 116 with the sampling tube is described. 
Each of the end fittings 114 and 116 has a flow path defined therethrough 
which includes an internal channel 142 interconnected by a pair of 
threaded fittings. A first threaded flow fitting 144 is mounted to the 
mounting extension 126. In the illustrated embodiment each of the fittings 
144 is provided with a standard 1/4 inch flare fitting to facilitate 
attachment to appropriate flow conduits in a testing system. 
A second set of fittings 146 which define the sampling tube support and 
seal configuration are mounted in the bodies 124 of the end fittings 114 
and 116 such that they are in confronting axially aligned relationship 
with one another when the device is assembled. Each of the fittings 146 
defines a standard 1/4 inch flare fitting upon which a 1/4 inch flare cap 
148 with a 1/4 inch diameter hole drilled therein is threadably engaged. A 
cylindrical rubber seal 150 is disposed within each of the flare caps 148 
as shown in the broken away view of the seal arrangement on the moveable 
end fitting 116 in FIG. 1. 
The seal 150 is inserted into the flare cap 148, prior to assembly of the 
cap to flare fitting, through the opening adjacent to the threaded end. 
When the cap 148 is threaded into the fitting the seal is retained between 
the fitting and an annular lip 151 formed at the end of the flare cap 148. 
As thus described a sample tube 140 is installed within the fixture 110 by 
first breaking off ends of the glass sample tube, pulling back the 
moveable end fitting 116 an appropriate distance to allow one end of the 
sampling tube to be inserted into engagement with the seal fitting 146 of 
the fixed end fitting 114, and, while holding the tube in proper 
alignment, allowing the moveable fixture 116 to move, under the force of 
the spring, into appropriate sealing engagement with the other end of the 
sampling tube. As thus installed the flare fittings and the seal elements 
150 inside the flare cap 148, in combination with the constant tension 
provided by the spring, establish a leak proof path through the fixture. 
In the preferred embodiment the spring is selected to maintain a constant 
five pounds of tension against the seals 150 which will allow a pressure 
maximum of over 200 psi before leakage occurs around the seal. It should 
be appreciated that the rubber seals may, with continued use, lose there 
sealing integrity as they are subject to damage by the rough ends of the 
sampling tube 140. The seals 150 may be readily removed and replaced with 
new ones as the flare caps may be unscrewed by hand and a new rubber seal 
installed as necessary. 
Automatic control of all of the components of the refrigerant recovery 
system 10 is carried out by an electronic controller 108 which is formed 
of a micro-processor having a memory storage capability and which is 
micro-programmable to control the operation of all of the solenoid valves 
SV1 through SV7 as well as the compressor motor and the condenser fan 
motor. Inputs to the controller 108 include a number of measured or sensed 
system control parameters. These control parameters may include the 
temperature of the storage cylinder Tstor which comprises a temperature 
transducer capable of accurately providing a signal indicative of the 
temperature of the refrigerant in the storage cylinder 86. Ambient 
temperature is measured by a temperature transducer positioned at the 
inlet to the condenser coil or condenser fan 62 and is referred to as 
Tamb. The temperature of the refrigerant flowing through the compressor 
discharge line 50 is sensed by a temperature transducer 110 positioned on 
the compressor discharge line 50. 
Of great importance in the control scheme of the system is the compressor 
suction pressure designated as P2 and the compressor discharge pressure 
designated as P3. As indicated in FIG. 1 a pressure transducer labeled P2 
is in fluid flow communication with the suction line 40 to the compressor 
while a second pressure transducer P3 is in fluid communication with the 
high pressure refrigerant line 56 passing to the condenser. The pressure 
ratio across the compressor 44 is defined as the ratio P3/P2. An 
additional input to the controller 108 is the signal from the liquid level 
indicator 92. 
Looking now at FIG. 7 it will be noted that the operating modes of the 
system are identified and the condition of the electrically actuatable 
components of the system are shown in the different modes. In the Standby 
mode the system has been turned on and all electrically actuatable 
mechanical systems are de-energized and ready for operation. In the 
Service mode, the electrically actuated solenoid valves SV1 through SV4 
and SV7 are all open thereby equalizing the pressures within the system so 
that it may be serviced without fear of encountering high pressure 
refrigerant. 
The liquid recovery mode will now be described in detail in connection with 
the flow chart of FIG. 2A. It should be appreciated that the liquid 
recovery mode is designed to be used in larger systems for example systems 
having a refrigerant charge of greater than 5 pounds of refrigerant. In 
systems where less than 5 pounds of refrigerant are contained in the 
system the liquid recover mode of operation may be omitted and the 
operator may go directly to the vapor recover cycle which will be 
subsequently described. 
