Patent Publication Number: US-10775084-B2

Title: System for refrigerant charge verification

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/193,568, filed on Feb. 28, 2014, which claims the benefit of U.S. Provisional Application No. 61/789,913, filed on Mar. 15, 2013. The entire disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to refrigeration systems and more specifically to a charge-verification system for use with a refrigeration system. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Compressors are used in a wide variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically referred to as “refrigeration systems”) to provide a desired heating and/or cooling effect. In any of the foregoing systems, the compressor should provide consistent and efficient operation to ensure that the particular refrigeration system functions properly. 
     Refrigeration systems and associated compressors may include a protection system that selectively restricts power to the compressor to prevent operation of the compressor and associated components of the refrigeration system (i.e., evaporator, condenser, etc.) when conditions are unfavorable. The types of faults that may cause protection concerns include electrical, mechanical, and system faults. Electrical faults typically have a direct effect on an electrical motor associated with the compressor, while mechanical faults generally include faulty bearings or broken parts. Mechanical faults often raise a temperature of working components within the compressor and, thus, may cause malfunction of and possible damage to the compressor. 
     In addition to electrical and mechanical faults associated with the compressor, the compressor and refrigeration system components may be affected by system faults attributed to system conditions such as an adverse level of fluids (i.e., refrigerant) disposed within the system or a blocked-flow condition external to the compressor. Such system conditions may raise an internal compressor temperature or pressure to high levels, thereby damaging the compressor and causing system inefficiencies and/or failures. 
     SUMMARY 
     A charge-verification tool is provided for use with a charge-verification system to diagnose and remedy a charge condition. The charge-verification tool includes a device having a controller configured to communicate with a system controller in the charge-verification system and a display configured to display measurements and instructions to an installer. The device is a user interface and is configured to provide communication between the installer and the system controller in the charge-verification system. The controller prompts the installer to input charge-verification system information including refrigeration line length and diameter. The controller receives a subcooling temperature calculated by the system controller and determines whether the subcooling temperature is between a threshold and a target subcooling temperature. The controller displays an amount of charge to add to the charge-verification system based on whether the subcooling temperature is between the threshold and the target subcooling temperature. 
     The charge-verification tool may further include the controller displaying a system stabilization indication received from the system controller when the charge-verification system stabilizes after startup and after the installer adds charge to the charge-verification system. 
     The charge-verification tool may further include the controller displaying the subcooling temperature and the target subcooling temperature on the display. 
     The charge-verification tool may further include the controller displaying a “done” indication if the subcooling temperature is equal to the target subcooling temperature. 
     The charge-verification tool may further include the controller determining that an undercharge condition exists if the subcooling temperature is between the threshold and the target subcooling temperature. 
     The charge-verification tool may further include the controller determining that an overcharge condition exists if the subcooling temperature is greater than the target subcooling temperature. 
     The charge-verification tool may further include the controller displaying a negative amount of charge to add to the charge-verification system, indicating that charge should be removed from the system, if the overcharge condition exists. 
     The charge-verification tool may further include a threshold that is two degrees Fahrenheit. 
     The charge-verification tool may further include a target subcooling temperature that is ten degrees. 
     The charge-verification tool may further include the controller determining the subcooling temperature based on at least two of a saturated condensing temperature, a liquid line temperature, a first coil temperature, and a second coil temperature. 
     In another configuration, a method of charge verification for use with a charge-verification system to diagnose and remedy a charge condition, is provided. The method includes prompting, by a device controller, an installer to input charge-verification system information including refrigeration line length and diameter; receiving, by the device controller, a subcooling temperature calculated by a system controller for the charge-verification system; determining, by the device controller, whether the subcooling temperature is between a threshold and a target subcooling temperature; and displaying, by the device controller, an amount of charge to add to the charge-verification system based on whether the subcooling temperature is between the threshold and the target subcooling temperature. 
     The method may further include displaying, by the device controller, a system stabilization indication received from the system controller when the charge-verification system stabilizes after startup and after the installer adds charge to the charge-verification system. 
