Abstract:
A system includes a compressor receiving fluid from a low-pressure side of a circuit and outputting fluid to a high-pressure side of the circuit. The system also includes a motor drivingly connected to the compressor, at least one high-side sensor operable to measure fluid properties of the high-pressure side of the circuit, at least one current sensor operable to monitor a current drawn by the motor, and processing circuitry receiving fluid property and current information from the at least one high-side sensor and the at least one current sensor and processing the information to determine a system operating condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/990,566 filed on Nov. 21, 2001, now U.S. Pat. No. 6,758,050 which is a continuation-in-part application of U.S. patent application Ser. No. 09/818,271 filed on Mar. 27, 2001 (now U.S. Pat. No. 6,615,594). The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a diagnostic system for a refrigeration or air-conditioning system. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     A class of machines exists in the art generally known as scroll machines which are used for the displacement of various types of fluid. These scroll machines can be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present invention are applicable to any of these machines. For purposes of illustration, however, the disclosed embodiment is in the form of a hermetic refrigerant scroll compressor used within a refrigeration or air conditioning system. 
     Scroll compressors are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes. While the diagnostic system of the present invention will be described in conjunction with a scroll compressor, it is to be understood that the diagnostic system of the present invention can be used with other types of compressors also. 
     Traditionally, when an air conditioning or refrigeration system is not performing as designed, a technician is called to the site for trouble shooting the problem. The technician performs a series of checks that assists in isolating the problem with the system. One of the causes of the system&#39;s problem could be the compressor used in the system. A faulty compressor exhibits some operational patterns that could be used to detect the fact that the compressor is faulty. Unfortunately, many other causes for system problems can be attributed to other components in the system and these other causes can also affect the performance of the compressor and its operational pattern. It is possible to analyze the system&#39;s problems and operational patterns and determine that the compressor is faulty when in fact the problem lies elsewhere and the compressor is not the problem. This confusion of causes usually results in the replacement of a good compressor. This error in diagnosis is costly since the compressor is generally the most expensive component in the system. Further aggravating the problem is that the root cause for the system&#39;s problem has not been solved and the problem recurs in time. Any tool which can help avoid the misdiagnosing of the system&#39;s problem as described above would prove both useful and cost effective. The present invention discloses a device that increases the accuracy of the problem diagnosis for an air conditioning or refrigeration system. 
     A large part of the compressors used in air conditioning and refrigeration systems have built-in protection devices called “internal line break protectors”. These protectors are thermally sensitive devices which are wired in electrical series with the motor. The protectors react thermally to the line current drawn by the motor and also other temperatures within the compressor including but not limited to discharge gas temperature, suction gas temperature or temperature of a particular component in the compressor. When one of these temperatures exceeds a designed threshold, the protector will open the electrical connection to the motor. This shuts down the motor operating the compressor which in turn shuts down the compressor and prevents it from operating in regions that would lead to its failure. After a period of time, when the temperatures have fallen to safe levels, the protector automatically resets itself and the compressor operates again. The temperatures that the protector is reacting to are a result of the operation of the compressor and the entire refrigeration or air-conditioning system. Either the operation of the compressor or the operation of the entire system can influence the temperatures sensed by these protectors. The significant aspect of the protection system is that some categories of faults repeatedly trip the protector with very short compressor ON time and other categories of faults trip the protector less frequently thus providing relatively longer compressor ON times. For example, a compressor with seized bearings would trip the protector within about twenty seconds or less of ON time. On the other hand, a system that has a very low refrigerant charge will trip the protector after typically more than ninety minutes of ON time. An analysis of the trip frequency, trip reset times and compressor ON times will provide valuable clues in identifying the cause of the system&#39;s problems. 
     The present invention provides a device which is based on this principle. The device of the present invention continuously records the status of the protector (open or closed) as a function of time and then it analyzes this status information to determine a faulty situation. The device goes further and isolates the fault to either the compressor or to the rest of the system. Once the fault has been isolated, the device will activate a visual indicator (light) and it will also send an electrical signal to any intelligent device (controller, computer, etc.) advising about the situation. The technician, on arriving at the scene, then has a clear indication that the problem is most likely in the system components other than the compressor or the problem is most likely in the compressor. He can then focus his further trouble shooting to the identified area. The device thus avoids the previously described situation of a confused diagnosis and the potential of mistakenly replacing a good compressor. 
     In addition to the status of the protector, additional information can be gathered by sensors that monitor other operating characteristics of the refrigeration system such as supply voltage and outdoor ambient temperature. This additional information can then be used to further diagnose the problems associated with the refrigeration or air-conditioning system. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a vertical cross section of a hermetic scroll compressor incorporating the unique compressor diagnostic system in accordance with the present invention; 
         FIG. 2  is a schematic representation of the diagnostic system for a single phase motor for the compressor in accordance with the present invention; 