At this point it is assumed that a system containing greater than 5 pounds 
of refrigerant is being serviced and that the device 10 has been coupled 
to the system 12 for removal of refrigerant therefrom. With reference now 
to FIG. 2A and FIG. 7 it will be seen that upon initiation of the Liquid 
Recover mode the controller 108 will open valves SV1, and SV7. The valves 
SV2, SV3, SV4, SV5 and SV6 will remain closed. Valves SV5 and SV6 as noted 
in FIG. 7 operate together as a single output from the microprocessor 
(controller 108) and the only time these valves are open is when the 
contaminant testing process is being carried out. These valves will not be 
discussed further in connection with other modes of operation of the 
system. The motors of the compressor 44 and the condenser fan 62 are also 
energized upon initiating the liquid recover mode. 
Looking now at operation of the system in the liquid recover mode, and 
referring to FIG. 1. With valve SV3 closed and valve SV7 open refrigerant 
from the system being serviced 12 is forced by the pressure of the 
refrigerant in the system through conduit 20, through the T-11, through 
valve SV7 and via liquid refrigerant line 15 to the valve 90 on the 
refrigerant storage cylinder 86 and directly into refrigerant storage 
cylinder. 
Upon entering the storage cylinder 86 at ambient conditions, a portion of 
the liquid refrigerant will exist in gaseous form. At this time because, 
the solenoid valve SV1 is open, a fluid path is directly established 
between the vapor outlet 88 of the storage cylinder 86 and the conduit 94 
which is in communication with the low pressure side of the compressor 44. 
With the solenoid valve SV4 closed refrigerant passing from the condenser 
60 will pass through the refrigerant expansion device 74. 
Accordingly, with the control solenoids set as described above, during 
liquid recovery, the compressor 44 acts to withdraw low pressure gaseous 
refrigerant directly from the storage cylinder 86. This refrigerant passes 
via conduit 94 and T-96, through the T-17, and conduit 30 to the oil 
separator 32. From the oil separator it passes via conduit 36 to the 
filter drier 38, and thence via conduit 40 and accumulator 46 to the 
compressor 44 which delivers high pressure gaseous refrigerant via conduit 
50 to the oil separator 52. From the oil separator 52 the high pressure 
gaseous refrigerant passes via conduit 56 to the condenser coil 60 where 
the hot compressed gas condenses to a liquid. 
Liquified refrigerant leaves the condensing coil 60, via conduit 66 and 
passes through the T-connection 68 through the strainer 76 and, via 
conduit 72 to the refrigerant expansion device 74. The thus condensed 
refrigerant, at a high pressure, flows through the expansion device 74 
where the refrigerant undergoes a pressure drop, and is at least partially 
flashed to a vapor. The liquid-vapor mixture then flows via conduit 80 and 
82 back to the refrigerant storage cylinder 86 where it evaporates and 
absorbs heat from the refrigerant within the cylinder 86 thereby lowering 
the pressure and temperature within the storage cylinder 86. As a result 
of the lowered temperature and pressure within the storage cylinder 86 the 
pressure differential between the refrigeration system being serviced 12, 
which is at ambient temperature, and the storage tank 86 is substantially 
increased and, as a result the flow of liquid refrigerant through the 
liquid refrigerant line 15 to the storage cylinder is substantially 
increased. 
It will be appreciated, that during this mode of operation refrigerant will 
continue to recirculate through the cooling and purifying circuit 
described above. 
With reference to FIG. 2A it will be seen that the liquid recovery mode is 
run according to the illustrated embodiment, for two minutes at which time 
the system is shifted to the Cylinder Cool cycle. With reference to FIG. 
7, the only difference between the operation of the system in the Cylinder 
Cool cycle and the liquid recovery cycle is that the solenoid value SV7 is 
closed and the system operates in a closed circuit, as described with no 
connection to the system being serviced. As the Cylinder Cool mode of 
operation continues the cylinder temperature continues to drop as the 
refrigerant is continuously circulated through the closed refrigeration 
circuit. Also during this time the refrigerant is passed through the 
refrigeration purifying components, i.e. the oil separator 32 and the 
filter dryer 38, a plurality of times to thereby further purify the 
refrigerant. The system is run in the Cylinder Cool cycle for five minutes 
in order to assure that the temperature and pressure within the storage 
cylinder is reduced such that it is substantially lower than ambient 
temperature. 
