Abstract:
A refrigerant service system comprises a compressor having a compressor inlet and a compressor outlet, an inlet conduit, an outlet conduit, and an accumulator including an outer housing shell and an inner housing shell disposed within the outer housing shell. A first chamber is defined in the accumulator between the inner housing shell and the outer housing shell, the first chamber being configured to receive refrigerant from the inlet conduit and discharge the refrigerant to the compressor inlet. A second chamber is defined in the accumulator within the inner housing shell, the second chamber being configured to receive the refrigerant from the compressor outlet and discharge the refrigerant to the outlet conduit. Heat is transferred from the refrigerant in the second chamber through the inner shell to the refrigerant in the first chamber.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit of priority to co-pending U.S. provisional application No. 61/911,643, entitled “Heat Exchanger for a Refrigerant Service system,” which was filed on Dec. 4, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to refrigeration systems, and more particularly to refrigerant recovery systems for refrigeration systems. 
       BACKGROUND 
       [0003]    Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles including, for example, automobiles. Over time, the refrigerant included in these systems gets depleted and/or contaminated. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant included therein may be periodically replaced or recharged. 
         [0004]    Portable carts, also known as recover, recycle, recharge (“RRR”) refrigerant service carts or air conditioning service (“ACS”) units, are used in connection with servicing refrigeration circuits, such as the air conditioning unit of a vehicle. The portable machines include hoses coupled to the refrigeration circuit to be serviced. A vacuum pump and compressor operate to recover refrigerant from the vehicle&#39;s air conditioning unit, flush the refrigerant, and subsequently recharge the system from a supply of either recovered refrigerant and/or new refrigerant from a refrigerant tank. 
         [0005]    Refrigerant vapor entering the ACS unit first passes through a system oil separator or accumulator to remove oil entrained in the refrigerant from the air conditioning system. Next, the refrigerant passes through a filter and dryer unit to remove contaminants and moisture from the recovered refrigerant and then the refrigerant is pressurized by a compressor. 
         [0006]    Refrigerant vapor is very hot as it exits the compressor during an AC recovery cycle. In a typical flow path, this hot refrigerant enters a compressor oil separator, which separates any compressor oil entrained in the refrigerant from the compressor pass-through from the refrigerant vapor. The compressor oil is then returned to the compressor, and the refrigerant vapor continues along the flow path into a heat exchanger, which assists within the system oil separator or accumulator found earlier in the path. The compressor oil separator and system heat exchanger are two completely different entities within the standard flow path. 
         [0007]    In current ACS units, the accumulator, finned-tube heat exchanger, filter and dryer unit, and compressor oil separator are all mounted to the same aluminum manifold block. This enables efficient routing between the components within the block. This also allows for easy access to specific areas within the flow path for valves and sensory components, such as pressure transducers or high pressure switches. 
         [0008]    In present systems, a relatively large manifold block footprint is necessary to physically accommodate the components, particularly the larger components such as the heat exchanger, filter and dryer unit, and compressor oil separator. Additionally, heat is lost by the refrigerant in the compressor oil separator and flow tubes between the compressor, compressor oil separator, and heat exchanger, limiting the amount of heat transferred to the accumulator and reducing the overall efficiency of the recovery unit. What is needed, therefore, is an improved heat exchanger for a refrigerant recovery unit. 
       SUMMARY 
       [0009]    A refrigerant service system according to the disclosure comprises a compressor having a compressor inlet and a compressor outlet, an inlet conduit, an outlet conduit, and an accumulator including an outer housing shell and an inner housing shell disposed within the outer housing shell. A first chamber is defined in the accumulator between the inner housing shell and the outer housing shell, the first chamber being configured to receive refrigerant from the inlet conduit and discharge the refrigerant to the compressor inlet. A second chamber is defined in the accumulator separate from the first chamber within the inner housing shell, the second chamber being configured to receive the refrigerant from the compressor outlet and discharge the refrigerant to the outlet conduit. The first and second chambers are arranged such that heat is transferred from the refrigerant in the second chamber through the inner shell to the refrigerant in the first chamber. The refrigerant service system according to the disclosure has the advantage that the accumulator includes two chambers, such that compressor oil separation and system oil separation are performed in the same accumulator, requiring less installation space. Furthermore, heat from the refrigerant in the second chamber is used to heat the refrigerant in the first chamber, reducing energy losses in the refrigeration service system and power consumption of the system. 
