Compressor diagnostic system

FIELD OF THE INVENTION

The present invention relates to a diagnostic system for a compressor. More particularly, the present invention relates to a diagnostic system for a refrigeration or air-conditioning system which uses the compressors “trip” information to diagnose the problems associated with the 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'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'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's problem has not solved and the problem recurs in time. Any tool which can help avoid the misdiagnosing of the system'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 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 ten seconds of ON time. On the other hand, a system that has a very low refrigerant charge will trip the protector after tens of 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'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.

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 limited 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'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

; and

FIG. 10

is a schematic view of a compressor plug which illustrates the diagnostic system's circuitry in accordance with another embodiment of 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

. Thermal protector

54

will de-energize the motor if thermal protector

54

exceeds its normal temperature range. Thermal 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'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'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'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 a Digital Volt Meter, 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 refrigeration circuit problems.

10. The motor windings are open or the internal line break protector is faulty.

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 condenser

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

.

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.