     The method may further include displaying, by the device controller, the subcooling temperature and the target subcooling temperature on the display. 
     The method may further include displaying, by the device controller, a “done” indication if the subcooling temperature is equal to the target subcooling temperature. 
     The method may further include determining an undercharge condition if the subcooling temperature is between the threshold and the target subcooling temperature. 
     The method may further include determining an overcharge condition if the subcooling temperature is greater than the target subcooling temperature. 
     The method may further include displaying, by the device controller, a negative amount of charge to add to the charge-verification system, indicating that charge should be removed from the system, if the overcharge condition exists. 
     The method may further include wherein the threshold is two degrees Fahrenheit and the target subcooling temperature is ten degrees. 
     The method may further include prompting the installer to add the charge in two increments if the amount of charge to be added to the charge-verification system is greater than a predetermined threshold. 
     The method may further include determining the subcooling temperature based on at least two of a saturated condensing temperature, a liquid line temperature, a first coil temperature, and a second coil temperature. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic representation of charge-verification system in accordance with the principles of the present disclosure implemented in a refrigeration system; 
         FIG. 2  is a graph showing coil temperature versus a percentage position of the coil circuit length during a normal charge condition according to the present disclosure; 
         FIG. 3  is a graph showing coil temperature versus a percentage position of the coil circuit length during an overcharge condition according to the present disclosure; 
         FIG. 4  is a graph showing coil temperature versus a percentage position of the coil circuit length during an undercharge condition according to the present disclosure; 
         FIG. 5  is a graph showing coil temperature versus a percentage position of the coil circuit length for two coil temperature sensors mounted at approximately forty percent and seventy percent, respectively, of the coil circuit length according to the present disclosure; 
         FIG. 6  is a flow chart detailing operation of a charge-verification system according to the present disclosure; 
         FIG. 7  is a flow chart detailing operation of a charge-verification system accordingly to the present disclosure; 
         FIG. 8  is a flow chart detailing operation of a device that may operate one or both of the charge-verification systems of  FIGS. 6 and 7 ; and 
         FIG. 9  is a bar graph showing various combinations of condenser temperature difference (TD), subcooling (SC), and approach temperature (AT) at different temperature and refrigerant charge conditions. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     With reference to  FIG. 1 , a charge-verification system  10  is provided. The charge-verification system  10  may be used in conjunction with a refrigeration system  12  including a compressor  14 , a condenser  18 , an evaporator  22 , and an expansion valve  26 . While the refrigeration system  12  is described and shown as including a compressor  14 , a condenser  18 , an evaporator  22 , and an expansion valve  26 , the refrigeration system  12  may include additional and/or alternative components. Further, the present disclosure is applicable to various types of refrigeration systems including, but not limited to, heating, ventilating, air conditioning (HVAC), heat pump, refrigeration, and chiller systems. 
     During operation of the refrigeration system  12 , the compressor  14  circulates refrigerant generally between the condenser  18  and the evaporator  22  to produce a desired heating and/or cooling effect. Specifically, the compressor  14  receives refrigerant in vapor form through an inlet fitting  30  and compresses the refrigerant. The compressor  14  provides pressurized refrigerant in vapor form to the condenser  18  via a discharge fitting  34 . 
     All or a portion of the pressurized refrigerant received from the compressor  14  may be converted into the liquid state within the condenser  18 . Specifically, the condenser  18  transfers heat from the refrigerant to the surrounding air, thereby cooling the refrigerant. When the refrigerant vapor is cooled to a temperature that is less than a saturation temperature, the refrigerant changes state from a vapor to a liquid. The condenser  18  may include a condenser fan  38  that increases the rate of heat transfer away from the refrigerant by forcing air across a heat-exchanger coil associated with the condenser  18 . The condenser fan  38  may be a variable-speed fan that is controlled by the charge-verification system  10  based on a cooling demand. 