At this point, with continued reference to FIG. 2A the system returns to 
the liquid recovery mode of operation. As the second liquid recovery cycle 
continues, the controller 108 continues to receive signals related to a 
number of conditions within the system. Specifically the temperature 
transducer Tstor provides a signal indicative of the temperature of the 
refrigerant in the storage cylinder 86. The pressure transducers P2 and 
P3, provide information with respect to the pressure entering and leaving, 
respectively the compressor 44. These three parameters will collectively 
be referred to as system control parameters. 
FIGS. 3, 4 and 5 illustrate the value of the system control parameters 
Tstor, P3 and P2 respectively as a function of the length of time the 
liquid recovery cycle has been run. With respect to each of these 
graphical representations it will be noted that at the seven minute mark 
each of the parameters increases, then stabilizes and then begins to drop. 
The beginning of the increase of each of the parameters, i.e. the seven 
minute point represents the beginning of the second liquid recovery cycle. 
The point at which each of theses parameters begins to drop has been found 
to be correlatable with the time at which the state of the refrigerant 
being withdrawn from the refrigeration system 12 changes from a liquid 
state to a vapor state. The microprocessor of the controller 108 is 
programmed to terminate the recovery mode of operation automatically when 
one of these selected system control parameters falls a predetermined 
amount below its maximum value. As noted in FIG. 2A Tstor is the preferred 
controlled parameter and in the illustrated embodiment the termination of 
liquid recovery occurs when Tstor drops 5.degree. F. from its maximum 
value. In the case of the control parameter being P2 or P3 a drop of 5 psi 
from the maximum value has been found to cause the shift from liquid 
recovery to vapor recovery to occur at an appropriate time. 
With reference to FIG. 2A it will be seen that at this point the system 
shifts to a Cylinder Cool cycle of operation in order to reduce the 
temperature and pressure of the storage cylinder 86 prior to the beginning 
of a vapor recovery cycle. With continued reference to FIG. 2A, this 
Cylinder Cool mode of operation will terminate when any one of three 
conditions occur; 1) the cylinder temperature, as measured by Tstor falls 
to a level 70.degree. F. below ambient temperature (Tamb), or, 2) when the 
Cylinder Cool mode of operation has run for a duration of 15 minutes, or, 
3) when the cylinder temperature Tstor falls to 0.degree. F. Regardless of 
which of the three conditions triggers termination of the Cylinder Cool 
mode, the result is substantially the same, i.e., the temperature (Tstor) 
of the refrigerant stored in the cylinder 86 is well below ambient 
temperature. At this point the system will shift to a vapor recovery mode 
of operation to complete the withdrawal of the refrigerant from the system 
being serviced. 
The Vapor Recovery and Cylinder Cool modes will now be described in detail 
in connection with the flow chart of FIG. 2B. It should be appreciated 
that a Vapor Recovery cycle may begin under two different sets of 
circumstances; 1) in the case of a system containing more than five pounds 
of refrigerant the Vapor Recovery cycle will follow a previously performed 
liquid recovery cycle of operation; and 2) in the case of a refrigeration 
system containing less than five pounds of refrigerant the Vapor Recovery 
cycle represents the initiation of the recovery sequence. As the 
description of the Vapor Recovery and Cylinder Cool modes proceeds, some 
of the description will be redundant, however, for the sake of a complete 
understanding of the operation of the Vapor Recovery and Cylinder Cool 
modes a complete description from initial hookup to a refrigeration or air 
conditioning system 12 will be given. 
The Vapor Recovery mode is the mode in which the device 10 has been coupled 
to an air conditioning system 12 for removal of refrigerant therefrom in 
the vapor state. Upon initiation of the Recover mode the controller 108 
will open valves SV3 and SV4. Valves SV1, SV2, SV5, SV6 and SV7 will 
remain closed. The compressor 44 and the condenser fan 62 are also 
actuated upon initiation of the Recovery mode. 
Looking now at operation of the system in the Vapor Recovery mode, and 
referring to FIG. 1, with valve SV3 open refrigerant from the system being 
serviced 12 is forced by the pressure of the refrigerant in the system, 
and by the suction created by operation of the compressor 44, through 
conduit 20, through valve SV3, check valve 98, T-17 and conduit 30 to the 
accumulator/oil trap 32. Within the accumulator/oil trap the oil contained 
in the refrigerant being removed from the system being serviced falls to 
the bottom of the trap along with any liquid refrigerant withdrawn from 
the system. Gaseous refrigerant is drawn from the accumulator/oil trap 32 
through the filter dryer 38 where moisture, acid and any particulate 
matter is removed therefrom, and, from there passes via conduit 40, 
through the suction accumulator 46 to the compressor 44. 