         FIG. 3  is a schematic representation of a diagnostic system for a three phase motor for the compressor in accordance with another embodiment of the present invention; 
         FIG. 4  is a flow diagram of the diagnostic system for the single phase motor for the compressor in accordance with the present invention; 
         FIG. 5  is a flow diagram of the diagnostic system for the three phase motor for the compressor in accordance with the present invention; 
         FIG. 6  is a flow diagram which is followed when diagnosing a compressor system; 
         FIG. 7  is a schematic view of a typical refrigeration system utilizing the compressor and diagnostic system in accordance with the present invention; 
         FIG. 8  is a perspective view of a contactor integrated with the diagnostic system&#39;s circuitry in accordance with another embodiment of the present invention; 
         FIG. 9  is a schematic view illustrating the circuitry of the contactor illustrated in  FIG. 8 ; 
         FIG. 10  is a schematic view of a compressor plug which illustrates the diagnostic system&#39;s circuitry in accordance with another embodiment of the present invention; 
         FIG. 11  is a flow diagram of a diagnostic system for the compressor in accordance with another embodiment of the present invention; 
         FIG. 12  is a chart indicating the possible system faults based upon ON time before trips; 
         FIG. 13  is a graph showing electrical current versus the temperature of the condenser; 
         FIG. 14  is a graph showing percent run time versus outdoor ambient temperature; and 
         FIG. 15  is a schematic illustration of a diagnostic system in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIG. 1  a scroll compressor incorporating the unique compressor diagnostic system in accordance with the present invention and which is designated generally by the reference numeral  10 . While compressor  10  is being illustrated as a scroll compressor in conjunction with a refrigeration or air conditioning system, it is within the scope of the present invention to utilize other types of compressors in the refrigeration or air conditioning system if desired as well as having any of the compressor designs being in conjunction with other types of systems. 
     Scroll compressor  10  comprises a generally cylindrical hermetic shell  12  having welded at the upper end thereof a cap  14  and at the lower end thereof a base  16  having a plurality of mounting feet (not shown) integrally formed therewith. Cap  14  is provided with a refrigerant discharge fitting  18  which may have the usual discharge valve therein. A transversely extending partition  20  is affixed to shell  12  by being welded about is periphery at the same point that cap  14  is welded to shell  12 . A compressor mounting frame  22  is press fit within shell  12  and it is supported by the end of base  16 . Base  16  is slightly smaller in diameter than shell  12  such that base  16  is received within shell  12  and welded about its periphery as shown in  FIG. 1 . 
     Major elements of compressor  10  that are affixed to frame  22  include a two-piece main bearing housing assembly  24 , a lower bearing housing  26  and a motor stator  28 . A drive shaft or crankshaft  30  having an eccentric crank pin  32  at the upper end thereof is rotatably journaled in a bearing  34  secured within main bearing housing assembly  24  and a second bearing  36  secured within lower bearing housing  26 . Crankshaft  30  has at the lower end thereof a relatively large diameter concentric bore  38  which communicates with a radially outwardly positioned smaller diameter bore  40  extending upwardly therefrom to the top of crankshaft  30 . The lower portion of the interior of shell  12  defines an oil sump  44  which is filled with lubricating oil to a level slightly above the lower end of a rotor, and bore  38  acts as a pump to pump lubricating fluid up crankshaft  30  and into bore  40  and ultimately to all of the various portions of compressor  10  which require lubrication. 
     Crankshaft  30  is rotatably driven by an electric motor which includes stator  28 , windings  46  passing therethrough and a rotor  48  press fitted into crankshaft  30 . An upper counterweight  50  is secured to crankshaft  30  and a lower counterweight  52  is secured to rotor  48 . A temperature protector  54 , of the usual type, is provided in close proximity to motor windings  46 . Temperature protector  54  will de-energize the motor if thermal protector  54  exceeds its normal temperature range. Temperature protector  54  can be heated by motor windings  46 , suction gas within a suction chamber  56  and/or discharge gas within a discharge chamber  58  which is released into suction chamber  56 . Both suction chamber  56  and discharge chamber  58  are defined by shell  12 , cap  14 , base  16  and partition  22  as shown in  FIG. 1 . 
     The upper surface of two-piece main bearing housing assembly  24  is provided with a flat thrust bearing surface on which is disposed an orbiting scroll member  60  having the usual spiral vane or wrap  62  extending upward from an end plate  64 . Projecting downwardly from the lower surface of end plate  64  of orbiting scroll member  60  is a cylindrical hub  66  having a journal bearing therein and which is rotatably disposed a drive bushing  68  having an inner bore in which crank pin  32  is drivingly disposed. Crank pin  32  has a flat on one surface which drivingly engages a flat surface formed in a portion of the inner bore of drive bushing  68  to provide a radially compliant driving arrangement, such as shown in Assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is hereby incorporated herein by reference. An Oldham coupling  70  is also provided positioned between orbiting scroll member  60  and two-piece bearing housing assembly  24 . Oldham coupling  70  is keyed to orbiting scroll member  60  and to a non-orbiting scroll member  72  to prevent rotational movement of orbiting scroll member  60 . 
     Non-orbiting scroll member  72  is also provided with a wrap  74  extending downwardly from an end plate  76  which is positioned in meshing engagement with wrap  62  of orbiting scroll member  60 . Non-orbiting scroll member  72  has a centrally disposed discharge passage  78  which communicates with an upwardly open recess  80  which is in turn in communication with discharge chamber  58 . An annular recess  82  is also formed in non-orbiting scroll member  72  within which is disposed a floating seal assembly  84 . 