     The refrigerant passes through the expansion valve  26  prior to reaching the evaporator  22 . The expansion valve  26  expands the refrigerant prior to the refrigerant reaching the evaporator  22 . A pressure drop caused by the expansion valve  26  may cause a portion of the liquefied refrigerant to change state from a liquid to a vapor. In this manner, the evaporator  22  may receive a mixture of vapor refrigerant and liquid refrigerant. 
     The refrigerant absorbs heat in the evaporator  22 . Accordingly, liquid refrigerant disposed within the evaporator  22  changes state from a liquid to a vapor when warmed to a temperature that is greater than or equal to the saturation temperature of the refrigerant. The evaporator  22  may include an evaporator fan  42  that increases the rate of heat transfer to the refrigerant by forcing air across a heat-exchanger coil associated with the evaporator  22 . The evaporator fan  42  may be a variable-speed fan that is controlled by the charge-verification system  10  based on a cooling demand. 
     As the liquid refrigerant absorbs heat, the ambient air disposed proximate to the evaporator  22  is cooled. The evaporator  22  may be disposed within a space to be cooled such as a building or refrigerated case where the cooling effect produced by the refrigerant absorbing heat is used to cool the space. The evaporator  22  may also be associated with a heat-pump refrigeration system where the evaporator  22  may be located remote from the building such that the cooling effect is lost to the atmosphere and the rejected heat generated by the condenser  18  is directed to the interior of a space to be heated. 
     A system controller  46  may be associated with the charge-verification system  10  and/or the compressor  14  and may monitor, control, protect, and/or diagnose the compressor  14  and/or the refrigeration system  12 . The system controller  46  may utilize a series of sensors to determine both measured and non-measured operating parameters of the compressor  14  and/or the refrigeration system  12 . While the system controller  46  is shown as being associated with the compressor  14 , the system controller  46  could be located anywhere within or outside of the refrigeration system  12 . The system controller  46  may use the non-measured operating parameters in conjunction with the measured operating parameters to monitor, control, protect, and/or diagnose the compressor  14  and/or the refrigeration system  12 . Such non-measured operating parameters may also be used to check the sensors to validate the measured operating parameters and to determine a refrigerant charge level and/or a fault of the refrigeration system  12 . 
     The system controller  46  may control the condenser fan  38  and the evaporator fan  42  such that operation of the condenser fan  38  and the evaporator fan  42  is coordinated with operation of the compressor  14 . For example, the system controller  46  may control one or both fans  38 ,  42  to operate at a full or reduced speed depending on the output of the compressor  14 . 
     The condenser  18 , having an inlet  50  and an outlet  54 , may further include a first coil temperature sensor  58  and a second coil temperature sensor  62  positioned on first and second heat-exchanger coil circuit tubes (not shown). The first coil temperature sensor  58  may be located within a first predetermined range of the coil circuit length from the condenser inlet  50 . For example, the first coil temperature sensor  58  may be located at approximately forty percent of the coil circuit length from the condenser inlet  50  or at any location between thirty percent and fifty percent of the coil circuit length from the condenser inlet  50 . The second coil temperature sensor  62  may be located within a second predetermined range of the coil circuit length from the condenser inlet  50 . For example, the second coil temperature sensor  62  may be located at approximately seventy percent of the coil circuit length from the condenser inlet  50  or at any location between sixty percent and ninety percent of the coil circuit length from the condenser inlet  50 . The first and second coil temperature sensors  58 ,  62  detect a temperature of the refrigerant circulating in the condenser  18  and may be used by the system controller  46  of the charge-verification system  10  to determine a saturated condensing temperature (SCT) of the refrigerant. 
     While the condenser  18  is illustrated as a Plate-Fin Heat Exchanger Coil, the present disclosure is applicable to other heat exchangers such as a smaller 5 mm microtube, a Microchannel, Spine-Fin Heat Exchanger Coils, or other heat exchangers known in the art. Further, the condensing coil may include various different parallel circuits with different heat exchanger designs. The first and second coil temperature sensors  58 ,  62  may be associated with any of the heat exchangers of the various parallel circuits. 