         [0010]    In another embodiment, the refrigerant service system further includes a compressor oil return line connecting the compressor oil outlet passage to an oil return port of the compressor and configured to return compressor oil removed from the refrigerant in the second chamber to the compressor. Compressor oil collected in the second chamber can advantageously be returned to the compressor. 
         [0011]    In yet another embodiment, a compressor oil outlet passage is defined in the inner shell having a first end that opens to the second chamber and a second end that connects to the compressor oil return line. Compressor oil collected in the second chamber can advantageously be returned through the compressor oil outlet passage defined in the inner shell through the compressor oil return line to the compressor. 
         [0012]    In a further embodiment according to the disclosure, the accumulator includes a compressor oil suction tube having a first end connected to the compressor oil return line and a second end positioned at a bottom region of the second chamber. Compressor oil collected in the second chamber can advantageously be returned through the compressor oil suction tube in the second chamber and the compressor oil return line to the compressor. 
         [0013]    In another embodiment, a bottom end of the outer shell is tapered to a lowest region, and the lowest region includes a system oil drain. System oil collected in the first chamber can therefore be drained from the lowest region of the first chamber. 
         [0014]    In one embodiment, the accumulator further comprises a refrigerant inlet port connected to the inlet conduit and an input injection tube having a first end connected to the refrigerant inlet port and a second end configured to discharge refrigerant against an outer surface of the inner shell. Refrigerant can advantageously be discharged against the outer surface of the heated inner shell, facilitating vaporization of the refrigerant. 
         [0015]    In another embodiment an outer surface of the inner shell includes a plurality of ribs along an axial length of the outer surface. The ribs increase the surface area of the outer surface and facilitate better heat transfer. 
         [0016]    In a further embodiment, an outer surface of the inner shell is cylindrical and smooth to enable liquid oil on the outer surface to flow downwardly and drip from the inner shell. 
         [0017]    In yet a further embodiment, the refrigerant service system includes a manifold block to which the inner and outer shells are mounted. The manifold block defining the inlet conduit, a first conduit through which the refrigerant flows between the first chamber and the compressor inlet, a second conduit through which the refrigerant flows between the compressor outlet and the second chamber, and the outlet conduit. The manifold block is easily manufactured to tight tolerances and enables precise routing of the conduits in the refrigerant service system. The manifold block further serves as a firm support for the inner and outer shells of the accumulator. 
         [0018]    The accumulator may include a coalescing filter located at an inlet of the second chamber and configured to coalesce compressor oil condensed from the refrigerant in the second chamber. The coalescing filter improves separation of the compressor oil from the refrigerant in the second chamber. 
         [0019]    In another embodiment, the refrigerant service system further comprises a filter and dryer unit positioned between the first chamber and the compressor inlet and configured to receive refrigerant from the first chamber and discharge the refrigerant to the compressor inlet. The filter and dryer unit advantageously removes moisture and particles from the refrigerant before it arrives at the compressor. 
         [0020]    In one embodiment, the refrigerant service system includes a refrigerant storage vessel configured to receive the refrigerant from the outlet conduit. The refrigerant storage vessel enables the recovered refrigerant to be stored for subsequent reuse. 
         [0021]    In yet another embodiment according to the disclosure, a method of recovering refrigerant from an air conditioning system comprises moving refrigerant from a first chamber defined between an outer shell and an inner shell of a heat exchanger to a compressor, and heating and compressing the refrigerant with the compressor after the refrigerant leaves the first chamber of the heat exchanger. The method further includes moving the heated and compressed refrigerant from the compressor to the second chamber and transferring heat from the refrigerant in the second chamber through the outer shell to the refrigerant in the first chamber to vaporize the refrigerant in the first chamber and separate system oil from the refrigerant in the first chamber and to condense compressor oil from the refrigerant in the second chamber. The method facilitates compressor oil separation and system oil separation in the same accumulator, enabling a more compact unit to perform the method. Furthermore, heat from the refrigerant in the second chamber is used to heat the refrigerant in the first chamber, reducing energy losses and power consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic diagram of a refrigerant service system. 
