Abstract:
An apparatus for recovering and recycling refrigerant is provided. The apparatus includes a separation unit, a compressor, and a receiver tank. The separation unit is provided for condensing compressed refrigerant and for vaporizing contaminated refrigerant. The separation unit includes a multichamber structure having a high pressure region and a low pressure region. The high pressure region includes a high pressure inlet for providing compressed refrigerant vapor to the high pressure region, a high pressure outlet for removing condensed refrigerant from the high pressure region, and a compressor oil outlet for removing compressor oil from the high pressure region. The low pressure region includes a low pressure inlet for introducing contaminated refrigerant into the low pressure region, a low pressure outlet for removing vaporized refrigerant from the low pressure region, and a refrigerant oil outlet for removing refrigerant oil from the low pressure region. The compressor is provided for compressing refrigerant from the low pressure outlet of the separation unit to provide compressed refrigerant for feeding to the high pressure inlet of the separation unit. The receiver tank is provided for receiving condensed refrigerant from the high pressure outlet of the separation unit. A method for recovering and recycling refrigerant is provided.

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus and method for recovering and recycling refrigerant from an air conditioning unit. 
     BACKGROUND OF THE INVENTION 
     Most modem air conditioning equipment employ one of several organic solvent compositions, commonly referred to as chlorofluorocarbon compounds (CFCs), as a working fluid (refrigerant). For various reasons, such as wearing of the seals in the air conditioning equipment&#39;s compressor, the refrigerant in the equipment may eventually become contaminated with dirt, oil and/or moisture. These contaminants affect the efficiency of the equipment and may eventually lead to damage of the compressor and other components in the equipment. Thus, it is desirable to replace the refrigerant periodically to avoid damaging the equipment and to restore the equipment&#39;s overall efficiency. Also, in the event of a failure of the equipment, it is typically required that the refrigerant be removed from the equipment prior to servicing. 
     Previously, the most common method of removing the refrigerant from the equipment was to vent the refrigerant into the atmosphere and to replace it with virgin refrigerant as required. However, problems exist with this method of removing the refrigerant. The release of CFC compounds into the atmosphere results in the depletion of the ozone layer therein. As the ozone layer is the principal filter in the atmosphere for removing the sun&#39;s ultraviolet radiation, much concern has been expressed about its depletion as it is expected to lead to many problems. For example, it is expected that an upturn in related health problems such as skin cancer will occur. Accordingly, many governments are passing legislation restricting or prohibiting the use of and/or releases of CFC compounds into the atmosphere. These restrictions pose a serious problem to refrigeration equipment manufacturers and servicers who no longer can release CFC-type refrigerants into the atmosphere. Furthermore, replacing refrigerant which has been vented to the atmosphere is expensive and may be difficult to obtain. 
     Refrigerant recovery and recycling systems are described in, for example, U.S. Pat. Nos. 3,699,781; 4,285,206; 4,364,236; 4,805,416; 4,768,347; 4,809,520; 5,072,593; 5,245,840; 5,335,512; 4,809,520; 5,353,603; 5,617,731; and 5,934,091. 
     SUMMARY OF THE INVENTION 
     An apparatus for recovering and recycling refrigerant is provided. The apparatus includes a separation unit, a compressor, and a receiver tank. The separation unit is provided for condensing compressed refrigerant and for vaporizing contaminated refrigerant. The separation unit includes a multichamber structure having a high pressure region and a low pressure region. The high pressure region includes a high pressure inlet for providing compressed refrigerant vapor to the high pressure region, a high pressure outlet for removing condensed refrigerant from the high pressure region, and a compressor oil outlet for removing compressor oil from the high pressure region. The low pressure region includes a low pressure inlet for introducing contaminated refrigerant into the low pressure region, a low pressure outlet for removing vaporized refrigerant from the low pressure region, and a refrigerant oil outlet for removing refrigerant oil from the low pressure region. The compressor is provided for compressing refrigerant from the low pressure outlet of the separation unit to provide compressed refrigerant for feeding to the high pressure inlet of the separation unit. The receiver tank is provided for receiving condensed refrigerant from the high pressure outlet of the separation unit. 