The compressor 44 compresses the low pressure gaseous refrigerant entering 
the compressor into a high pressure gaseous refrigerant which is delivered 
via conduit 50 to the oil separator 52. The oil separated from the high 
pressure gaseous refrigerant in the separator 52 is the oil from the 
recovery compressor 44 and this oil is returned via conduit 54 to the 
suction line 40 of the compressor to assure lubrication of the compressor. 
From the oil separator 52 the high pressure gaseous refrigerant passes via 
conduit 56 to the condenser coil 60 where the hot compressed gas condenses 
to a liquid. Liquified refrigerant leaves the condensing coil 60 via 
conduit 66 and passes through the T68 through the open solenoid valve SV4, 
and passes via the liquid lines 80 and 82, to the refrigerant storage 
cylinder 86 through liquid inlet port 84. 
While refrigerant recovery is going on the controller 108 is receiving 
signals from the pressure transducers P3 and P2, calculating the pressure 
ratio P3/P2, and, comparing the calculated ratio to a predetermined value. 
Compressor suction pressure P2 is also being looked at alone and being 
compared to a predetermined Recovery Termination Suction Pressure. As 
shown in FIG. 2, the predetermined Recovery Termination Suction Pressure 
is 4 psia, and if P2 falls below this value the Recover mode is terminated 
and the controller 108 initiates the refrigerant quality test cycle, 
identified as Totaltest. This cycle will be described below following a 
complete description of the other modes of operation. TOTALTEST is a 
registered Trademark of Carrier Corporation for "Testers For Contaminants 
in A Refrigerant". 
The selection of the predetermined recovery termination suction pressure of 
4 psia results from recovery system operation wherein it has been shown 
that a compressor suction pressure, P2, of 4 psia or less results in 
recovery of 98 to 99% of the refrigerant from the system being serviced. 
Achieving this pressure during the first Recover mode cycle is unusual, 
however, it is achievable. As an example, P2 may be drawn down to the 4 
psia termination value in low ambient temperature conditions where the 
condensing coil temperature (which is ambient air cooled) is low enough to 
allow P3 to remain low enough for P2 to reach 4 psia before the pressure 
ratio limit is reached. 
Returning now to compressor pressure ratio, as indicated in FIG. 2B, in the 
illustrated embodiment, when the pressure ratio exceeds or is equal to 16 
the microprocessor in the controller 108 performs what is referred to as 
the Recovery Cycle Test. If the Recovery Cycle just performed is the first 
Recovery Cycle performed and the compressor suction pressure P2 is greater 
than or equal to 10 psia the system will shift to what is known as a 
Cylinder Cool mode of operation. If the Recovery Cycle just performed is a 
second or subsequent recovery cycle and the compressor suction pressure P2 
is less than 10 psia the controller will consider the refrigerant Recovery 
as completed and will initiate the refrigerant contaminant test cycle 
(Totaltest). 
The latter conditions, i.e. second or subsequent recover cycle, and P2 less 
than 10 psia, are conditions that are found to exist at high ambient 
temperatures. For example, such conditions may exist when recovering R-22 
from an air conditioning system at an ambient temperature of 105.degree. 
F. and above. Under such conditions it has been found that attempts to 
reduce the compressor suction pressure P2 to values less than 10 psia are 
counterproductive in that a substantial length of operating time would be 
necessary in order to obtain a very small additional drop in suction 
pressure. Further, it has been found, at these conditions, that shifting 
to the Cylinder Cool mode, which will be described below, also would not 
substantially increase the amount of refrigerant that would ultimately be 
withdrawn from the system and accordingly termination of the Vapor 
Recovery mode and initiation of the refrigerant contaminant test cycle is 
indicated. 
Assuming that the Recovery Cycle Test has indicated that either: it is the 
first recovery cycle, or, the compressor suction pressure P2 is greater 
than or equal to 10 psia, the controller 108 will initiate the Cylinder 
Cool mode of operation. 