           [0023]      FIG. 2  is a side perspective view of the manifold of the refrigerant service system of  FIG. 1 . 
           [0024]      FIG. 3  is a cutaway side perspective view of the manifold of  FIG. 2  showing the combined heat exchanger and compressor oil separator within the accumulator. 
           [0025]      FIG. 4  is a cross-sectional view of the accumulator of  FIG. 3  having the combination heat exchanger and compressor oil separator located within the accumulator. 
           [0026]      FIG. 5  is a bottom view of the manifold block of the refrigerant service system of  FIG. 4 . 
           [0027]      FIG. 6  is a side view of the combined heat exchanger and compressor oil separator of  FIG. 4 . 
           [0028]      FIG. 7  is a cutaway view of a manifold of another embodiment of a refrigerant service system having a combination heat exchanger and compressor oil separator located within the accumulator. 
           [0029]      FIG. 8  is a bottom view of the manifold block of the refrigerant service system of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    For the purposes of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. No limitation to the scope of the subject matter is intended by the references. This disclosure also includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the described embodiments as would normally occur to one skilled in the art to which this document pertains. 
         [0031]      FIG. 1  is a schematic diagram of a refrigerant service cart  100  for servicing an air conditioning system. The refrigerant service system  100  includes a manifold  104 , a compressor  106 , a controller  108 , and an oil drain receptacle  110 . The system  100  also includes a refrigerant input hose  112  configured to receive refrigerant, typically from a vehicle being serviced or an external storage vessel (not shown), and a refrigerant discharge hose  116  connecting the manifold  104  to a refrigerant storage tank  118 , also referred to as an internal storage vessel or ISV. The system  100  further includes a compressor suction hose  120 , a compressor discharge tube  124 , and a compressor oil return hose  128  connecting the manifold  104  to the compressor  106 . An oil drain tube  132  connects the manifold  104  to the system oil drain receptacle  110 . In some embodiments, the refrigerant service system  100  is contained entirely within a portable cart (not shown) to enable simple transportation and connection of the system  100  to an air conditioning system. 
         [0032]    The manifold  104  includes an accumulator  138 , in which a compressor oil separator  140  is mounted, a filter and dryer unit  142 , an oil return solenoid valve  144 , an oil drain solenoid valve  148 , a high pressure switch  152 , and a transducer  154 . The manifold  104  further includes a variety of connecting conduits bored within the block  134  to connect the various components of the manifold  104  to the hoses and tubes discussed above. A refrigerant input conduit  156  connects the refrigerant input hose  112  to the accumulator  138 . A compressor suction conduit  160  carries refrigerant from the accumulator  138  to the filter and dryer  142  and to the compressor suction hose  120 , while a compressor discharge conduit  164  carries refrigerant from the compressor discharge tube  124  to the compressor oil separator  140 . A refrigerant discharge conduit  168  fluidly connects the compressor oil separator  140  to the refrigerant discharge tube  116 . A compressor oil return conduit  172  carries compressor oil from the compressor oil separator  140  to the compressor oil return hose  128 , and a system oil drain  176  connects the system oil drain solenoid valve  148  to the system oil drain tube  132 . 
         [0033]    Referring to  FIGS. 2 and 3 , the manifold  104  includes a lower manifold block  134  and an upper manifold block  136 . The accumulator  138  and the filter and dryer unit  142  are mounted to an exterior of the lower manifold block  134  within an accumulator port  178  ( FIG. 5 ) and a filter and dryer port  179  ( FIG. 5 ), respectively. The system oil drain solenoid  148  is mounted to the bottom of the accumulator  138 . 
         [0034]      FIG. 4  is a cross-sectional view of the accumulator  138  and the compressor oil separator  140 . The accumulator  138  includes an accumulator shell  180 , which defines an accumulator chamber  184  between the inner wall of the shell  180  and the exterior of the compressor oil separator  140 . 