     Recesses  80  and  82  and floating seal assembly  84  cooperate to define axial pressure biasing chambers which receive pressurized fluid being compressed by wraps  62  and  74  so as to exert an axial biasing force on non-orbiting scroll member  72  to thereby urge the tips of respective wraps  62  and  74  into sealing engagement with the opposed end surfaces of end plates  76  and  64 , respectively. Floating seal assembly is preferably of the type described in greater detail in Assignee&#39;s U.S. Pat. No. 5,156,639, the disclosure of which is hereby incorporated herein by reference. Non-orbiting scroll member  72  is designed to be mounted for limited axial movement with respect to two-piece main bearing housing assembly  24  in a suitable manner such as disclosed in the aforementioned U.S. Pat. No. 4,877,382 or Assignee&#39;s U.S. Pat. No. 5,102,316, the disclosure of which is hereby incorporated herein by reference. 
     Compressor  10  is powered by electricity which is provided to the electric motor within shell  12  through a molded electric plug  90 . 
     Referring now to  FIGS. 1 through 3 , the present invention is directed to a unique compressor diagnostic system  100 . Diagnostic system  100  comprises one or more current sensing devices  102  and the associated logic circuitry  104 . Current sensing devices  102  are mounted in a housing  106  mounted externally to shell  12 . Logic circuitry  104  can be mounted in housing  106  or it can be located in a convenient position with respect to compressor  10  as shown in phantom in  FIG. 2 . Optionally, the sensing device and circuitry can be integrated into a special contactor, a special wiring harness or into a molded plug utilized for some compressor designs. 
     Current sensing devices  102  sense the current in the power supply wires powering compressor  10 .  FIG. 2  illustrates two current sensing devices  102  in conjunction with a single-phase motor. One of the current sensing devices  102  is associated with the main windings for the compressor motor and the other current sensing device  102  is associated with the auxiliary windings for the compressor motor.  FIG. 3  also illustrates two current sensing devices  102  in conjunction with a three phase motor. Each current sensing device  102  is associated with one of the phases of the three phase power supply. While  FIG. 3  illustrates two current sensing devices sensing current in two phases of the three phase power supply, it is within the scope of the present invention to include a third current sensor  102  to sense the current in the third phase of the three phase power supply as shown in phantom in  FIG. 3  if desired. These current signals represent an indication of the status of protector  54  (open or closed). While current sensing devices  102  sense the status of protector  54  utilizing the current in the power supply wires, it is also possible to sense the status of protector  54  by sensing the presence or absence of voltage on the motor side of protector  54 . The inventors of the present invention consider this to be a less desirable but effective approach in some cases because it requires an additional hermetic feed-through pin extending through shell  12 . The signals received from current sensing devices  102  are combined in logic circuitry  104  with the demand signal for compressor  10 . The demand signal for compressor  10  is acquired by sensing the presence of supply voltage or by having a system controller (not shown) supply a discrete signal representing the demand. The demand signal and the signal received by-logic circuitry  104  are processed by logic circuitry  104  to derive the information about the trip frequency of protector  54  and the average ON time and OFF time of compressor  10 . Logic circuitry  104  analyses the combination of current signals, the demand signal and the derived protector trip frequencies to determine if a fault condition exists. Logic circuitry also has the unique capability of identifying a specific cause based on some faults. This information is provided to the service people using a green LED light  110  and a yellow LED light  112 . Green LED light  110  is utilized to indicate that there is currently no fault condition and that the system is functioning normally. 
     Yellow LED light  112  is utilized to indicate the presence of a fault. When yellow LED light  112  is turned ON, green LED light  110  is turned OFF. Thus, yellow LED light  112  is utilized to visually communicate that there is a fault as well as indicating the type of fault that is present. This communication is accomplished by turning yellow LED light  112  ON and then OFF for a specific duration and sequence to indicate both that there is a fault and to identify what the fault is. For example, turning light  112  ON for one second and turning it OFF for nineteen seconds and repeating this sequence every twenty seconds will create the effect of a blinking light that blinks ON once every twenty seconds. This sequence corresponds to a type of fault that is coded as a type  1  fault. If light  112  is blinked ON twice for one second during the twenty second window, it is an indication that a fault that is coded as a type  2  is present. This sequence continues to indicate a type  3 , a type  4  and so on with the type of fault being indicated by the number of blinks of light  112 . This scheme of the blinking of light  112  for a specific number of times is employed to visually communicate to the technician the various types of faults detected by logic circuitry  104 . While the present invention utilizes blinking light  112  to convey the fault codes, it is within the scope of the present invention to utilize a plurality of lights to increase the effectiveness of conveying a large number of fault codes if desired. In addition, other methods of providing the default code, including providing a coded voltage output that can be interfaced with other electronic devices, can also be employed. 
     In addition to visually communicating the specific fault code using light  112 , logic circuitry  104  also outputs a coded sequence of electrical pulses to other intelligent controllers that may exist in the system. These coded pulses represent the type of fault that has been detected by diagnostic system  100 . The types of faults which can be detected by logic circuitry  104  include, but are not limited to:
     1. Protector has “tripped”.   2. The auxiliary winding of a single phase motor has no power or is open or has a faulty run capacitor.   3. The main winding of a single phase motor has no power or that the winding is open.   4. The main circuit breaker has contacts that have welded shut.   5. One of the phases in a 3 phase circuit is missing.   6. The phase sequence in a 3 phase system is reversed.   7. The supply voltage is very low.   8. The rotor inside the compressor has seized.   9. The protector is tripping due to system high pressure side refrigeration circuit problems.   10. The protector is tripping due to system lower pressure side refrigeration circuit problems.   11. The motor windings are open or the internal line break protector is faulty.   12. The supply voltage to the compressor is low.   