     The apparatus preferably includes a manifold assembly. The manifold assembly is provided for controlling the flow of processing fluid through the apparatus. The manifold assembly includes several passageways for directing the flow of processing fluid. For example, the manifold assembly preferably includes two or more of the following lines: a contaminated refrigerant recovery line; a vaporized refrigerant line; a compressed refrigerant line; and a condensed refrigerant line. The contaminated refrigerant recovery line is provided for directing contaminated refrigerant into the low pressure region of the separation unit. The vaporized refrigerant line is provided for directing vaporized refrigerant from the low pressure region of the separation unit to the compressor. The compressed refrigerant line is provided for directing compressed refrigerant into the high pressure region of the separation unit. The condensed refrigerant line is provided for directing condensed refrigerant from the high pressure region of the separation unit to the receiver tank. Valves can be provided on each of these lines for directing flow through the lines. The valves are preferably solenoid valves and are preferably controlled by a microprocessor. 
     The apparatus for recovering and recycling refrigerant can include a filter for filtering the contaminated refrigerant prior to introduction into the separation unit. The filter preferably includes a magnet for attracting metallic particulates. In addition, the filter preferably includes a screen for obstructing the flow of particular sized particulates or fibers into the separation unit. Preferably, the filter including a magnet is provided upstream of any solenoid valves. 
     A method for recovering and recycling refrigerant is provided by the invention. The method can be implemented using the apparatus of the invention. The method can include steps of feeding contaminated refrigerant to the separation unit; compressing the vaporized refrigerant from the low pressure outlet of the separation unit to provide compressed refrigerant vapor; feeding the compressed refrigerant vapor to the high pressure inlet of the high pressure region of the separation unit; separating oil from the compressed refrigerant and recovering the oil in the separation unit; condensing the compressed refrigerant vapor to provide condensed refrigerant in the separation unit; and feeding the condensed refrigerant to the receiver tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described by way of example only, with reference to the attached figures wherein: 
     FIG. 1 is a portable apparatus for recovering and recycling refrigerant according to the principles of the invention; 
     FIG. 2 is a schematic representation of the apparatus for recovering and recycling refrigerant from an air conditioning unit of FIG. 1; 
     FIG. 3 is a schematic representation of a partial, alternative embodiment of an apparatus and method for recovering and recycling refrigerant according to the principles of the invention; 
     FIG. 4 is a perspective, cut away view of the separation unit of the apparatus for recovering and recycling refrigerant according to the principles of the invention; 
     FIG. 5 is a perspective view of the combination separation unit and manifold assembly according to the principles of the invention; 
     FIG. 6 is a side view of a trap according to the principles of the invention; 
     FIG. 7 is a sectional view of the trap of FIG. 6 taken along lines  6 — 6 ; 
     FIG. 8 is a plan view of the control panel of a dual refrigerant recovery and recycling apparatus according to the principles of the invention; and 
     FIGS. 9 ( a )-( c ) shows a process flow diagram depicting a preferred operation of a portable apparatus for recovering and recycling refrigerant according to the principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now referring to FIGS. 1 and 2, a portable apparatus for recovering and recycling refrigerant according to the invention is provided at reference  10 . The apparatus  10  can be referred to as a single pass apparatus because the refrigerant passes through the system essentially once for purification, rather than being processed in a loop. The apparatus  10  includes a housing  12  on a wheeled cart  14 . Additionally included is a handle  16  for allowing one to push the apparatus  10  on wheels  18 . A control panel  20  is provided for operating the apparatus. A microprocessor  21  is provided for controlling the operation of the apparatus. A gas analyzer  23  can be provided. 
     The components of the apparatus  10  through which refrigerant flows include a filter  22 , a compressor  24 , a separation unit  26 , a manifold assembly  28 , a low pressure hose  30 , a low pressure hose fitting  32 , a high pressure hose  34 , a high pressure hose fitting  36 , and a receiver tank or refrigerant storage tank  38 . Additionally included is a fan  37  for directing air across the separation unit  26 , a vacuum pump  27 , and a scale  29  for weighing the storage tank  38 . It should be appreciated that the various components are in fluid connectivity via tubing or conduits which are not shown in FIG. 1 but are depicted in FIG.  2 . 
