Method of charging a refrigeration system and apparatus therefor
United States Patent Anderson et al.  
 l l METHOD OF CHARGING A REFRIGERATION SYSTEM AND APPARATUS THEREFOR [75) Inventors: Richard M. Anderson. Smyrna;  
 Robert W. Ramsey. Nashville. both of Tenn.  
 [73] Assignee: Heil-Quaker Corporation.  
 Lewishurg. Tenn.  
 [22 Filed: Jan. 2, 1974 [21] Appl. No.: 430,181  
 [52] U.S. Cl. 62/77; 62/149; 62/292 [51] Int. Cl. F25!) 45/00 [58] Field of Search 62/77. M). 292  
 [56] References Cited UNITED STATES PATENTS 2.ll55.78() 9/l936 Zwickl 62/149 2.499.170 2/1951) Shoemaken 62/292 3.785J63 l/l974 Wagner 62/292 Apr. 8, 1975 i571 ABSTRACT A method of charging a refrigeration system and apparatus therefor which automatically brings the system to a desired superheat condition. The apparatus ineludes structure defining an expansion chamber in heat transfer association with the suction line of the refrigeration system, structure for determining the temperature of the expansion chamber structure. structure for causing the sensed temperature to be that selectively of the suction line refrigerant and that of the saturating refrigerant vapor at the suction line pressure. The difference between these temperatures is compared to a preselected superheat condition and structure is provided responsive to the comparison determination to add an incremental quantity of the refrigerant to the system whereby a series of such temperature determinations and refrigerant additions to the system may be effected to bring the system to the desired superheat condition.  
 l9 Claims, 5 Drawing Figures PATENTEDAPR&#39; 81915 3 875 755 saw 1 of 2 PATENTEBAPR M5 3, 875.755  
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 STABILI- DRYING CHARGING ZATION VALVES COUNTER L5.  
 METHOD OF CHARGING A REFRIGERATION SYSTEM AND APPARATUS THEREFOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to refrigeration apparatus and in particular, to apparatus for charging refrigeration apparatus utilizing a vaporizable refrigerant fluid.  
 2. Description of the Prior Art In one form of conventional refrigeration system. an expandable refrigerant fluid is utilized to absorb heat in an evaporator wherein the fluid is converted from a liq uid to a gas. The gas is then compressed by a suitable compressor and liquefied by a suitable condenser to be returned to the evaporator for subsequent evaporation and recirculation in the system. When the liquid refrigerant vaporizes in the evaporator. it absorbs a quantity of heat known as the heat of vaporization. Additional heat absorption by the vaporized refrigerant in the evaporator causes the refrigerant vapor to increase in temperature above the temperature of vaporization. The increase in temperature is conventionally defined as superheat.  
 In conventional refrigeration apparatuses. such as air conditioners. it is desirable to prevent or limit the supcrheating of the vaporized refrigerant for optimum operation of the refrigeration system. conventionally. the regulation of the superheat is effected by regulating the rate of flow of refrigerant liquid into the evaporator.  
  At times. it is necessary to add refrigerant to the system such as because of leaks and the like. Recharging of the system may be effected by a number of conventional methods. such as disclosed in U.S. letters Pat. No. 3.303.663 of WV. Miller et al and U.S. Pat. No. 3.400.552 of R.A. Johnson et al. In Miller et al. a refrigeration system is shown wherein a charging valve is provided for introducing refrigerant into an undercharged refrigeration system controlled by the temperaturepressure relationship in the system. The control includes both a temperature-responsive control element and a pressure responsive control element to effect the desired operation of the charging valve. In Johnson et al. a charging device is shown having electrically controlled inlet and bleed valves controlled by first and second pressure and first and second temperature transducers.  
  Control of the superheat condition in such a refrigeration system is disclosed in U.S. letters Pat. No. 3,577,743 of Joseph N. Long. The Long patent control utilizes a plurality of temperature sensing devices which cooperate to determine a temperature differential between the liquid and gaseous phase refrigerant in the system for controlling the superheat condition.  