     As a variation to the above, as shown in  FIG. 3 , diagnostic system  100  may only send the status of protector  54  to an intelligent device  116 . In this option, the parameters of trip frequencies, ON times and OFF times with the diagnosis information may be generated at intelligent device  116 . Intelligent device  116  can be a compressor controller associated with compressor  10 , it can be a system controller monitoring a plurality of compressors  10 , it can be a remotely located device or it can be any other device which is selected to monitor diagnostic system  100  of one or more compressors. 
       FIG. 4  represents a flow diagram for diagnostic system  100  in conjunction with a single phase compressor. The demand signal is provided to logic circuitry  104  from a device or a contactor  120  ( FIGS. 2 and 3 ) along with the current signal from sensing devices  102 . When the system is initially powered up, an initializing process is performed at  122  and, if successful, the system, as shown by arrow  124 , goes to a normal OFF condition as shown at  126 . When sitting at the normal OFF condition  126 , if a demand signal is provided to the system, the system moves as shown by arrow  128  to a normal run condition shown at  130 . Once the demand has been met, the system returns to the normal OFF condition  126  as shown by arrow  132 . 
     While sitting at the normal OFF condition  126 , if current in the main winding or current in the auxiliary winding is detected and there has been no demand signal, the system moves as shown by arrow  134  to a shorted contactor condition  136 . While indicating the shortened contactor condition  136 , if the demand is signaled, the system moves as shown by arrow  138  to the normal run condition  130 . The normal run condition  130  continues until the demand has been satisfied where the system moves as shown by arrow  132  back to the normal OFF condition  126  which may again move to the shortened contactor condition  136  depending on whether or not current is sensed in the main or auxiliary windings. 
     While operating in the normal run condition  130 , one of three paths other than returning to the normal OFF condition  126  can be followed. First, if the system senses demand and main winding current but does not sense auxiliary winding current, the system moves as shown by arrow  140  to an open auxiliary circuit condition  142 . From here, the system moves to a protector tripped condition  144  as shown by arrow  146  when both a main winding current and an auxiliary winding current are not sensed. Second, if the system senses demand and auxiliary winding current but does not sense main winding current, the system moves as shown by arrow  148  to an open main circuit condition  150 . From here, the system moves to the protector tripped condition  144  as shown by arrow  152  when both a main winding current and an auxiliary winding current are not sensed. Third, if the system senses demand and does not sense auxiliary winding current and main winding current, the system moves as shown by arrow  154  to the protector tripped condition  144 . 
     While operating in the protector tripped condition  144 , one of four paths can be followed. First, if main winding current or auxiliary winding current is sensed and the demand is satisfied, the system moves as shown by arrow  160  to the normal run condition  130 . Second, with the protector tripped, and the moving window average of the ON time of the system has been less than twelve seconds, the system moves as shown by arrow  162  to a multiple short run condition  164 . From the multiple short run condition, the system moves back to the protector tripped condition  144  as shown by arrow  166 . Third, with the protector tripped, and the moving window average of the ON time of the system has been greater than fifteen minutes, the system moves as shown by arrow  168  to a multiple long run condition  170 . The system moves back to the protector tripped condition  144  as shown by arrow  172 . Fourth, with the protector tripped, if the tripped time exceeds four hours, the system moves as shown by arrow  174  to a power loss or protector defective condition  176 . If, while the system is in the power loss or protector defective condition  176  and main winding current or auxiliary winding current is sensed, the system moves back to the protector tripped condition  144  as shown by arrow  178 . 
     When the system moves to the various positions shown in  FIG. 4 , the blinking of light  112  is dictated by the fault condition sensed. In the preferred embodiment, if a protector tripped condition is sensed at  154  because demand is present but current is missing, light  112  blinks once. If compressor  10  is seized or there is a low supply voltage problem such as indicated by arrow  162  because the average ON time during the last five trips was less than twelve seconds, light  112  blinks twice. If the motor windings are open, the protector is faulty or the contactor is faulty as indicated by arrow  174  because the OFF time is greater than four hours, light  112  blinks three times. If the auxiliary windings are open or there is a faulty run capacitor as indicated by arrow  140 , light  112  blinks four times. If the main winding is open as indicated by arrow  148 , light  112  blinks five times. If the contactor is welded as indicated by arrow  134  because current is sensed but there is no demand, light  112  blinks six times. Finally, if there are repeated protector trips due to other system problems as indicated by arrow  168  because the average ON time during the last five trips was less than fifteen minutes, light  112  blinks seven times. 