     A liquid-line temperature sensor  66  may be located along a conduit  70  extending between the condenser  18  and the expansion valve  26  and may provide an indication of a temperature of the liquid refrigerant within the refrigeration system  12  or liquid-line temperature (LLT) to the system controller  46 . While the liquid-line temperature sensor  66  is described as being located along the conduit  70  extending between the condenser  18  and the expansion valve  26 , the liquid-line temperature sensor  66  could alternatively be placed anywhere within the refrigeration system  12  that allows the liquid-line temperature sensor  66  to provide an indication of a temperature of liquid refrigerant within the refrigeration system  12  to the system controller  46 . 
     An outdoor/ambient temperature sensor  74  may be located external to the compressor  14  and generally provides an indication of the outdoor/ambient temperature (OAT) adjacent to the compressor  14  and/or the charge-verification system  10 . The outdoor/ambient temperature sensor  74  may be positioned adjacent to the compressor  14  such that the outdoor/ambient temperature sensor  74  is in close proximity to the system controller  46 . Placing the outdoor/ambient temperature sensor  74  in close proximity to the compressor  14  provides the system controller  46  with a measure of the temperature generally adjacent to the compressor  14 . While the outdoor/ambient temperature sensor  74  is described as being located adjacent to the compressor  14 , the outdoor/ambient temperature sensor  74  could be placed anywhere within the refrigeration system  12  that allows the outdoor/ambient temperature sensor  74  to provide an indication of the outdoor/ambient temperature proximate to the compressor  14  to the system controller  46 . Additionally, or alternatively, local weather data could be retrieved using the internet, for example, to determine ambient temperature. 
     The system controller  46  receives sensor data from the coil temperature sensors  58 ,  62 , the liquid-line temperature sensor  66 , and the outdoor/ambient temperature sensor  74  for use in controlling and diagnosing the refrigeration system  12  and/or the compressor  14 . The system controller  46  may additionally use the sensor data from the respective sensors  58 ,  62 ,  66 , and  74  to determine non-measured operating parameters of the refrigeration system  12  and/or the compressor  14  using the relationships shown in  FIGS. 3, 4, 5, 6, and 7 . 
     The system controller  46  determines which of the temperatures received from the first coil temperature sensor  58  and the second coil temperature sensor  62  is closer to the actual SCT and uses that sensor in conjunction with the temperature reading from the liquid-line temperature sensor  66  to determine a subcooling and the charge level of the refrigeration system  12 , as will be described in greater detail below. 
     With particular reference to  FIG. 2 , a graph showing coil temperature versus a percentage position of the coil circuit length during a normal charge condition is illustrated. Upon exiting the condenser  18 , approximately ten to twenty percent of the refrigerant is in a gaseous state or de-superheating phase, approximately ten to twenty percent of the refrigerant is in a liquid state or subcooling phase, and the remaining sixty to seventy percent of the refrigerant is in a liquid/vapor state or two-phase condensing state. The subcooling phase typically yields approximately ten degrees Fahrenheit (10° F.) subcooling and is considered a normal charge level. 
     When the charge-verification system  10  operates under normal charge conditions, placement of the temperature sensor on a coil circuit tube at approximately a midpoint of the condenser  18  provides the system controller  46  with an indication of the temperature of the condenser  18  that approximates the saturated condensing temperature and saturated condensing pressure. When the charge-verification system  10  is normally charged such that the refrigerant within the refrigeration system  12  is within +/−fifteen percent of an optimum-charge condition, the information detected by the temperature sensor positioned at approximately the midpoint of the coil circuit tube is closer to the actual SCT. 
     With particular reference to  FIG. 3 , a graph showing coil temperature versus a percentage position of the coil circuit length during an overcharge condition is illustrated. An overcharge condition may exist when the subcooling temperature is greater than approximately thirty degrees Fahrenheit (30° F.). When the condenser  18  is in an overcharge state, the coil mid-point temperature may already be subcooled, thus providing a much lower value than actual SCT based on pressure. An excess amount of refrigerant may be disposed within the refrigeration system  12 , as the refrigerant disposed within the condenser  18  changes state from a gas to a liquid before reaching the midpoint of the condenser  18 . 