In the Cylinder Cool mode, as indicated in FIG. 7, solenoid valve SV1 is 
energized and thereby in the open condition. Solenoid valves SV2, SV3 and 
SV4 are closed, and, the compressor motor and condenser fan motor continue 
to be energized. The Cylinder Cool mode of operation essentially converts 
the system to a closed cycle refrigeration system wherein the refrigerant 
storage cylinder 86 functions as a flooded evaporator. By closing solenoid 
valve SV3 the refrigerant recovery and purification system 10 is isolated 
from the refrigeration system 12 being serviced. The opening of solenoid 
valve SV1 establishes a fluid path between the vapor outlet 88 of the 
storage cylinder 86 and the conduit 28 which is in communication with the 
low pressure side of the compressor 44. The closing of solenoid valve SV4 
routes the refrigerant passing from the condenser 60 through the 
refrigerant expansion device 74. 
With the control solenoids set as described above, in the Cylinder Cooling 
mode of operation the compressor 44 compresses low pressure gaseous 
refrigerant entering the compressor and delivers a high pressure gaseous 
refrigerant via conduit 50 to the oil separator 52. From the oil separator 
52 the high pressure gaseous refrigerant passes via conduit 56 to the 
condenser coil 60 where the hot compressed gas condenses to a liquid. 
Liquified refrigerant leaves the condensing coil 60 via conduit 66 and 
passes through the T-connection 68 through the strainer 76 and, via 
conduit 72, to the refrigerant expansion device 74. The thus condensed 
refrigerant, at a high pressure, flows through the expansion device 74 
where the refrigerant undergoes a pressure drop, and is at least 
partially, flashed to a vapor. The liquid-vapor mixture then flows via 
conduits 78 and 82 to the refrigerant storage cylinder 86 where it 
evaporates and absorbs heat from the refrigerant within the cylinder 86 
thereby cooling the refrigerant. 
Low pressure refrigerant vapor then passes from the storage cylinder 86, 
via vapor outlet port 88, through conduit 94 and solenoid valve SV1 to the 
T connection 96. From there it passes through the check valve 98, T-17, 
conduit 30, the oil separator/accumulator 32, filter dryer 38 and conduit 
40 to return to the compressor 44, to complete the circuit. 
As the Cylinder Cool mode of operation continues, the cylinder temperature, 
as measured by the temperature transducer Tstor, continues to drop as the 
refrigerant is continuously circulated through the closed refrigeration 
circuit. Also during this time the refrigerant is passed through the 
refrigeration purifying components, i.e. the oil separator 32 and the 
filter dryer 38, a plurality of times to thereby further purify the 
refrigerant. 
Referring again to FIG. 2, the Cylinder Cool mode of operation will 
terminate when any one of three conditions occur; 1) the cylinder 
temperature, as measured by Tstor falls to a level 70.degree. F. below 
ambient temperature (Tamb), or, 2) when the Cylinder Cooling mode of 
operation has gone on for a duration of 15 minutes, or, 3) when the 
cylinder temperature Tstor falls to 0.degree. F. Regardless of which of 
the three conditions has triggered the termination of the Cylinder Cool 
mode the result is substantially the same, i.e., the temperature (Tstor) 
of the refrigerant stored in the cylinder 86 is now well below ambient 
temperature. As a result, the pressure within the cylinder, corresponding 
to the lowered temperature is substantially lower than any other point in 
the system. 
When any one of the Cylinder Cool mode termination events occur, the 
controller 108 will shift the system to a second Recover mode of 
operation. In the second Recover mode the solenoid valves, and compressor 
and condenser motors are energized as described above in connection with 
the first Recover mode. Because of the low temperature Tstor that has been 
created in the refrigerant storage cylinder, however, the capability of 
the system to withdraw refrigerant from the unit being serviced, without 
subjecting the recovery compressor to high pressure differentials is 
dramatically increased. 
An understanding of this phenomenon will be appreciated with reference to 
FIG. 1. It will be described by picking up a Recover cycle at the point 
where refrigerant withdrawn from the system being serviced is discharged 
from the compressor 44 and is passing, via conduit 56, to the condenser 
60. At this point the pressure within the system, extending from the 
compressor discharge port 48 through to and including the storage cylinder 
86, is dictated by temperature and pressure conditions within the storage 
cylinder 86. As a result the storage cylinder 86 now effectively serves as 
a condenser with the recovered refrigerant passing as a super- heated 
vapor through the condenser coil, through the solenoid valve SV4 and the 
conduits 80 and 82 to the storage cylinder 86 where it is condensed to 
liquid form. 
It is the dramatically lower compressor discharge pressure P3 experienced 
during a second or subsequent Recover mode (i.e. any Recover mode 
following a Cylinder Cool mode) that allows the recovery compressor 44 to 
draw the system being serviced 12 to a pressure lower than heretofore 
obtainable while still maintaining a permissible pressure ratio across the 
recovery compressor. 