     The apparatus for recovering and recycling refrigerant  10  is capable of performing several operations. A first operation includes the recovery of refrigerant from an air conditioning unit. In general, this involves the recycling of the used refrigerant found in an air conditioning unit (such as an automobile air conditioning unit) or a refrigeration unit (such as a refrigerator or freezer) to provide a purified refrigerant which can be introduced into an air conditioning unit or a refrigeration unit as new or recycled refrigerant. Another operation includes the evacuation of an air conditioning unit or a refrigeration unit in order to dry out its lines. Another operation includes the charging of purified refrigerant into an air conditioning unit or a refrigeration unit. 
     Now with reference to FIG. 2, the recovery and recycling of contaminated refrigerant from an air conditioning unit is discussed in detail. The following description generally follows the operation of the apparatus  10  for processing contaminated refrigerant recovered from an automobile air conditioning unit to provide a purified refrigerant, evacuating the air conditioning unit, and then charging purified refrigerant into the air conditioning unit. It should be understood that the phrase “contaminated refrigerant” refers to the refrigerant recovered from an air conditioning unit or refrigeration unit. The phrase “contaminated refrigerant” does not require a particular degree of contamination. The contaminated refrigerant may be relatively old or new, and may contain varying amounts of impurities which can be separated from the refrigerant to provide a purified refrigerant for charging into an air conditioning unit or refrigeration unit. The contaminated refrigerant is likely to include particulates, oil, water, and air which should be removed to a desired extent to provide purified refrigerant which can then be introduced back into an automobile air conditioning system. In the context of the following description, the refrigerant can be referred to as the processing fluid. Although the following description is in the context of recycling refrigerant from an automobile air conditioning unit, it can be applied to other types of air conditioning units and to refrigeration units. 
     The phrases “high pressure” and “low pressure” are used to describe the general condition of the processing fluid. For example, high pressure processing fluid can generally be found downstream of a compressor. In contrast, low pressure processing fluid can generally be found upstream of a compressor. The phrases high pressure processing fluid and low pressure processing fluid should not be construed as to require a particular pressure value. 
     The low pressure hose  30  is connected to the low pressure side of an automobile air conditioning unit via the low pressure hose fitting  32 . The high pressure side hose  34  is connected to the high pressure side of an automobile air conditioning unit via the high pressure hose fitting  36 . The hose fittings  32  and  36  include valves  33  which, once attached to the appropriate port on the automobile air conditioning system, can be opened to provide flow therethrough. The low pressure hose  30  and the high pressure hose  34  connect to the manifold assembly  28 . Much of the flow through the apparatus  10  is directed by the flow through the manifold assembly  28 . Much of the schematic shown in FIG. 2 is a representation of the flow through the manifold assembly  28 . The double arrows  39  indicate the exterior surface  29  of the manifold assembly  28 . Accordingly, FIG. 2 schematically illustrates the flow within the manifold assembly  28  as corresponding to the lines or conduits within the double arrows  39 . An advantage of the manifold assembly  28  is that it provides a reduction in the amount of tubing, such as copper tubing, from the amount used in many prior refrigerant recycling apparatuses. The passageways and interconnected passageways within the manifold assembly  28  direct the flow of refrigerant. 
     Contaminated refrigerant  45  flows from the low pressure side hose  32  through the low pressure conduit  40  and from the high pressure side hose  34  through the high pressure conduit  42 . As contaminated refrigerant flows into the apparatus  10 , the low pressure conduit valve  44  and the high pressure conduit valve  46  are open. Contaminated refrigerant then flows through conduits  48  and  50 , through recovery check valve  52 , through recovery valve  54  which is open, through the contaminated refrigerant inlet line  55  and into the separation unit  26 . The recovery check valve  52  provides one-way flow of contaminated refrigerant into the separation unit  26 . 