     The refrigerant exiting the compressor  14  and entering the condenser  18  is at a reduced temperature and may be in an approximately 40/60 gas/liquid mixture. The reduced-temperature refrigerant converts from the vapor state to the liquid state at an earlier point along the length of the condenser  18  and therefore may be at a partial or fully liquid state when the refrigerant approaches the temperature sensor disposed at the midpoint of the condenser  18 . Because the refrigerant is at a lower temperature, the temperature sensor at the midpoint reports a temperature to the system controller  46  that is lower than the actual SCT. 
     When the refrigeration system  12  operates in the overcharge condition, the subcooled liquid phase increases and the reading of the second coil temperature sensor  62  may be lower than the reading of the first coil temperature sensor  58  because the tube where the second coil temperature sensor is located is subcooled compared to the tube where the first coil temperature sensor is located. Therefore, during an overcharge condition, the temperature from the first coil temperature sensor  58  is closer to the actual SCT than the temperature from the second coil temperature sensor  62 . 
     With particular reference to  FIG. 4 , a graph showing coil temperature versus a percentage position of the coil circuit length during an undercharge condition is illustrated. An undercharge condition may exist when the subcooling temperature is less than zero degrees Fahrenheit (0° F.). When the condenser  18  is in an undercharge state, any coil circuit tube after approximately the twenty percent de-superheating phase adequately measures the actual SCT temperature because the remaining portion of the condenser  18  is in two-phase condensing without any subcooled liquid phase. 
     When the refrigeration system  12  operates in the undercharge condition, the subcooled liquid phase decreases and the reading of the second coil temperature sensor  62  may approach the reading of the outlet liquid-line temperature sensor  66 . Eventually, when the subcooling phase disappears because both sensors  58 ,  62  are detecting only the condensing phase, the readings of temperature sensors  58 ,  62  are approximately equal. In this situation, the temperature from the first coil temperature sensor  58  approximately equals the temperature from the second coil temperature sensor  62 , which, in turn, approximates the actual SCT. 
     With reference to  FIG. 5 , a graph showing coil temperature versus a percentage position of the coil circuit length is illustrated. The positions of the first and second coil temperature sensors  58 ,  62  along a length of the condenser  18  are schematically represented by vertical lines at approximately thirty percent (30%) and seventy percent (70%), respectively. Each plotted line on the graph represents a different charge condition. Intersection between the plotted lines and the respective vertical lines of the first and second coil temperature sensors  58 ,  62  may be used by the controller  46  to identify amongst the various charge conditions. 
     In the condensing phase, the temperature changes mainly as a function of pressure drop; thus, the temperature changes very gradually, at approximately less than three degrees (3° F.) per coil circuit. When in the subcooled phase, the temperature changes much more rapidly, at approximately greater than ten degrees (10° F.) per coil circuit. 
     When the temperature from the first coil temperature sensor  58  is greater than the temperature from the second coil temperature  62  sensor plus approximately two degrees Fahrenheit (2° F.) and both are greater than the LLT plus approximately seven degrees Fahrenheit (7° F.) (Tcoil 1 &gt;Tcoil 2 +2° F.&gt;LLT+7° F.), a normal charge condition is declared. When the temperature from the first coil temperature sensor  58  is approximately equal to the temperature from the second coil temperature sensor  62 —which is approximately equal to the LLT (Tcoil 1 ≅Tcoil 2 ≅LLT)—an undercharge condition is declared; indicating that refrigerant should be added to the system. When the temperature from the first coil temperature sensor  58  is greater than the temperature from the second coil temperature sensor  62  plus approximately five degrees Fahrenheit (5° F.) and both are greater than the LLT plus approximately two degrees Fahrenheit (2° F.) (Tcoil 1 &gt;Tcoil 2 +5° F.&gt;LLT+2° F.), an overcharge condition is declared; indicating that refrigerant should be removed from the system. 