 SUMMARY OF THE INVENTION The present invention comprehends an improved charging apparatus for charging a refrigeration system with refrigerant fluid which is controlled by the superheat condition of the refrigeration system. The charging apparatus determines the difference between the superheat condition of the apparatus and that of a preselected desired superheat condition and causes the addition of an incremental quantity of refrigerant fluid to the system. Upon the addition of the incremental quantity to the system, the charging apparatus redetermines the temperature differential so as to again detei mine the difference between the operating superheat condition and the desired superheat condition. The steps of temperature determination and refrigerant fluid addition are repeated seriatim until the determined operating superheat condition of the refrigeration system is substantially equal to the desired preselected superheat condition.  
  To provide an improved charging operation. the amount of refrigerant fluid added in the incremental quantities is caused to vary as a direct function of the magnitude of the determined temperature differential. Thus. where the determined temperature differential is relatively great. a relatively large quantity of refrigerant fluid is admitted to the system. The subsequent determination of a resultant smaller superheat condition differential then causes the control to admit a subsequent smaller incremental quantity of the refrigerant fluid to the system. The superheat condition determinations and refrigerant increment additions are repeated seriatim. thusly. with gradually decreasing incremental quantities of refrigerant fluid being added to the system so as to provide a zeroing-in on the preselected superheat condition thereby cffectively avoiding overcharg ing of the system and eliminating the need for bleeding valves. etc.  
  The charging apparatus and method of the present invention permits the determination of the superheat condition without requiring an addition of refrigerant fluid so that if the superheat condition is substantially equal to the desired superheat condition. no fluid will be added.  
  The charging apparatus utilizes a single condition re sponsive element in the form of a thermistor which is in thermal transfer association with the suction line and which is disposed to be subjected to a sample of liquid refrigerant from the delivery line to the evaporator to provide a saturated vapor temperature at the suction line pressure.  
  The servicing of refrigeration spparatus may be facilitated by provision of the refrigeration system with an expansion chamber means and valve controlled means for delivering liquid refrigerant from the condenser means to the expansion chamber means which are pro vided with the refrigerant system so that the servicing technician need only connect the control circuit portion of the charging system to the refrigeration system in the recharging operation for controlling the delivery of refrigerant fluid from a portable supply to the refrigeration system.  
  Thus, the refrigeration charging apparatus and method of the present invention are extremely simple and economical while yet providing the highly desirable features discussed above.  
 BRIEF DESCRIPTION OF THE DRAWING Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawing wherein;  
  FIG. I is a schematic view of a refrigeration system provided with a charging apparatus embodying the invention;  
  FIG. 2 is a schematic diagram illustrating a portion of the circuit of the charging apparatus;  
  FIG. 3 is a schematic circuit diagram illustrating the electrical control circuitry of the charging apparatus;  
  FIG. 4 is a schematic diagram illustrating a modified form of superheat determining means; and  
  FIG. 5 is a schematic circuit diagram of the timers and logic of the control.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment of the invention as disclosed in FIGS. l3 of the drawing. a refrigerant charging apparatus generally designated is shown for providing refigerant fluid from a pressurized supply I] to an operating refrigeration apparatus 12. Apparatus 10 is arranged to charge refrigeration apparatus I2 with incremental quantities of refrigerant fluid from supply 11 until the superheat condition of the refigeration apparatus 12 becomes substantially equal to a desired preselected superheat condition.  
  More specifically, refrigeration apparatus 12 may in clude a conventional evaporator 13. Liquefied refrigerant is delivered to evaporator 13 from a conventional condenser [4 through a suitable flow restrictor I5 herein comprising a capillary tube. Condenser 14 may include a conventional motor fan 16 which withdraws heat from the refrigerant fluid to effect liquefication thereof in the condenser. The liquid refrigerant fluid vaporizes in evaporator 13 as the result of the thermal transfer association thereof with the medium to be cooled. In the illustrated embodiment, a motoroperated fan 17 may be provided for flowing air to be refrigerated in thermal transfer association with the evaporator 13. The vaporized refrigerant fluid passes through a suction conduit 18 back to a compressor 19 of the refrigeration system which compresses the vaporized gas before delivery thereof to the condenser I4. Thus. the refrigerant liquid delivered from condenser l4 comprises high pressure refrigerant liquid and a conduit 20 between the condenser I4 and evaporator 13 comprises a high pressure liquid supply conduit in the refrigeration system.  
  The present invention comprehends providing a connection 21 to the liquid supply conduit 20 for delivering a sample of the refrigerant liquid from conduit 20 through a transfer conduit 22 to the charging apparatus 10.  