     The separation unit  26  functions as a combination heat exchanger/evaporator/condenser and oil separator. The separation unit  26  includes multiple chambers. See FIG.  4 . The separation unit  26  is arranged to provide a bottom region  57  and a top region  58 . Liquid (i.e., condensates) tends to collect in the bottom region  57 , and gas (i.e., volatiles) tends to collect in the top region  58 . The contaminated refrigerant is introduced into a first evaporation chamber  60  which is in communication with a second evaporation chamber  62 . The first evaporation chamber  60  is in communication with the second evaporation chamber  62  via a first evaporator conduit  64  and a second evaporator conduit  66 . The first evaporator conduit  64  is provided in the bottom region  56  of the separation unit  26  and is provided to allow flow of oil between the two evaporation chambers  60  and  62 . The second evaporator conduit  66  is provided in the top region  58  for providing flow of gas between the evaporator chambers  60  and  62 . It is generally not desirable for gaseous refrigerant to bubble or percolate through oil  65  puddled at the bottom of the separation unit  26 . Accordingly, the second evaporator conduit  66  allows volatilized refrigerant to flow directly into the second evaporation chamber  62 . 
     As contaminated refrigerant flows into the first evaporation chamber  60 , the refrigerant may be entirely liquid, entirely gaseous, or a mixture of liquid and gas. Heat transfers to the contaminated refrigerant causing vaporization of the refrigerant. Oil and other nonvolatiles collect in the bottom region  57  of the first and second evaporation chambers  60  and  62 . The first evaporator conduit  64  provides for fluid communication of liquid (i.e., nonvolatiles and liquid refrigerant) between the first and second evaporation chamber  60  and  62 . Vaporous refrigerant generally flows through the second evaporator conduit  66  and into the second evaporator chamber  62 . If nonvolatiles are not clogging the first evaporator conduit  64 , the vaporous refrigerant can flow through the first evaporator conduit  64  and into the second evaporation chamber  62 . In an alternative embodiment of the invention, it is possible to provide only one evaporation chamber. That is, the separation unit can be provided with a single evaporation chamber which provides for the volatilization of refrigerant and the separation of refrigerant from nonvolatiles. 
     The reference to “volatilized” components refers to the components leaving the separation unit  26  in a gaseous state. There is no requirement that the volatilized components are volatilized within the separation unit. It is possible that part of the volatilized components is gaseous prior to introduction into the separation unit  26 . The volatilized components generally include refrigerant, moisture and air. It should be understood that if moisture and/or air are not present in the contaminated refrigerant, it is expected that they would not be present in the volatilized components. The volatilized components  70  exit the second evaporator chamber  62  via volatilized components line  72 . 
     The volatilized components flow through the filter  22 . The filter is preferably a desiccant filter  74  which removes water from the refrigerant. A commercially available desiccant filter which can be used in the invention is available from Alco, Inc. A site glass  75  can be provided for determining when it is appropriate to replace the desiccant filter. If the water concentration in the purified refrigerant is too high, the desiccant filter should be replaced. It is expected that the desiccant filter will be replaced after about 30 hours of operation or after having serviced about 150 automobile air conditioning units. Preferably, the site glass  75  includes a moisture indicator  76  which shows a green color when the purified refrigerant is sufficiently moisture free. When the moisture indicator  76  turns yellow, the water concentration in the purified refrigerant is too high, and the desiccant filter should be replaced. 
     The refrigerant leaves the filter  74  via line  78  and passes through the compressor  24 . After leaving the filter  74 , the refrigerant can be referred to as purified refrigerant. A commercially available compressor which can be used in this invention is a ⅓ HP compressor. In general, it is expected that the compressor  24  will compress a purified refrigerant  80  to a pressure of at least about 100 psi. While passing through the compressor  24 , the purified refrigerant  80  tends to pick up small amounts of oil from the compressor. In order to maintain proper functioning of the compressor  24 , it is desirable to remove the oil from the refrigerant and return it to the compressor. The concept of returning oil to a compressor is not new and commercially available oil separators have been sold for this purpose for several years. An exemplary company that provides compressor oil separators is Temprite, Inc. The applicants discovered that the oil can be removed from the purified refrigerant  80  in the separation unit  26 . That is, a separate compressor oil separator is not required by the invention, and is preferably not included as part of the apparatus  10 , although it can be included. 