         [0035]    With reference to  FIGS. 4 and 5 , the compressor oil separator  140  is mounted to the lower manifold block  134  within the accumulator shell  180  at a compressor oil separator connection  188  in the lower manifold block  134 . The compressor oil separator  140  includes a compressor oil separator body  192  defining a compressor oil separation chamber  196  therein, and a coalescing filter  200  within the compressor oil separator  140  and mounted to a coalescing filter port  190  of the lower manifold block  134 . At a lower portion of the compressor oil separation chamber  196 , a compressor oil collection region  204  funnels fluid into a compressor oil outlet passage  208  defined in the oil separator body  192 , and the compressor oil outlet passage  208  connects the compressor oil separation chamber  196  to the compressor oil return conduit  172 . Inner O-ring  212  and outer O-ring  216  seal the compressor oil separator body  192  against the lower manifold block  134  to seal the compressor oil separation chamber  140  and the accumulator chamber  184 , respectively, from the compressor oil return conduit  172 . In the illustrated embodiment, the outer surface of the compressor oil separator body  192  has a plurality of fins  220  (shown in  FIGS. 4 and 6 ) to increase the outer surface area of the compressor oil separator body  192 , though in other embodiments the outer surface of the compressor oil separator body has different surface features or is smooth. 
         [0036]    As is illustrated in  FIG. 5 , the lower manifold block  134  includes a deep recovery inlet  224  and a tank fill inlet  228  inside an area bounded by the accumulator mount  178 . Outside of the area bounded by the accumulator mount  178 , the bottom surface of the lower manifold block  134  includes a datum through hole  232  and two pressure transducer ports  236 ,  240 . 
         [0037]    The controller  108  is operatively connected to the compressor  106 , the compressor oil return solenoid valve  144 , the system oil drain solenoid valve  148 , and the pressure transducer  154 . The controller  108  is configured to selectively activate the solenoid valves  144 ,  148  and the compressor  106 . The pressure transducer  154  is configured to transmit a signal indicative of the pressure within the accumulator chamber  184  to the controller  108 . 
         [0038]    Operation and control of the various components and functions of the refrigerant recharge system  100  are performed with the aid of the controller  108 . The controller  108  is implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions are stored in a memory unit associated with the controller  108 . The processors, memory, and interface circuitry configure the controller  108  to perform the functions described above and the processes described below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. 
         [0039]    In use, an operator connects the refrigerant service system  100  to service ports of an air conditioning system, for example a vehicle air conditioning system, to initiate a refrigerant recovery operation. The controller  108  activates a series of valves (not shown) between the refrigerant input hose  112  and the air conditioning system to open the path from the air conditioning system to the refrigerant input hose to remove refrigerant from the air conditioning system. The refrigerant flows through the refrigerant input hose  112  and into the refrigerant input conduit  156  in the manifold  104 . The refrigerant then enters the accumulator chamber  184 , where the heat from the compressor oil separator  140  vaporizes the refrigerant. A small amount of system oil is typically entrained in the refrigerant during normal use in the air conditioning system. The system oil has a higher boiling point than the refrigerant, and therefore remains in a liquid phase and falls to the bottom of the accumulator  138  under the force of gravity as the refrigerant is vaporized. The system oil accumulates at the bottom of the accumulator chamber  184  until the system oil drain solenoid valve  148  is opened and the system oil flows through the oil drain  176  and the system oil drain tube  132  into the system oil drain receptacle  110 . 
         [0040]    The controller  108  activates the compressor  106  to generate a negative pressure in the compressor suction hose  120  and compressor suction conduit  160 , pulling the vaporized refrigerant in the accumulator chamber  184  through the filter and dryer unit  142 . The filter and dryer unit  142  removes moisture and other contaminants present in the refrigerant. The refrigerant continues through the compressor suction conduit  160  and the compressor suction hose  120  into the compressor  106 . The compressor  106  pressurizes the refrigerant and forces the refrigerant through the compressor discharge tube  124  back into the compressor discharge conduit  164  in the manifold  104 . The high pressure switch  152  is located in the compressor discharge conduit  164  and is configured to deactivate the compressor if the pressure downstream of the compressor  106  exceeds a threshold value to prevent excess pressure in the components downstream of the compressor  106 . During the pass through the compressor  106 , the temperature of the refrigerant increases substantially, such that the refrigerant in the compressor discharge conduit  164  is hotter than the refrigerant coming into the system. 