       FIG. 5  represents a flow diagram for diagnostic system  100  in conjunction with a three phase compressor. The demand signal is provided to logic circuitry  104  from contactor  120  ( FIGS. 2 and 3 ) along with the current signal from sensing devices  102 . When the system is initially powered up, an initializing process is performed at  122  and, if successful, the system, as shown by arrow  124 , goes to a normal OFF condition as shown at  126 . When sitting at the normal OFF condition  126 , if a demand signal is provided to the system, the system moves as shown by arrow  128  to a normal run condition shown at  130 . Once the demand has been met, the system returns to the normal OFF condition  126  as shown by arrow  132 . 
     While sitting at the normal OFF condition  126 , if current in one of the three phases or current in a second of the three phases is detected and there has been no demand signal the system moves as shown by arrow  234  to a shorted contactor condition  136 . While indicating the shortened contactor condition  136 , if the demand is signaled, the system moves as shown by arrow  238  to the normal run condition  130 . The normal run condition  130  continues until the demand has been satisfied where the system moves as shown by arrow  132  back to the normal OFF condition  126  which may again move to the shortened contactor condition  136  depending on whether or not current is sensed in the main or auxiliary windings. 
     While operating in the normal run condition  130 , one of three paths other than returning to the normal OFF condition  126  can be followed. First, if the system senses demand and eleven milliseconds is less than the zero crossing time difference between the first and second phases of the three phase power supply or this time difference is less than fourteen milliseconds, the system moves as shown by arrow  240  to a phase sequence reversed condition  242 . From here, the system moves to a protector tripped condition  144  as shown by arrow  246  when both a first phase current or a second phase current is not sensed. Second, if the system senses demand and sixteen milliseconds is less than the zero crossing time difference between the first and second phases or this time difference is less than twenty-one milliseconds, the system moves as shown by arrow  248  to a phase missing condition  250 . From here, the system moves to the protector tripped condition  144  as shown by arrow  252  when both a first phase current and a second phase current are not sensed. Third, if the system senses demand and does not sense first phase current and second phase current, the system moves as shown by arrow  254  to the protector tripped condition  144 . 
     While operating in the protector tripped condition  144 , one of four paths can be followed. First, if first phase current or second phase current is sensed and the demand is satisfied, the system moves as shown by arrow  260  to the normal run condition  130 . Second, with the protector tripped, and the moving window average of the ON time of the system has been less than twelve seconds, the system moves as shown by arrow  162  to a multiple short run condition  164 . From the multiple short run condition, the system moves back to the protector tripped condition  144  as shown by arrow  166 . Third, with the protector tripped, and the moving window average of the ON time of the system has been greater than fifteen minutes, the system moves as shown by arrow  168  to a multiple long run condition  170 . The system moves back to the protector tripped condition  144  as shown by arrow  172 . Fourth, with the protector tripped, if the tripped time exceeds four hours, the system moves as shown by arrow  174  to a power loss or protector defective condition  176 . If, while the system is in the power loss or protector defective condition  176  and first phase current or second phase current is sensed, the system moves back to the protector tripped condition  144  as shown by arrow  278 . 
     When the system moves to the various positions shown in  FIG. 5 , the blinking of light  112  is dictated by the fault condition sensed. In the preferred embodiment, if a protector tripped condition is sensed at  254  because demand is present but current is missing, light  112  blinks once. If compressor  10  is seized or there is a low supply voltage problem such as indicated by arrow  162  because the average ON time during the last five trips was less than twelve seconds, light  112  blinks twice. If the motor windings are open, the protector is faulty or the contactor is faulty as indicated by arrow  174  because the OFF time is greater than four hours, light  112  blinks three times. If the contactor is welded as indicated by arrow  234  because current is sensed but there is no demand, light  112  blinks four times. If there are repeated protector trips due to other system problems as indicated by arrow  168  because the average ON time during the last five trips was less than fifteen minutes, light  112  blinks five times. If the power supply phases are reversed as indicated by arrow  240  because the zero crossing time difference is between eleven and fourteen milliseconds, light  112  blinks six times. Finally, if there is a phase missing in the three phase power supply as indicated by arrow  248  because the zero crossing time difference is between sixteen and twenty-one milliseconds, light  112  blinks seven times. 