It will be appreciated that in a second Recover mode, the pressure ratio 
P3/P2 could exceed the predetermined value (which in the example given is 
16) and, depending upon the other system conditions, as outlined in the 
flow chart of FIG. 2, will result in an additional Cylinder Cool mode of 
operation or termination. 
With continued reference to FIG. 2B, the system will operate as described 
until conditions exist which result in the controller 108 switching to the 
refrigerant purity test (Totaltest) mode of operation. This mode of 
operation will now be described in detail in connection with a refrigerant 
recovery and purification system, it should be appreciated however that it 
may be desirable to have a refrigerant purity test circuit installed in 
many refrigeration systems in order to facilitate making a check of the 
purity of the refrigerant flowing through the system while it is in 
operation and, without venting any refrigerant to the atmosphere. 
Accordingly, the refrigerant purity test system described herein may be 
readily adapted to virtually any refrigeration system having a compressor. 
Referring now to FIG. 8 a flow chart showing the sequence of steps taken in 
performing the refrigerant purity test is shown. The refrigerant purity 
test feature automatically samples refrigerant for acid and moisture 
contamination. The refrigerant purity test may be used after a recovery 
cycle or a recycle mode of operation. 
The FIG. 8 flow chart describes the system in connection with performance 
of a typical refrigerant recovery operation. Step 160 requires that the 
operator install, in the sampling tube holder 110, an empty "dummy" 
refrigerant purity test tube that contains no chemicals and which is open 
at both ends. The "dummy" tube may be made of glass, plastic or metal, 
and, in appearance will be substantially identical to the tube 140 shown 
in FIGS. 9 and 10. This tube, preferably, remains in the test fixture at 
all times except when a purity test is being performed, as will be 
described hereinafter. Step 162 indicates the performance of a recovery 
cycle by the recovery and purification system 10 and when that cycle is 
completed as discussed in detail hereinabove, the microprocessor 108 looks 
to its inputs to see if a refrigerant purity test has been selected as 
indicated in step 164. If it has not, the recovery ends as indicated at 
166 and the system shuts down. If a refrigerant purity test has been 
selected the system will shut down to allow installation of a fresh active 
refrigerant purity test tube. Prior to shut down the system will perform a 
purge cycle as indicated by step 168. During the purge cycle, the solenoid 
valves SV6 and SV5 at the entrance and exit, respectively, of the sampling 
tube holder 110 are opened for 15 seconds and refrigerant flows through 
the refrigerant purity test circuit, including the dummy tube, to purge 
the refrigerant purity test circuit piping and fixture of any residual 
moisture or contaminated refrigerant. At the end of the purge cycle the 
microprocessor equalizes the pressure within the system and shuts down as 
shown in step 170. This is a accomplished by shutting off the compressor 
and opening solenoid actuated valves SV1, SV2, and SV4. 
Following equalization all of the solenoid actuated valves SV1 through SV7 
are turned off and the microprocessor controller 108 prompts the operator 
by way of a visual display on the units console 111 showing the word "ADD" 
as indicated at 172. This prompt directs the user to remove the "dummy" 
tube from the sampling tube holder 110 and to install an active 
refrigerant purity test tube into the fixture as indicated at step 174 and 
176. When this is done the operator is instructed to push the units 
"start" button 178 (also on the console). When this is done the unit 10 
restarts and a "Totaltest" refrigerant purity sample is taken. The 
refrigerant purity test 180 actually includes two steps. The first being 
operation of the system in a pre-purity test mode for 30 seconds to assure 
that the refrigerant contained within the units piping and components is 
representative of that contained in the storage cylinder 86. Upon 
initiation of the pre-purity test mode of operation, solenoid valves SV1, 
SV2, and SV4 are all energized to an open position. The solenoid valves 
SV3, SV5/SV6 and SV7 are not energized and are therefore closed. With the 
flow control valves in the condition described the flow of refrigerant 
through the recovery system is similar to that described above in 
connection with the Cylinder Cooling mode with two important exceptions, 
first the solenoid valve SV4 is open and therefore the refrigerant does 
not pass through the expansion device 74. The second important exception 
is that with SV2 open the refrigerant drawn from the storage cylinder via 
conduit 94 will be drawn through the refrigerant sampling conduit 29 and 
into the compressor suction line 40. At this time the refrigerant sampling 
conduit 29 and the purification components 32 and 38 are in parallel fluid 
flow relationship. Because the pressure drop through the purification 
components, is substantially greater, most of the flow will be through 
conduit 29. As a result, under these conditions, the refrigerant 
circulating in the system is of the same purity as the refrigerant 
contained in the storage cylinder 86. 