  Charging apparatus 10 includes, in the embodiment of FIGS. 1-3, chamber means 23 defining an expansion chamber 24 in thermal transfer association with suction line 18. Disposed within chamber 24 is a temperature responsive device 25 herein comprising a negative temperature coefficient thermistor adapted to respond to the temperature of the chamber means to provide through suitable leads 26 a signal corresponding to the sensed temperature to a control 27. Thus, normally, the temperature sensed by control 27 is the suction line temperature. To determine the amount of superheat represented by the determined suction gas temperalate. a quantity of liquid refrigerant is sprayed onto thermistor 25 so that the thermistor is cooled by evaporation of the liquid refrigerant to the saturation temperature at the suction line pressure which may be indicated by a suitable gauge 28 connected to a transfer conduit 29 between the expansion chamber means 23 and the suction line 18. The difference between the temperature of the thermistor when it is sprayed with the refrigerant from conduit 20 and the temperature of the thermistor when it is allowed to warm to the suction line gas temperature represents the superheat condition temperature differential, which determination is made in control 27 from the two temperatures so sensed.  
  Control 27, in turn, controls a solenoid operated test valve 30 connected between conduit 22 and chamber 24. the valve 30 being electrically connected to control 27 by suitable leads 31. Control 27 further controls a second valve 32 connected in the delivery conduit 33 from refrigerant supply I 1. Valve 32 may be connected to control 27 by suitable leads 34.  
  Transfer conduit 22 may be provided with a manual shutoff valve 35 and pressure gauge 36. A capillary restrictor 37 may be connected between valve 30 and pressure chamber means 23. A manual shutoff valve 38 may be provided in delivery conduit 33 and a flow restrictor capillary 39 may be connected between valve 32 and transfer conduit 29. As the signals delivered to control 27 from thermistor 25 determine the difference between the suction gas temperature and the saturated refrigerant vapor temperature corresponding to the superheat condition. the absolute values of the signal are unimportant. Thus, a relatively low cost thermistor may be utilized as it has been found that even low cost thermistors provide relatively linear fixed differential determinations.  
  Control 27 is arranged to provide a stabilization period to determine the suction gas temperature, and then an opening of valve 30 to admit a sample of refrigerant from liquid supply conduit 20 to the expansion chamber 24 for setting the thermistor 25. The subsequent change of state of the saturated vapor on thermistor 25 is utilized to provide the saturated gas temperature at suction line pressure. Control 27 functions to compare the difference between these temperatures, which corresponds to the superheat condition temperature, with a desired preselected superheat condition temperature differential which may be programmed into control 27. Depending on the magnitude of the difference between the determined superheat condition and the preselected superheat condition, control 27 opens valve 32 to provide an incremental quantity of refrigerant fluid to suction line 18. Thus, the greater the difference between the determined and operating superheat conditions, the larger the quantity of refrigerant added to the system by the opening of valve 32. The variable addition of refrigerant may be controlled by controlling the time of opening of the valve 32 by control 27.  
  After the desired quantity of refrigerant is added to the refrigeration system I2 from supply 11, valve 32 is closed and the refrigeration system is allowed to operate to assimilate the added quantity of refrigerant. The superheat condition is then again determined by taking a new sample of liquid refrigerant from delivery conduit 20 and depending on the new determination of the difference between the operating superheat condition and the preselected superheat condition, additional refrigerant fluid may be delivered from supply 11 to the refrigeration system 12 by suitable opening of valve 32 by control 27. The superheat condition determination and incremental addition of refrigerant fluid is continued until the determined superheat condition of the refrigeration system is substantially equal to the preselected superheat condition.  
  The seriatim temperature determination and refrigerant addition functioning of the charging apparatus is carried on automatically and by causing the increments of refrigerant being added to the system to decrease in quantity as a function of the decrease in determined superheat condition from the preselected superheat condition. a zeroing-in of the refrigerant addition is effected to effectively avoid overcharging of the system while yet effecting the recharging of the system quickly and efficiently.  
  In the preferred embodiment. the superheat condition determination is effected in the expansion chamber means 23 mounted to the suction line 18. in one modified form of the invention as shown in FIG. 4 of the drawing. the thermistor 25 may be mounted directly within the suction conduit 18 with baffle 24a act ing as a chamber. The spray nozzle 4l extends through the wall of the conduit to adjacent the thermistor 25.  