     While the above technique has been described as monitoring the moving window averages for compressor  10 , it is within the scope of the present invention to have logic circuitry  104  utilize a real time or the instantaneous conditions for compressor  10 . For instance, in looking at arrows  162  or  168 , rather than looking at the moving window average, logic circuitry  104  could look at the previous run time for compressor  10 . 
       FIG. 6  represents a flow diagram which is followed when diagnosing a system problem. At step  300 , the technician determines if there is a problem by checking the LEDs at step  302 . If green LED  110  is lit, the indication at  304  is that compressor  10  is functioning normally and the problem is with other components. If yellow LED light  112  is blinking, the technician counts the number of blinks at  306 . Based upon the number of blinks of light  112  the determination of the failure type is made at  308 . The fault is corrected and the system is recycled and started at  310 . The system returns to step  300  which again will indicate any faults with compressor  10 . 
     Thus, diagnostic system  100  provides the technician who arrives at the scene with a clear indication of most likely where the problem with the system is present. The technician can then direct his attention to the most likely cause of the problem and possibly avoid the replacement of a good compressor. 
       FIG. 7  illustrates a typical refrigeration system  320 . Refrigeration system  320  includes compressor  10  in communication with a condensor  322  which is in communication with an expansion device  324  which is in communication with an evaporator  326  which is in communication with compressor  10 . Refrigerant tubing  328  connects the various components as shown in  FIG. 7 . 
     Referring now to  FIG. 8 , a contactor  120  is illustrated which incorporates diagnostic system  100  in the form of current sensors  102 , logic circuitry  104 , green LED light  110  and yellow light  112 . Contactor  120  is designed to receive information from various system controls such as a system thermostat  350  ( FIGS. 2 and 3 ), a group of system safeties  352  ( FIGS. 2 and 3 ) and/or other sensors incorporated into the system and based upon three inputs provide power to compressor  10 . 
     Contactor  120  includes a set of power-in connectors  354 , a set of power-out connectors  356 , a set of contactor coil connectors  358 , light  110  and light  112 . The internal schematic for contactor  120  is shown in  FIG. 9 . A power supply  360  receives power from connectors  354 , converts the input power as needed and then supplies the required power to input circuitry  362 , processing circuitry  364  and output circuitry  366 , which collectively form logic circuitry  104 . 
     Input circuitry  362  receives the input from current sensors  102  and the demand signal in order to diagnose the health of compressor  10 . The information received by input circuitry  362  is directed to processing circuitry  364  which analyses the information provided and then provides information to output circuitry  366  to operate compressor  10  and/or activate LED lights  110  and  112 . The incorporation of logic circuitry  104  into contactor  120  simplifies the system due to the fact that both the line power and the demand signal are already provided to contactor  120 . The function and operation of diagnostic system  100  incorporated into contactor  120  is the same as described above for housing  106 . 
     Referring now to  FIG. 10 , molded plug  90  is illustrated incorporating diagnostic system  100  in the form of current sensors  102 , logic circuitry  104 , light  110  and light  112 . In some applications, incorporation of diagnostic system  100  into molded plug  90  offers some distinct advantages. When diagnostic system  100  is incorporated into molded plug  90 , power is provided through connectors  354  and must also be provided to diagnostic system from the input power or it can be provided separately through connector  370 . In addition, the demand signal must also be provided to plug  90  and this can be done through connectors  372 . The function and operation of diagnostic system  100  incorporated into molded plug  90  is the same as described above for housing  106 . Communication from plug  90  is accomplished through connection  374 . 
       FIGS. 4 and 5  illustrate flow diagrams for diagnostic system  100 . While operating in the protector tripped condition  144 , different paths are followed depending upon the moving window average of the ON time or the previous cycle ON time. These various paths help to determine what type of fault is present. 
     This concept can be expanded by making additional assumptions based upon the compressor ON time between overload trips. The compressor ON time duration prior to the overload trip can be expanded to be useful in diagnosing whether the fault is likely located on the high-side (condenser) or on the low-side (evaporator) of the refrigeration or air conditioning system. This added information would help the technician speed up his search for the fault.  FIG. 11  illustrates the flow diagram for a diagnostic system  100 . While  FIG. 11  illustrates a diagnostic system for a single phase motor, the diagnostic system illustrated in  FIG. 11  and described below can be utilized with a three phase motor, if desired. 