Following the 15 second pre-purity test mode, the solenoid valves SV5 and 
SV6 are opened and a flow of refrigerant representative of that contained 
within the storage cylinder 86 passes through the refrigerant quality test 
tube. The flow of refrigerant through the refrigerant quality test tube is 
caused by the pressure differential existing between the high and low 
pressure sides of the system which induces the flow of refrigerant through 
conduit 102, solenoid valve SV6, the sampling tube holder 110 (and the 
tube contained therein), solenoid valve SV5 and conduits 106 and 23 to 
thereby return the refrigerant being tested to the suction side of the 
compressor 44. A suitable orifice is provided in conduit 104, to provide 
the necessary pressure drop to assure that the flow of refrigerant through 
the testing tube held in the sampling tube holder 104 is at a rate that 
will assure that the testing tube will receive the proper flow of 
refrigerant therethrough during the TOTALTEST run time in order to assure 
a reliable test of the quality of the refrigerant passing therethrough. 
After a specified period of time, dependent upon the type of refrigerant 
being tested and other variables all of which is programmed into the 
controllers microprocessor, the system then equalizes its pressure and 
shuts down as indicated by step 182 in the same manner as described 
hereinabove with respect to step 170. 
Following this shut down, as indicated in step 184 the user is instructed 
to immediately determine the length of chemical discoloration or staining 
on the refrigerant purity test tube and to ascertain from the materials 
supplied by the test tube manufacturer the refrigerant acid and moisture 
level within the refrigerant. This analysis should be done before removing 
the purity test tube from the fixture. If the analysis of the tube 
indicates that the acid and moisture levels are within acceptable limits 
the recovery and recycle procedure is ended as indicated by step 186. The 
use should the remove the used purity sample tube and reinstall the 
"dummy" tube as indicated at step 187. If the analysis indicates that 
additional recycle time is needed path 188 is followed and the user is 
also instructed to remove the used purity sample tube and reinstall the 
"dummy" tube as indicated at step 190. 
Following installation of the "dummy tube the recovery and purification 
unit 10 is then activated to run for an additional recycle, i.e. 
purification, mode for the desired time. Following this recycle, 192 the 
system returns to the step 164 where the question is again asked whether a 
refrigerant purity test is desired and the system runs through the 
described cycle until the system is shut down either via step 166 or step 
186. At this time all of the refrigerant contained within the cylinder 86 
has been dried and purified to the derived degree and ready for reuse. 
With reference to FIG. 6 the length of time in which the system is run in 
the Recycle mode is determined by the operator as a number of minutes "X" 
which varies as a function of refrigerant type and purity and ambient air 
temperature. The type of refrigerant is known, the ambient temperature may 
be measured, and the purity is determined by the operator upon the 
evaluation of the test tube used in the refrigerant purity test cycle. 
With continued referenced to FIG. 6, upon the end of the selected recycle 
time the system, if so selected by the operator, will run another 
refrigerant purity test, and, if the results of this test so indicate 
another recycle period may be initiated following the procedure set forth 
above. 
The object of the system and control scheme described above is to remove as 
much refrigerant as possible from a system being serviced, under any given 
ambient conditions, or system conditions, while, at all times monitoring 
system control parameters which will assure that the compressor of the 
Recovery system is not subjected to adverse operating conditions. As 
described above, the system control parameter is the pressure ratio P3/P2, 
across the recovery compressor 44. In the example given above a value of 
P3/P2 of 16 was used as the pressure ratio above which the compressor 
could be adversely affected. It should be appreciated that for different 
compressors the value of this parameter could be different. 
The ultimate goal in the control of this system is to limit compressor 
operation to predetermined limits to assure long and reliable compressor 
life. As pointed out above, in the Background of the Invention. the 
internal compressor temperature is considered by compressor experts to be 
the controlling factor in preventing internal compressor damage during 
operation. In the presently disclosed embodiment the pressure ratio has 
been found to be an extremely reliable effective control parameter which 
may be related to the internal compressor temperature and has thus been 
selected as the preferred control parameter in the above described 
preferred embodiment. Pressure differential, (i.e. P.sub.3 -P.sub.2) could 
also be effectively used to control the system. 
It should be appreciated however, that other system control parameters such 
as the compressor discharge temperature as measured by the temperature 
transducer 110 in the compressor discharge line 50, or the compressor 
suction pressure P2 could also be used to control the operation of the 
system, to limit the system to operation only at conditions at which the 
compressor is not adversely effected. 