  Any suitable control 27 may be utilized for performing the temperature determination comparisons and correesponding operation of valves 30 and 32. Illustrated in H0. 2, is one sensing means which may be employed in control 27 to provide the desired temperature comparing operation. Thus. as shown in H6. 2,  
 the sensing means or temperature comparing circuit portion 42 may comprise a constant current source 43 having connected thereacross a negative temperature coefficient thermistor 25, a resistor 45 and a series connection of a capacitor 44. A conventional operational amplifier 47 has its input connected across the resistor 45 and its output connected through a diode 46 to an output terminal 49. Also connected to output terminal 49 is a second capacitor 48 and a second resistor 50. The output signal taken between ground G and the output terminal 49 of amplifier 47 corresponds to the temperature differential determined by the successive voltages applied at the output of the circuit portion 42.  
  The operation of circuit portion 42 is as follows. The constant current source 43 provides a voltage across thermistor 25 proportional to the thermistor resistance. During the stabilization period to determine the suction gas temperature. capacitor 44 charges to this voltage across thermistor 25 and the current through R1 approaches zero. Thus the input to amplifier 47 is zero, and the charge stored on capacitor 44 is proportional to the suction gas temperature. When the test valve 30 is opened the vaporization of this spray on the thermistor causes a new charging current through resistor 45. This new current is offset and reduced by the charge already stored on capacitor 44 form the suction gas temperature measurement and is therefore proportional to the difference between the suction gas temperature minus the saturated liquid temperature at suction pressure. The time constant of resistor 45 and capacitor 44 is chosen such that capacitor 44 is charged to near full valve during the stabilization period and is long compared to the vaporization time of the liquid sprayed on the thermistor. Therefore, when the thermistor 25 has stabilized at the suction gas temperature and valve 30 is opened, an almost immediate voltage is imparted to the amplifier. The amplifier output is then provided at output thermal 49. The diode 46, resistor 50, and capacitor 48 function to provide a peak voltage measurement at output terminal 49. This is accom plished by storing the peak voltage from the amplifier output on capacitor 48. Thus, even though the vaporization of the liquid refrigerant on thermistor 25 maybe somewhat unstable, the peak voltage from the amplifier 47 is provided by capacitor to the output terminal 49.  
  Referring now to FIG. 3, the control 27 may comprise a plurality of control circuit portions 42, 42a, 42b  
 and 42c. The control portion 42 includes a constant current source 43 which may comprise a field effect transistor 52 connected in series with a direct current battery 53. The output of the amplifier 47 is delivered to a digital converter 54 and stores as 4 bit information in a conventional Quad latch 55 at the appropriate time. The 4 bit information from Quad latch 55 is stored in a conventional Read Only Memory (ROM) 56 which may be programmed to determine the required charge from the measured superheat information. By means of ROM 56. linerization and electronic calculations are eliminated. In the illustrated embodiment. the preselected superheat figure is an input to ROM 56 whereby the superheat condition sensed by thermistor 25 may be compared therewith.  
  Circuit portion 420 includes a ROM 57. This portion of the circuit is utilized to measure indoor air wet bulb depression and the circuit elements feeding to ROM 57 are similar to those feeding to ROM 56 and are identified by similar reference numerals but having the suffix a. ROM 57a stores a modified psychometric chart for wet bulb determination from the depression output of portion 42a and indoor dry bulb from portion 42b.  
  ln series with ROM 57 is a third ROM 58 wherein is stored the superheat information for the refrigeration system at various indoor wet bulb and outdoor dry bulb conditions. The outdoor dry bulb information is linearized in ROM 58. Circuit 42b provides the indoor dry bulb information to ROM 57. Circuit 42!) is generally similar to circiut 42 but omits a number of the elements thereof. Thus. circuit 4211 includes a thermistor 251). a direct current battery 53b, a transistor 52!), an operational amplifier follower 47!), an analog to digital converter 54b and a Quad latch 55b. Circuit portion 426 is similar to circuit portion 42b and provides outdoor dry bulb information to ROM 58. Circuits 42b and 42c include variable resistors 59b and 590. respectively. in series with transistor 52.  