     Using this approach, there are four major system faults as shown in  FIG. 12  that can be identified based on the ON time and/or OFF time. First, a “locked rotor” (LR Trip) condition typically results from a compressor mechanical lock-out or a hard start problem. This results in the shortest trip time usually within twenty seconds or less. This is illustrated in  FIG. 11  by arrow  162 ′ which leads to a locked rotor condition  164 : from the locked rotor condition  164 ; the system moves back to the protector tripped condition  144  as shown by arrow  166 ′. Second, a “short cycling” condition is typically due to cut-in and cut-out of either the high-side or the low-side safety pressure switches. Both the ON time and OFF time during short cycling are typically in the order of two minutes or less. This is illustrated in  FIG. 11  by arrow  162 ″ which leads to a short cycling run condition  164 ″. From the short cycling run condition  164 ″, the system moves back to the protector tripped condition  144  as shown by arrow  166 ″. Third, a “normal overload trip” (protector trip) condition is the one expected to occur most often imposing a max-load condition on the compressor due to system faults such as a blocked or failed condenser fan. The ON time between trips can be anywhere from four to ninety minutes depending on the severity of the faults. This is illustrated in  FIG. 11  by arrow  168 ′ which leads to a normal overload trip condition  170 ′. From the normal overload trip condition  170 ′, the system moves back to the protector tripped condition  144  as shown by arrow  172 ′. As shown in  FIG. 12 , the normal overload trip can be broken down into two separate areas of the temperature if condenser  322  (Tc) is known. Fourth, a “high run time” fault condition results in very long run times typically greater than ninety minutes. A normal fifty per-cent run-time thermostat cycling based on a rate of three cycles per hour would produce an ON time of ten minutes. Thus, running more than ninety minutes is typically a fault. This is illustrated in  FIG. 11  by arrow  174 ′ which leads to a loss of charge fault  176 ′. From the loss of charge fault  176 ′, the system moves back to the protector tripped condition  144  as shown by arrow  178 ′. Diagnostic system  100 ′ can replace diagnostic system  100  shown in  FIGS. 4 and 5  or diagnostic system  101 ′ can run concurrently with these other two diagnostic systems. 
     Additional information can be obtained using additional sensors. By adding key sensors, the diagnostic systems described above can extend into a major capability that can clearly distinguish between a compressor fault and a system fault on any set or conditions. 
     Specifically, for a given voltage and power supply type, the running current for compressor  10  is mainly a prescribed function of its discharge pressure and its suction pressure as represented by typical published performance tables or equations. Typically, for most scroll compressors, the compressor current varies mainly with the discharge pressure and it is fairly insensitive to suction pressure. When a mechanical failure occurs inside scroll compressors, its current draw will increase significantly at the same discharge pressure. Therefore, by sensing current with current sensing devices  102  and by sensing discharge pressure using a sensor  330  as shown in  FIG. 7 , most faults inside compressor  10  can be detected. For a given power supply, a change in voltage can affect its current. However, these voltage changes are usually intermittent and not permanent, while a fault is typically permanent and irreversible. This difference can be distinguished by detecting the current with current sensing devices  102  and by detecting the discharge pressure with sensor  330  for several repetitive cycles. 
     Typically, discharge pressure sensor  330  is a fairly expensive component, especially for residential system implementation. A low-cost alternative is to use a temperature sensor CR thermistor  332  as shown in  FIG. 7  mounted at the mid-point of condenser  322  on one of the tube hairpin or return bends. This temperature sensing is fairly well known as it is used with demand-type defrost control for residential heat pumps.  FIG. 13  illustrates a typical relationship between compressor current and condensing temperature. A generic equation or table for this relationship can be pre-programmed into diagnostic systems  100  or  100 ′. Then by measuring two or three coordinate points during the initial twenty-four hours of operation after the first clean installation, the curve can then be derived and calibrated to the system for use as a no-fault reference. 
     In addition to current sensing devices  102 , pressure sensor  330  or temperature sensor  332 , an outdoor ambient temperature sensor  334  as shown in  FIGS. 2 and 3  may be added. The addition of sensor  334  is mainly for detecting compressor faults by leveraging the data from sensors  102  and  330  or  332  with the data from sensor  334 . Since both temperature sensor  332  and temperature sensor  334  are typically used with demand-type defrost controls in residential heat pumps, this concept is fairly attractive because the technicians are already familiar with these sensors and the added cost is only incremental. 
     The combination of condensing temperature and condenser delta T (condensing temperature minus ambient temperature) now provides more powerful diagnostic capability of system faults as illustrated below including heat pumps in the heating mode because the delta T becomes evaporation temperature minus ambient temperature. In the chart below in the cooling mode, the delta T represents condenser delta T and in the heating mode, the delta T represents evaporator delta T. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Cooling mode 
                 Heating mode 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Outdoor fan blocked/failed 
                 Overload trip 
                   