With respect to temperature, it is generally agreed that an internal 
compressor temperature at which the lubricating oil begins to break down 
is about 325.degree. F. Above this temperature adverse compressor 
operation and damage may be expected. In the present system the controller 
108 has been programmed such that, should the compressor discharge 
temperature, monitored by the temperature transducer 110 exceed a maximum 
of 225.degree. F. regardless of pressure ratio conditions, the system will 
be shut off. 
It is further contemplated that, if the compressor discharge temperature, 
as measured at the transducer 110 were used as the primary system control 
parameter that a temperature in the neighborhood of 200.degree. F. would 
be used to switch the recovery system from a Recover mode to a Cylinder 
Cooling mode of operation in order to assure that the compressor would not 
be adversely affected during operation of the system. 
According to another control method, as mentioned above, the system control 
parameter being sensed for compressor protection could be the compressor 
suction pressure P2. In this case the microprocessor of the controller 108 
would be programmed with compressor suction pressures P2 which would be 
considered indicative of adverse compressor operation, for a range of 
ambient air temperatures and for the different refrigerants which may be 
processed by the system. As an example, when processing refrigerant R-22 
at an ambient air temperature of 90.degree. F. a suction pressure P2 in 
the range of 13 psia to 15 psia would be programmed to change the system 
from a Recover mode Cylinder Cooling mode of operation. 
The outstanding refrigerant recovery capability of a system according to 
the present invention is reflected in the following example. The recovery 
apparatus was connected to a refrigeration system having a system charge 
of 40.0 pounds of refrigerant R-22 at an ambient temperature of 70.degree. 
F. Such a system is typical of a large central air condition system. 
Upon initiation of liquid recovery the system performed the liquid recovery 
sequence for a duration of 15 minutes before shifting to the vapor 
recovery mode of operation. At the point of initiation of vapor recovery 
37.7 pounds had been recovered from the system. Vapor recovery was then 
initiated and ran for 10 minutes during which time an additional 2.1 
pounds of refrigerant was recovered. At this point, the total run time had 
been 25 minutes and a total of 39.8 pounds of refrigerant had been 
recovered from the system. This represents 99.5% of the total charge of 
40.0 pounds, leaving only 0.2 pounds in the system. 
The outstanding refrigerant recovery capability of a system according to 
the present invention is further reflected in the following example of 
vapor recovery only. The recovery apparatus was connected to a 
refrigeration system having a system charge of 4.5 pounds of refrigerant 
R-12 at an ambient temperature of 70.degree. F. Such a system is typical 
of an automobile air conditioning system. 
Upon initiation of recovery the system performed a first Recover cycle for 
8.67 minutes before the system reached the limiting pressure ratio P.sub.2 
/P.sub.3 of 16. At that point 3.73 pounds had been recovered from the 
system. This represents 82.9% of the systems total charge. Typical prior 
art systems would stop at this point, leaving 0.77 pounds, or more than 
17% of the charge in the system. This 0.77 pounds would eventually be 
released to the atmosphere. 
At this point, the system shifted to the Cylinder Cool mode of operation. 
The Cylinder Cool cycle ran for 15 minutes, bringing the cylinder 
temperature (Tstor) down to 10.degree. F. At this point a second Recover 
cycle was initiated by the system controller. The second Recover cycle ran 
for 3.8 minutes at which time Recover was terminated when the suction 
pressure P2 fell to 4.0 psia. 
At this point, the total system run time had been 27.5 minutes and a total 
of 4.42 pounds of refrigerant had been recovered from the system. This 
represents 98.2% of the total charge of 4.5 pounds, leaving only 0.08 
pounds in the system. 
Following completion of recovery and purification, the storage cylinder 86 
contains clean refrigerant which may be returned to the refrigeration 
system. With reference to FIG. 4, the Recharge mode, when selected, 
results in simultaneous opening of valves SV1 and SV3 to establish a 
direct refrigerant path from the storage cylinder 86 to the refrigeration 
system 12. All other valves and the compressor and condenser are 
de-energized in this mode. The amount of refrigerant to be delivered to 
the system is selected by the operator, and, the controller 108, with 
input from the liquid level sensor 92 will assure accurate recharge of the 
selected quantity of refrigerant to the system. 
This invention may be practiced or embodied in still other ways without 
departing from the spirit or central character thereof. The preferred 
embodiments described herein are therefore illustrative and not 
restricted. The scope of the invention being indicated by the appended 
claims and all variations which come within the meaning of the claims are 
intended to be embraced therein.