         [0041]    The heated and pressurized refrigerant then enters the coalescing filter  200  in the compressor oil separator  140 . The hot refrigerant in the compressor oil separator  140  transfers heat to the compressor oil separator body  192 , heating the compressor oil separator body  192 . The compressor oil separator body  192  transfers heat to the refrigerant and oil in the accumulator chamber  184  to assist in vaporizing the refrigerant entering the accumulator  138 . The compressor oil separator  140  therefore also serves as a heat exchanger within the accumulator  138 . 
         [0042]    During the pass through the compressor  106 , a small quantity of compressor oil may be entrained in the refrigerant. As the refrigerant enters the compressor oil separator  140 , the heat removed from the refrigerant vapor causes the compressor oil, which has a lower condensation temperature than the refrigerant, to condense in the compressor oil separation chamber  196 . The fine liquid oil particles coalesce on the coalescing filter  200  and, once large enough, drip downwardly to the compressor oil collection region  204 . The refrigerant vapor, now free of compressor oil, passes into the refrigerant discharge conduit  168  and then into the refrigerant discharge hose  116  to be stored in the refrigerant storage tank  118  or otherwise reused. 
         [0043]    The system  100  is also configured to periodically initiate a system oil drain process when a recovery operation is in progress. During the system oil drain process, the controller  108  deactivates the compressor  106  and activates the solenoid valve  144  to open, linking the accumulator chamber  184  to the compressor  106  through the compressor oil return conduit  172 . The compressor oil return hose  128  is connected to the compressor suction hose  120  through the compressor  106 , and therefore opening the solenoid valve  144  fluidly connects the accumulator chamber  184  to the compressor oil separator chamber  196  through the compressor suction conduit  160 , the compressor suction hose  120 , the compressor  106 , the compressor oil return hose  128 , and the compressor oil return conduit  172 . Refrigerant remaining in the compressor oil separator chamber  196  and compressor discharge conduit  164  is at a higher pressure than the accumulator chamber  184  due to being previously passed through the compressor  106 . As a result, the refrigerant travels from the compressor oil separator chamber  196  and compressor discharge conduit  164  into the accumulator chamber  184 , increasing the pressure in the accumulator chamber  184 . The pressure transducer  152  senses the pressure in the accumulator chamber  184 , and once the pressure in the accumulator chamber  184  reaches a predetermined threshold, the controller  108  operates the compressor oil return solenoid valve  144  to close and the system oil drain solenoid valve  148  to open. In some embodiments, the solenoid valve  144  remains open while the oil drain solenoid valve  148  is opened. 
         [0044]    The increased pressure in the accumulator chamber  184  forces system oil in the accumulator chamber  184  through the system oil drain  176  and oil drain tube  132  into the system oil drain receptacle  110 . The controller  108  is configured to monitor the pressure signal generated by the transducer  152  and close the system oil drain solenoid valve  148  upon detection of spike in pressure in the accumulator chamber  184  indicating that the system oil has been removed from the chamber  184 . In some embodiments, the system oil is removed from the accumulator chamber  184  by gravity, without additional pressure, once the system oil drain solenoid valve  148  is opened. 
         [0045]    During the refrigerant recovery operation, the system  100  periodically initiates a compressor oil return process to return compressor oil collected in the compressor oil separation chamber  196  to the compressor  106 . During the refrigerant recovery operation, the compressor  106  generates a constant suction in the compressor oil return conduit  172 . To recover the compressor oil, the controller  108  operates the compressor oil return solenoid valve  144  to open, enabling flow through the compressor oil return conduit  172 . The suction in the compressor oil return conduit  172  combined with the overpressure in the compressor oil separator chamber  184  urges the compressor oil collected in the compressor oil collection region  204  through the compressor oil outlet passage  208 . The compressor oil then flows through the compressor oil return conduit  172  and the compressor oil return hose  128  back into the compressor  106 . 