  Referring now to FIG. 5, the timers and logic to perform the required operations are illustrated schematically. As shown. a single pole. double throw pressure switch 60 is provided in series with a single pole, single throw start switch 61 to feed P on the OR gate 62 until the solenoid charge valve 32 fills the system to the minimum starting pressure. The control is then switched to a timer 63 which allows for a stabilization period. During the stabilization period the charge representing the suction gas temperature is stored on capacitor 44 of circuit portions 42. At the end of the stabilization period, the Quad latch information is cleared. This reset also causes a timer 64 to open test valve 30. At the end of a short period of time, timer 64 closes the test valve and a timer 65 establishes another period of time to allow the thermistor 25 to cool by evaporation after being sprayed with the liquid refrigerant from conduit 20. During this time the saturated gas temperature is measured and the charge representative of the difference between the suction and saturated gas temperature is stored on capacitor 48. This charge is representative of the superheat at the end of this other period of time, and is read by AID converter 54 and set in Quad Latch S5. Simultaneously with the determination of the superheat, the wet bulb depression is measured by circuit portion 42a. The measurement is accomplished in a similar manner except that a water valve (not shown) is utilized to wet the thermistor 25a.  
  If the ROM 56 control determines that additional charge is necessary by comparing the superheat condition information from thermistor with the preselected superheat condition previously programmed into ROM 58. an -Undercharge&#34; lamp 66 is illustrated and the charging valve 32 is opened. The time during which the charging valve 32 is maintained open is controlled by a fourth timer 67 with the fourth timer being controlled by the percent charge output&#34; 561! of ROM 56 so that where the difference between the determined superheat condition and the preselected superheat condition is relatively large, valve 32 is maintained open for a long period of time and where the difference is smaller, the valve is maintained open for a shorter period of time automatically. The output of AND gate 73 is connected to the input of timer 63 to recycle the apparatus whenever an under charge has been indicated. A counter 68 may be provided for counting the number of cycles and may be arranged to limit the number of cycles to a preselected number.  
  AND logic elements 69, 70 and 73 may be provided for controlling correspondingly Over indicator lamp 7l Correct&#34; indicator lamp 72 and Under&#34; indicator lamp 73 which indicate correspondingly an overcharge, a correct charge, or an under charge condition of the refrigeration system. ROM 56 also provides an inrange signal which indicates that the conditions of su perheat, outdoor dry bulb temperature, or indoor wet or dry bulb are within a range considered allowable for proper charging of the system. The in range output of ROM 56 provides a signal to AND gates 69, 70 and 77 to indicate an in-range condition. A switch 73 is provided in series with charging valve 32 to allow the apparatus to be utilized as an indicator of the refrigerant system without operating the charging apparatus.  
  Thus. the present invention comprehends the provision of an improved charging apparatus utilizing a single condition-responsive circuit element and more specifically, a single temperature responsive element which determines the operating superheat condition of the refrigeration system for comparison with a preselected superheat condition permitting the charging of the system automatically without requiring the addition of any refrigerant in the event the system is properly charged. The increments of additional refrigerant so delivered may be varied as to quantity in direct corre spondence to the difference between the desired superheat condition and the actual opearting superheat condition so as to quickly zero-in on the fully charged condition while yet effectively preventing overshoot.  
  The apparatus and method of the present invention are extremely simple and economical while yet providing the highly desirable features discussed above.  
  The foregoing disclosure of specific embodiments is illustrative of the broad inventive concepts comprehended by the invention.  
 We claim.  
  1. The method of adding refrigerant to an operating undercharged refrigeration system comprising:  
 measuring the temperature of the suction refrigerant gas;  
 measuring the temperature of saturated refrigerant vapor at suction line pressure;  
 comparing said suction gas temperature and said saturated vapor temperature to determine the system superheat condition;  
 comparing the determined system superheat condition with a preselected desired system superheat condition; adding an incremental quantity of refrigerant to said 5 system; and  
 repeating said sequential temperature measuring and refrigerant adding steps until the determined system superheat condition substantially equals the preselected system superheat condition.  
 2. The method of adding refrigerant, to an operating undercharged refrigeration system of claim 1 wherein the amount of said incremental quantity is proportional to the difference between the determined and preselected system superheat conditions. 3. The method of adding refrigerant to an operating undercharged refrigeration system of claim I wherein the measurement of said temperatures is converted into electrical signals which are stored and utilized in said condition comparing step.  
  4. The method of adding refrigerant to an operating undercharged refrigeration system of claim 1 wherein the saturated vapor temperature is determined by utilizing a sample ofliquid refrigerant taken from said system.  