               
               
                 Or Overcharge (High side) 
                 High delta T 
                 Low delta T 
               
               
                   
                 High Tcond 
               
               
                   
                 High current 
               
               
                 Indoor blower blocked/failed 
                 Low delta T 
                 Overload trip 
               
               
                 Or Loss of Charge (Low side) 
                 Low delta T 
                 Low delta T 
               
               
                   
                 Long run time 
                 Long run time 
               
               
                 Defrost initiation 
                 — 
                 High delta T 
               
               
                 Compressor Fault 
                 Current vs. Tcond 
                 — 
               
               
                 Capacity loss 
                 % run time 
                 % run time 
               
               
                   
               
             
          
         
       
     
     Finally, it is now possible to diagnose loss of capacity with the addition of outdoor ambient sensor  334  using percent run time as shown in  FIG. 14 . Predicting compressor energy use is also now possible because current, voltage and run time are known. The energy usage over time can be monitored and reported. 
     Overall, the implementation of an electronic diagnostic tool is illustrated in  FIG. 15  with current sensing devices  102 , condenser temperature sensor  332  and outdoor ambient temperature sensor  334 . Since these sensors provide continuous monitoring of the system and not single switches, it is now possible to integrate safety protection capability into this control and eliminate the need for high and low pressure safety switches. 
     Additional diagnostic capabilities can be achieved by sensing the voltage in the power supply wires powering compressor  10 . As shown in  FIGS. 2 and 3  illustrate voltage sensors  402  incorporated for this purpose. Compressors with internal line breaks like temperature sensor  54  will “trip” if the supply voltage to compressor  10  falls below a specified value. This value is typically ten percent below the nominal voltage. Under this reduced voltage condition, the motor current will increase to a level that would generate enough heat to “trip” protector  54 . Hence, if the voltage is known when protector  54  trips, this low voltage condition can be flagged as a specific fault. The service technician can then concentrate on finding the cause of the low voltage condition. The voltage can be sensed by several methods. It may be directly sensed at the compressure terminals as shown with sensors  402  or at other points in the electrical circuit feeding compressor  10 . It may also be indirectly sensed by monitoring the control voltage of the system using a sensor  404  as shown in  FIGS. 2 and 3 . The control voltage is typically a low voltage circuit (24 VAC) and it is derived using a step down transformer (not shown). This control voltage would also change in direct proportion to the change in line voltage. Hence, monitoring the control voltage could provide an idea of the line voltage. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.