     For example, when the refrigeration system  12  is operating in an undercharged condition, the first coil temperature sensor  58  may be reporting eighty-four degrees Fahrenheit (84° F.), eighty-nine degrees Fahrenheit (89° F.), or ninety-five degrees Fahrenheit (95° F.) and the second coil temperature sensor  62  may be reporting eighty-three degrees Fahrenheit (83° F.), eighty-nine degrees Fahrenheit (89° F.), or ninety-four degrees Fahrenheit (94° F.). If the first coil temperature sensor  58  is reporting eighty-four degrees Fahrenheit (84° F.) and the second coil temperature sensor  62  is reporting eighty-three degrees Fahrenheit (83° F.), the subcooling temperature is 3.2° F. If the first coil temperature sensor  58  is reporting eighty-nine degrees Fahrenheit (89° F.) and the second coil temperature sensor  62  is reporting eighty-nine degrees Fahrenheit (89° F.), the subcooling temperature is 0.7° F. If the first coil temperature sensor  58  is reporting ninety-five degrees Fahrenheit (95° F.) and the second coil temperature sensor  62  is reporting ninety-four degrees Fahrenheit (94° F.), the subcooling temperature is 0.3° F. The graph illustrates similar relations for normal operation and overcharged operation as well. The controller  46  may therefore use the data from the first coil temperature sensor  58  and the second coil temperature sensor  62  along with the LLT to diagnose the charge level of the system. 
     Based on the temperature readings from the first and second coil temperature sensors  58 ,  62 , the system controller  46  determines the subcooling temperature and the charge condition (as shown in  FIG. 5 ). Based on the subcooling temperature and the charge condition, the system controller  46  may determine remedial actions that may be necessary, such as addition of refrigerant to the system or removal of refrigerant from the system. 
     Dependent upon the amount of refrigerant that needs to be added or removed from the system, the refrigerant may be added or removed in a series of incremental additions or removals to ensure that too much refrigerant is not added or removed. Between each of the series of incremental additions or removals, the system controller  46  may determine the subcooling temperature and the charge condition. 
     Now referring to  FIG. 6 , a charge verification method  100  is illustrated. The charge verification method  100  may be performed by the controller  46  during operation of the refrigeration system  12 . 
     At  104 , the method  100  determines whether the Tcoil 1  equals the Tcoil 2  and whether both of these values are approximately equal to the LLT (Tcoil 1 =Tcoil 2 =LLT). If true, the method  100  determines that the refrigeration system  12  is operating in an undercharged condition at  106 . At step  108 , the method  100  recommends adding refrigerant to the system. The method  100  then returns to step  104  to continue evaluating the Tcoil 1 , the Tcoil 2 , and the LLT. 
     If false at step  104 , the method  100  determines whether a first coil temperature (Tcoil 1 ) is greater than a second coil temperature (Tcoil 2 ) plus approximately two degrees Fahrenheit (2° F.) and whether both of these values are greater than the LLT plus approximately seven degrees Fahrenheit (7° F.) (Tcoil 1 &gt;Tcoil 2 +2° F.&gt;LLT+7° F.) at  110 . If true, the method  100  determines that the refrigeration system  12  is operating in a normal charge condition at  112 . The method  100  returns to step  104  to continue evaluating the Tcoil 1 , the Tcoil 2 , and the LLT. 
     If false at step  104 , the method  100  moves to step  110  and if false at step  110 , the method  100  moves to step  114  and determines whether the Tcoil 1  is greater than the Tcoil 2  plus approximately five degrees Fahrenheit (5° F.) and whether both of these are greater than the LLT plus approximately two degrees Fahrenheit (2° F.) (Tcoil 1 &gt;Tcoil 2 +5° F.&gt;LLT+2° F.). If true, the method  100  determines that the refrigeration system  12  is operating in an overcharged condition at  116 . At  118 , the method  100  recommends removing refrigerant from the system. The method  100  then returns to step  104  to continue evaluating the Tcoil 1 , the Tcoil 2 , and the LLT. 
     If false at step  114 , the method  100  returns to step  104  to continue evaluating the Tcoil 1 , the Tcoil 2 , and the LLT. 