     The purified refrigerant  80  leaves the compressor  24  via high pressure line  82  and is introduced into the first high pressure chamber  86 . Gaseous purified refrigerant flows via the high pressure conduit  88  into the second high pressure chamber  90 . The purified refrigerant is generally provided at a fairly high temperature as a result of the action of the compressor  24 . Accordingly, heat flows from the purified refrigerant to the contaminated refrigerant provided within the separation unit  26 . In view of this heat transfer, it is expected that the compressor oil  89  will condense at the bottom region  57  of the first high pressure chamber  86 . It is expected that the purified refrigerant that condenses in the bottom region  57  of the second high pressure chamber  90  will be essentially free of oil. 
     The condensed purified refrigerant  91  provided at the bottom of the second high pressure chamber  90  is removed from the separation unit  26  via the condensed refrigerant outlet line  92  and through the check valve  94 . The condensed refrigerant then flows through line  96  and through the moisture indicator  75 . The purified refrigerant then flows through line  102 , through the open tank valve  104 , through the tank refrigerant line  106  and into the refrigerant storage tank  38  where the condensed, purified refrigerant is stored. A scale  29  is provided for measuring the mass of refrigerant within the tank  38 . By measuring the mass, temperature and pressure within the tank  108 , the amount of air provided in the tank  38  can be calculated and bled out through the air bleed line  112  and the air outlet valve  114 . 
     During the recovery operation, the low pressure conduit valve  44 , the high pressure conduit valve  46 , the recovery valve  54 , and the tank valve  104  are open. The oil injection valve  120 , the evacuation valve  122 , the charge valve  124 , the compressor oil return valve  123 , the oil drain valve  126 , and the air outlet valve  114  are closed. 
     The low pressure gauge  130  and the high pressure gauge  132  are provided for observing the pressure within the low pressure conduit  40  and the high pressure conduit  42 , respectively. Pressure switches  134  and  136  are provided for detecting low pressure and high pressure conditions in the low pressure conduit  40  and the high pressure conduit  42 , respectively. A refrigerant tank gauge  138  is provided for observing the pressure within the refrigerant storage tank  38 . A pressure switch  139  is provided for detecting pressure conditions in the refrigerant storage tank  38 . Once the pressure switch  134  detects a predetermined low pressure in the low pressure conduit  40 , a signal is provided to a microprocessor and the recovery valve  54  closes and the compressor  24  turns off. The evacuate valve  122  then opens and the vacuum pump  27  turns on to further evacuate and dry out the air conditioning unit. Typically, the vacuum pump  27  is vented to the atmosphere via atmospheric vent line  142 . After running for a period of time, the evacuate valve  122  closes and the vacuum pump  27  turns off. 
     Once the pressure inside the automobile air conditioning unit decreases to a predetermined level, such as eight inches of mercury, it is expected that almost all of the refrigerant has been evacuated and small amounts of air and moisture remain in the automobile air conditioning unit. Thus, the vacuum pump  27  vents to the atmosphere. Once the vacuum pump  27  has run for a predetermined length of time, such as between 5 and 60 minutes, it is believed that the automobile air conditioning unit is ready to be charged with purified refrigerant. Preferably, the vacuum pump  27  is at least a 1.5 cfm pump, and more preferably a 7 cfm pump. 
     While the compressor  24  and the separation unit  26  are pressurized, the oil return valve  120  and the oil drain valve  126  are opened to allow oil to drain from the separation unit  26 . That is, compressor oil  89  flows through the compressor oil outlet line  150 , through the compressor oil return valve  123 , through the oil return line  152  and into the compressor  24 . The refrigerant oil  65  flows through the refrigerant oil recovery line  162 , through the oil drain valve  126 , and into the oil drain  164 . The opening of the compressor oil return valve  123  additionally helps balance the pressure across the compressor  24  which is believed to assist in start up. Once the oil has been removed from the separation unit  26 , the valves  126  and  123  are closed. It is expected that the compressor oil  89  may contain condensed refrigerant. It is expected that the refrigerant will vaporize in the compressor  24  and then circulate back into the separation unit  26 . 