         [0046]      FIGS. 7 and 8  illustrate another embodiment of a combined accumulator  300  and compressor oil separator  304  for use in place of the accumulator  138  in the system  100  of  FIG. 1 . The accumulator  300  is attached to a lower manifold block  308  at an accumulator mount  348 . The lower manifold block  308  of the embodiment of  FIGS. 7 and 8  is configured similar to the lower manifold block  134  discussed above, though some of the connections are positioned in different locations. The accumulator  300  includes an accumulator shell  312 , which defines an accumulator chamber  316  between the inner wall of the shell  312  and the exterior of the compressor oil separator  304 . The accumulator  300  further includes an input injection tube  320  connected to the input conduit  156  and the input hose  112  of the manifold  104  ( FIG. 1 ). 
         [0047]    The compressor oil separator  304  is mounted to the lower manifold block  308 , within the accumulator shell  312 , at a compressor oil separator connection  352 . The compressor oil separator  304  includes an oil separator body  324  defining a compressor oil separation chamber  328  therein, and a coalescing filter  332  mounted to the lower manifold block  308  at a coalescing filter port  356 . At a lower portion of the compressor oil separation chamber  328 , a compressor oil collection region  336  collects the compressor oil in the oil separation chamber  328 . A compressor oil suction tube  340  is positioned with an open end in the compressor oil collection region  336 , and its other end connected to the compressor oil return conduit  172  of the manifold  104  ( FIG. 1 ). An elastomeric seal, for example an  0 -ring  344 , seals the compressor oil separator body  324  against the lower manifold block  308  to seal the compressor oil separation chamber  328  from the accumulator chamber  316 . In the embodiment of  FIG. 7 , the outer surface of the oil separator body  324  is smooth to facilitate system oil travelling down the outer surface under the force of gravity. 
         [0048]      FIG. 8  depicts the bottom side of the lower manifold block  308 , illustrating the connection ports in the bottom of the lower manifold block  308 . The lower manifold block  308  includes a filter and dryer port  360  for connection of the filter and dryer unit  142 . The view of  FIG. 8  also illustrates the positions of the input conduit  156 , the compressor suction conduit  160 , the compressor discharge conduit  164 , the refrigerant discharge conduit  168 , and the compressor oil return conduit  172 . Within an area in which the accumulator  300  is connected, the lower manifold block  308  includes a deep recovery inlet  364 , a recycling inlet  368 , an identifier recovery inlet  372 , and a tank fill inlet  376 . The exterior of the bottom surface of the lower manifold block  308  also has a datum through hole  380  and two pressure transducer ports  384 ,  388 . 
         [0049]    The operation of the embodiment of  FIGS. 7-8  is substantially identical to that of the embodiment discussed above with regard to  FIGS. 1-6 . After commencing a refrigerant recovery operation, refrigerant from the air conditioning system is passed through the refrigerant input hose  112  and into the refrigerant input conduit  156  in the manifold  104 . The refrigerant then enters the accumulator chamber  316  through the input injection tube  320 , which directs the incoming refrigerant onto the smooth outer surface of the compressor oil separator body  324 . Heat from the compressor oil separator  304  assists in vaporizing the refrigerant, while system oil in the refrigerant remains in a liquid phase and flows down the smooth outer surface of the compressor oil separator body  324  under the force of gravity. The system oil drips off the compressor oil separator  304  and accumulates at the bottom of the accumulator chamber  316  until a system oil drain process is initiated. 
         [0050]    The compressor  106  generates a negative pressure in the compressor suction hose  120  and compressor suction conduit  160 , pulling the vaporized refrigerant in the accumulator chamber  316  through the filter and dryer unit  142 , which removes moisture and other contaminants present in the refrigerant. The refrigerant continues through the compressor suction conduit  160  and the compressor suction hose  120  into the compressor  106 , where the refrigerant is pressurized and the temperature of the refrigerant increases. The heated and pressurized refrigerant then travels through the compressor discharge tube  124  back into the compressor discharge conduit  164  in the manifold  104 . The high pressure switch  152  is located in the compressor discharge conduit  164  and is configured to automatically deactivate the compressor  106  if the pressure downstream of the compressor  106  exceeds a threshold value to prevent an overcharge condition of the compressor  106 . 