     With particular reference to  FIG. 7 , another charge-verification method  120  is provided. As with the charge-verification method  100 , the charge-verification method  120  may be performed by the controller  46  during operation of the refrigeration system  12 . 
     The charge-verification method  120  may be used by the controller  46  in conjunction with or in place of the charge-verification method  100  when determining the charge of the refrigeration system  12 . If the methods  100 ,  120  are used in conjunction with one another, the methods  100 ,  120  may independently determine the charge of the refrigeration system  12  (i.e., normal charge, undercharge, or overcharge) and may be used by the controller  46  to verify the results of each method  100 ,  120 . Namely, the result obtained by one of the methods  100 ,  120  may be used by the controller  46  to verify the result obtained by the other method  100 ,  120  by comparing the results obtained via each method  100 ,  120 . 
     At  122 , the method  120  determines whether the TD is less than approximately 0.75Y (i.e., 75% of Y) and whether a ratio of AT/TD is greater than approximately 90%, whereby the variable (Y) represents a predetermined desired TD value, which may be determined based on system efficiency. If true, the method  120  determines that the refrigeration system  12  is operating in an undercharged condition at  124 . At step  126 , the method  120  recommends adding refrigerant to the system. The method  120  then returns to step  122  to continue evaluating the system  12 . 
     If false at step  122 , the method  120  moves to step  128  and determines whether the TD is approximately equal to the predetermined desired TD value Y (i.e., +/−15% of Y) and whether the ratio of SC/TD is less than approximately 75%. If true, the method  120  determines that the refrigeration system  12  is operating in a normal charge condition at  130 . The method  120  returns to step  122  to continue evaluating the system  12 . 
     If false at step  122 , the method  120  moves to step  128  and if false at step  128 , the method  120  moves to step  132  and determines whether the TD is greater than approximately 1.5Y and whether a ratio of SC/TD is greater than approximately 90%. If true, the method  120  determines that the refrigeration system  12  is operating in an overcharged condition at  134 . At  136 , the method  120  recommends removing refrigerant from the system. The method  120  then returns to step  122  to continue evaluating the system  12 . 
     If false at step  132 , the method  120  returns to step  122  to continue evaluating the system  12 . 
     The controller  46  may execute the foregoing methods  100 ,  120  simultaneously. Further, while the controller  46  monitors the system  12  for the undercharge condition prior to the normal-charge condition and the overcharge condition, the controller  46  could perform operations  104 ,  110 ,  114  of method  100  and operations  122 ,  128 ,  132  of method  120  in any order. The controller  46  is only described as performing operations  104  and  122  first, as most commercial refrigeration systems  12  are manufactured and shipped with a small volume of refrigerant and, therefore, are typically in the undercharge condition when initially installed. 
     In another configuration, the system controller  46  may additionally determine faults in the refrigeration system  12  along with determining the subcooling temperature and the charge condition. For example, the system controller  46  may determine a temperature difference (TD) between the SCT and the OAT (TD=SCT−OAT). The TD increases with an overcharge condition and decreases with an undercharge condition. The system controller  46  may further determine an approach temperature (AT) by subtracting the OAT from the LLT (AT=LLT−OAT). The AT decreases with an overcharge condition and increases with an undercharge condition. 
     Based on the foregoing, the system controller  46  is able to determine a refrigerant charge level and/or a fault by analyzing the AT, the TD and the SC without requiring additional temperature sensors (as illustrated in  FIG. 1 ). Further, because the TD is equivalent to the SC plus the AT (TD=SC+AT), the percent split or ratio between the SC and the AT (making up the TD) is a good indicator of which fault is occurring. 
     For overcharge conditions, the TD is high, but the AT is small, thus an SC/TD ratio is greater than approximately ninety percent (90%). For undercharge conditions, the TD is low and the SC is low, thus an AT/TD ratio is greater than approximately ninety percent (90%). Accordingly, the controller  46  may differentiate between other faults as well, as described in detail below. 