     The amount of oil provided in the oil drain  164  is preferably measured. This allows one to determine how much oil needs to be reintroduced into the air conditioning unit. In general, it is expect that the quantity of oil recovered from an air conditioning unit should be replaced. The observation of the amount of oil recovered can be a visual observation of a volume of oil. The corresponding volume of fresh oil  166  can then be injected through the oil injection valve  120  via oil inlet line  168 , oil inlet check valve  170 , and oil inlet line  172 . It is expected that the fresh oil  166  will flow into the air conditioning unit because of the low pressure condition created by the vacuum pump  27 . If all of the oil does not flow into the air conditioning unit, it is expected that the subsequent charge of refrigerant into the air conditioning unit will help introduce the oil into the air conditioning unit. 
     After refrigerant has been recovered from an air conditioning unit and the air conditioning unit has been evacuated, refrigerant can be introduced into the air conditioning unit. The tank valve  104 , the charge valve  124 , the low pressure conduit valve  44 , and the high pressure conduit valve  46  are open while a predetermined amount of refrigerant is introduced into the air conditioning system. After the predetermined amount of refrigerant leaves the refrigerant tank  38 , the valves close and the fittings  32  and  36  can be removed from the air conditioning unit. The charge to the automobile air conditioning unit is determined based upon the unit specification. Based upon the information provided by the weight scale  29 , the microprocessor  21  determines the length of time the refrigerant tank valve  104  remains open in order to provide the desired charge to the automobile air conditioning unit. 
     Referring to separation unit  26 , it is pointed out that there are several tubes of varying lengths which extend into the several chambers. A refrigerant oil recovery tube  200  is provided extending into the bottom region  57  in order to recover condensed compressor refrigerant oil  65 . A contaminated refrigerant tube  201  is provided extending into the upper region  58 . A condensed refrigerant recovery tube  202  is provided extending into the bottom region  57  for recovery of condensed refrigerant. A compressor oil recovery tube  203  is provided extending into the lower region  57  for recovery of condensed compressor oil  89 . A compressed refrigerant tube  204  is provided for introducing compressed refrigerant into the upper region  58 . In general, the tube  204  extends sufficiently far down to avoid the likelihood of compressor oil flowing into the second high pressure chamber  90 . 
     Now referring to FIGS. 4 and 5, the separation unit  26  and the combination of the separation unit  26  and the manifold assembly  28  are shown in detail. The separation unit  26  includes first and second low pressure chambers  60  and  62  and first and second high pressure chambers  86  and  90 . It is an advantage of the invention that the separation unit  26  can be formed by extruding metal, such as, aluminum. In general, the metal is preferably one which provides for good heat transfer. By providing several chambers, the applicants were able to avoid the use of coils which are often found in prior refrigerant recovery apparatuses. The separation unit  26  can include a bottom plate or cover  180 . The manifold assembly  28  can function as the top or cover  182 . In addition, bolts  184  can be provided extending through the top  182 , the extrusion  184 , and the bottom cover  180 . The extrusion  184  preferably includes holes  186  through which the bolts  185  extend. Accordingly, the manifold assembly  28  and the separation unit  26  can be held tightly together. 
     The manifold assembly  28  preferably includes interconnecting passageways  190  which are schematically depicted by FIG.  2 . The valves  44 ,  122 ,  46 ,  124 ,  54  and  123  are preferably solenoid valves and are depicted in FIG. 5 by reference numeral  192 . 
     Now referring to FIG. 3, an alternative embodiment of an apparatus and method for recovering and recycling refrigerant is provided at reference numeral  210 . The apparatus  210  includes fresh oil  212  which can be injected through the oil injection valve  214  via oil inlet line  216 , oil inlet check valve  218 , and oil inlet line  220 . The oil then flows into the refrigerant recovery and delivery line  222  which can be either the high pressure line or the low pressure line. A valve  224  is provided to control flow through the line  222 . A pressure gauge  226  is provided for observing the pressure in the line  222  and a pressure switch  228  is provided for detecting pressure conditions within the line  222 . In addition, a hose  230  and a fitting  232  are provided for attaching to an air conditioning unit or a refrigeration unit. The remainder of the apparatus can be configured similar to that shown in FIG. 2 
     It should be appreciated that while the recovery of contaminated refrigerant and the charging of purified refrigerant is described in the context of using both a high pressure connection and a low pressure connection to an air conditioning unit or a refrigeration unit, it should be understood that the invention can be practiced using a single line for recovery and/or charging. 