         [0051]    During the pass through the compressor  106 , a small quantity of compressor oil may be entrained in the refrigerant. As the refrigerant enters the compressor oil separator  304 , the heat removed from the refrigerant vapor causes the compressor oil, which has a lower condensation temperature than the refrigerant, to condense in the compressor oil separator chamber  328 . The fine liquid oil particles coalesce on the coalescing filter  332  and, once large enough, drip downwardly to the compressor oil collection region  336 . The refrigerant vapor, now free of compressor oil, passes into the compressor oil separator chamber  328 , to the refrigerant discharge conduit  168 , and into the refrigerant discharge hose  116  to be stored in the refrigerant storage tank  118  or otherwise reused. 
         [0052]    The heated refrigerant in the compressor oil separator chamber  328  transfers heat to the compressor oil separator body  324 , which passes heat to the refrigerant injected through the input injection tube  320  onto the outer surface of the compressor oil separator body  324  in the accumulator chamber  316 . The compressor oil separator  304  therefore also serves as a heat exchanger within the accumulator  300 . 
         [0053]    The system  100  is also configured to periodically initiate a system oil drain process when the refrigerant recovery operation is in progress. During the system oil drain process, the controller  108  deactivates the compressor  106  and activates the compressor oil return solenoid valve  144  to open, linking the accumulator chamber  316  to the compressor  106  through the compressor oil return conduit  172 . The compressor oil return hose  128  is connected to the compressor suction hose  120  through the compressor  106 , and therefore opening the compressor oil return solenoid valve  144  fluidly connects the accumulator chamber  316  to the compressor oil separator chamber  328  through the compressor suction conduit  160 , the compressor suction hose  120 , the compressor  106 , the compressor oil return hose  128 , and the compressor oil return conduit  172 . Refrigerant remaining in the compressor oil separator chamber  328  and the compressor discharge conduit  164  has a higher pressure than the accumulator chamber  316  due to being previously passed through the compressor  106 . As a result, the refrigerant travels from the compressor oil separator chamber  328  and compressor discharge conduit  164  into the accumulator chamber  316 , increasing the pressure in the accumulator chamber  316 . The pressure transducer  154  senses the pressure in the accumulator chamber  316 , and once the pressure in the accumulator chamber  316  reaches a predetermined threshold, the controller  108  operates the compressor oil return solenoid valve  144  to close and the system oil drain solenoid valve  148  to open. In some embodiments, the compressor oil return solenoid valve  144  remains open while the system oil drain solenoid valve  148  is opened. 
         [0054]    The increased pressure in the accumulator chamber forces system oil in the accumulator chamber  316  through the oil drain  176  and oil drain tube  132  into the oil drain receptacle  110 . The controller  108  continues to monitor the pressure signal generated by the transducer  152 , and closes the oil drain solenoid valve  148  upon detection of a spike in pressure in the accumulator chamber  316  indicating that the oil has been removed from the chamber  316 . In some embodiments, the accumulator chamber  316  is not pressurized during a system oil recovery operation, and the system oil is recovered by opening the system oil drain solenoid valve  148  and allowing the oil to drain by gravity to the system oil drain receptacle  110 . 
         [0055]    During the refrigerant recovery operation, the system  100  periodically initiates a compressor oil return process to return compressor oil collected in the compressor oil separation chamber  328  to the compressor  106 . During the refrigerant recovery operation, the compressor  106  generates a constant suction in the compressor oil return conduit  172 . To recover the compressor oil, the controller  108  operates the compressor oil return solenoid valve  144  to open, enabling flow through the compressor oil return conduit  172 . The suction in the compressor oil return conduit  172  combined with the overpressure in the compressor oil separator chamber  324  urges the compressor oil in the collection region  336  into the compressor oil suction tube  340 . The compressor oil then flows through the compressor oil return conduit  172  and the compressor oil return hose  128  back into the compressor  106 . 
         [0056]    It will be appreciated that variants of the above-described and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the foregoing disclosure.