     With particular reference to  FIG. 9 , a bar graph detailing different refrigerant charge conditions and other faults for the refrigeration system  12  is provided. Each bar in the graph illustrates the values and/or the relationship among TD, SC, and/or AT for different conditions. For example, the normal charge condition may be declared by the system controller  46  when the following conditions are true: AT≅5° F., SC≅15° F., and TD≅AT+SC≅20° F. 
     When diagnosing faults in the system, the system controller  46  may perform additional calculations to assist in the diagnosis. For example, the system controller  46  may utilize other data that signifies a particular operating condition to allow the controller  46  to differentiate amongst faults having similar characteristics. For example, the TDs for a one hundred thirty percent (130%) charge (overcharge) condition and a low condenser air flow condition (dirty coil) are both high (for example only, 35° F.). In order to differentiate between these two faults, the system controller  46  may determine a ratio of SC to TD. The controller  46  may declare an overcharge condition when SC/TD is greater than approximately ninety percent (90%), and may declare a low condenser air flow fault (e.g. blocked or dirty condenser coil or condenser fan fault) when SC/TD is less than approximately ninety percent (90%). 
     The TDs for both a seventy-five percent (75%) charge (undercharge) condition and a thermal expansion valve (TXV) flow control restriction are low (for example only, 14° F. and 13° F., respectively). In order to differentiate between these two faults, the system controller  46  may determine a ratio of AT to TD. The undercharge condition may be declared when the ratio of AT/TD is greater than approximately ninety percent (90%) and the TXV fault may be declared when the ratio of AT/TD is less than approximately ten percent (10%). 
     As previously described, the coil temperature sensors  58 ,  62  may be used to determine the charge condition of the refrigeration system  12 . This information may be useful when installing a new refrigeration system  12  or, alternatively, when monitoring or charging an existing system  12  following maintenance. In one configuration, the temperature sensors  58 ,  62  may be used in conjunction with an algorithm that utilizes information from the temperature sensors  58 ,  62  to aid in providing the refrigeration system  12  with the proper amount of refrigerant. 
     The algorithm may be performed by a computer such as, for example, a hand-held device or a laptop computer ( FIG. 8 ). The computing device may prompt the installer to first select a line length of a refrigeration line set and a diameter of the line set at  140 . For example, the line length and diameter may respectively be forty feet and three-eighths of an inch (40 1/32 ft). The installer may power on the system and wait approximately fifteen minutes or until the system controller  46  indicates that the system is stable for charging at  142 . Because the factory charge is intended for only fifteen feet (15 ft) of refrigeration line, this particular unit may be undercharged, as described at  144 . Thus, both the temperature reading from the first coil temperature sensor  58  and the temperature reading from the second coil temperature sensor  62  are valid SCTs in this situation. The controller  46  may calculate the SC using the formula SC=SCT−LLT and confirm whether approximately two degrees Fahrenheit is less than the SC and whether the SC is less than a target SC (2° F.&lt;SC&lt;SCtarget) at  146 , where the target SC is approximately ten degrees Fahrenheit (10° F.). If the target SC is provided from original equipment manufacturer data, the system controller  46  will use this as the target SC instead. 
     The system controller  46  may calculate and display an amount of charge (X) to be added at  148 . The system controller may prompt the installer to add X charge to the system at  150  (if X is large, the addition may be performed in a plurality of increments). The system controller  46  may check for system stabilization and may display the SC versus the target SC on the computing device at  152 . When the SC is approximately equal to the target SC, the system controller  46  may indicate that the charge is complete at  154 . If the installer adds more charge than requested by the system controller  46 , the system controller  46  may determine an overcharge condition and may prompt the installer to recover and start the charge process again at  156 . 
     The charge-verification system  10  and method  100  may also be applied to a split heat pump operating in a heating mode if both the first coil temperature sensor  58  and the second coil temperature sensor  62  are positioned on the indoor coil of the heat pump system. The SCT determined may be used to calculate a Discharge Superheat (DSH). Further, the charge-verification system  10  and method  100  are intended for both initial installation as well as on-going monitoring and maintenance service of the refrigeration system  12 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Those skilled in the art may now appreciate from the foregoing that the broad teachings of the present disclosure may be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.