     The apparatus  10  preferably includes filters  240  for obstructing the flow of certain sized particulate and/or fibrous materials into the apparatus. Preferably, the filters  240  are provided between the low pressure hose  30  and the manifold assembly  28  and between the high pressure hose  34  and the manifold assembly  28 . A filter  240  can additionally be provided between the purified refrigerant line  102  and the manifold assembly  28 . The filters  240  can be provided with screens  242  which provide the filtering. A preferred embodiment of the filters  240  are depicted in FIGS. 6 and 7 at reference numeral  250 . The filter  250  can be referred to as a magnet and screen filter. The magnet and screen filter  250  includes an inlet  242 , a screen  244 , a magnet  246  and an outlet  248 . As refrigerant flows from the inlet  242  to the outlet  248 , metallic particulates become magnetically attached to the magnet  246 . Non-metallic particulates or fibers can be caught by the screen  244 . As shown, the screen is preferably provided as a cylindrical screen  260 , and the magnet  246  is preferably attached to the filter housing  262  by adhesive  264  which can be an epoxy adhesive. The portion of the filter housing  262  to which the magnet  246  is attached is preferably a plug  256  which can be removed so as to clean the filter. As shown, the plug  256  includes threads  255  for screwing into the housing  262 . A gasket  257  can be provided. Preferably, the plug  256  can be unscrewed from its location and then replaced by screwing back into its location. The screen  244  can be attached to the plug  256 . 
     The magnet and screen filter  250  is advantageous because it provides for trapping of metallic particles which may otherwise become attached to the solenoid valves and result in clogging of the solenoid valves. The magnet and screen filters are preferably provided outside of the manifold assembly and attached to the hoses which are used to service the air conditioning units or refrigeration units. 
     Now referring to FIG. 8, an alternative embodiment of the apparatus for recovering and recycling refrigerant is indicated at reference numeral  300 . The apparatus can be referred to as a dual refrigerant recovery and recycling apparatus because it is capable of handling two different types of refrigerant. The operation of the apparatus is similar to the operation of the apparatus described in FIG.  2 . In general, two separate apparatuses are combined together. One apparatus can be used for the recovery of R-134a refrigerant and the other apparatus can be used for the recovery of R-12 refrigerant. The vacuum pump  27  can be provided as a shared piece of equipment between the two apparatuses. A prior dual refrigerant recovery apparatus is described in U.S. Pat. No. 5,934,091 to Hanson, et al., the entire disclosure of which is incorporated herein by reference. 
     As shown in FIG. 8, a low pressure gauge  302 , a high pressure gauge  304 , and a tank pressure gauge  306  are provided for observing the pressure in the apparatus for recovering one type of refrigerant. Furthermore, a low pressure gauge  308 , a high pressure gauge  310 , and a tank pressure gauge  312  are provided for observing the pressure conditions in the apparatus for recovering a different type of refrigerant. In addition, a power switch  314  is provided for turning on the apparatus, a high pressure warning lights  316  are provided for identifying when pressure conditions reach a potentially dangerous state, air purge buttons  318  are provided for venting air from the refrigerant tanks, a switch  319  is provided for selecting which refrigerant to recover, and an operation panel  320  is provided for operating the apparatus. 
     Now referring to FIGS. 9 ( a )-( c ), a process flow diagram is provided depicting an exemplary operation of an apparatus for recovering and recycling refrigerant according to the invention. 
     While the invention has been described in the context of recovering and recycling refrigerant from an automobile air conditioning unit, it should be understood that the principles of the invention, including the apparatus and method, can be applied to recovering and purifying refrigerant from other sources including refrigerators, freezers, and home and commercial air conditioning systems. In addition, it should be understood that the invention can be practiced for processing refrigerants including R-12, R-134A and other available refrigerants. 
     The above specification provides a complete description of the manufacture and use of the apparatus of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.