  5. The method of adding refrigerant to an operating undercharged refrigeration system of claim 1 wherein the saturated vapor temperature is determined by utilizing a sample of liquid refrigerant taken from said system, said vaporized sample being subsequently returned as refrigerant vapor to the system.  
  6. The method of adding refrigerant to an operating undercharged refrigeration system of claim I wherein means defining a chamber are caused to have a temperature corresponding to said suction gas temperature and said measuring of the suction gas temperature is effected by measuring the temperature of said chamber means.  
  7. The method of adding refrigerant to an operating undercharged refrigeration system of claim 1 wherein means defining a chamber are caused to have a temperature corresponding to said suction gas temperature and said measuring of the suction gas is effected by measuring the temperature of said chamber means, said saturated vapor temperature determination being effected by vaporizing in said chamber a sample of liquid refrigerant taken from said system and then measuring the temperature of said chamber means.  
  8. In a refrigerating system including a compressor, a condenser, a evaporator, a liquid line and first expansion means connecting the evaporator with the condenser. and a suction line connecting said evaporator with said compressor and having a suction port for introducing refrigerant into said suction line, a refrigerant charging apparatus comprising:  
 an expansion chamber mounted in mass heat transfer association with said suction line and having an outlet connected to said suction port;  
 means for sensing the temperature of said expansion chamber;  
 means for supplying liquid refrigerant to said expansion chamber from said liquid line including first valve means and second expansion means;  
 means for supplying additional refrigerant to said system including a source of pressurized refrigerant and second valve means; and  
 a control circuit connected to said temperature sensing means and said first and second valve means;  
 said control circuit having means adapted to be preset for a preselected system superheat condition. said temperature sensing means being arranged to determine the actual system superheat condition by first sensing the suction line temperature and then saturated vapor temperature as a quantity of refrigerant is admitted to said chamber by said first valve means under control of said circuit. said circuit being arranged to be subsequently operable to open said second valve means in the event the determined system superheat exceeds the preselected superheat condition thereby to add a quantity of refrigerant from said source to said suction line through said suction port.  
  9. The refrigeration system charging apparatus claim 8 wherein said temperature sensing means comprises a circuit including a thermistor.  
  10. The refrigeration system charging apparatus of claim 8 wherein said circuit is arranged to open said second valve means for a period of time proportional to the amount that the determined superheat exceeds the preselected superheat.  
  ll. The refrigeration system charging apparatus of claim 8 wherein said circuit is arranged to open said second valve means to add a quantity of refrigerant to said system and subsequently determine the system superheat condition seriatim repeatedly until the determined system superheat condition substantially equals to the preselected superheat condition.  
  12. In a refrigeration system having an evaporator. means for supplying liquid refrigerant to said evaporator for vaporization therein. and means for delivering refrigerant vapor from the evaporator, means for charging the refrigeration system comprising:  
 sensing means for determining the difference between the temperature of the refrigerant vapor and the saturation temperature of the refrigerant in the system;  
 refrigerant adding means responsive to the determined difference between said temperatures to add an incremental quantity of refrigerant to the system; and  
 control means causing seriatim a repetition of the determination of said temperature difference and addition of refrigerant until said temperature difference is substantially equal to a preselected temperature difference corresponding to a desired superheat condition of the refrigeration system.  
  13. The refrigeration system charging apparatus of claim 12 wherein said refrigerant adding means delivers the refrigerant to said means for delivering refrigerant from the evaporator.  
  14. The refrigeration system charging apparatus of claim 12 wherein the sensing means includes controlled valve means for sampling a portion of the liquid refrigerant from the liquid supplying means.  
  15. The refrigeration system charging apparatus of claim 12 wherein the sensing means inculdes first controlled valve means for sampling a portion of the liquid refrigerant from the liquid supplying means. and the refrigerant adding means includes a supply of refrigerant under pressure and a second controlled valve means for controlling delivery of the refrigerant from said supply to said system.  
  16. The refrigeration system charging apparatus of claim l2 wherein the sensing means includes first con trolled valve means for sampling a portion of the liquid refrigerant from the liquid supplying means. the refrigerant adding means includes a supply of refrigerant under pressure and a second controlled valve means for controlling delivery of the refrigerant from said supply to said system. and said control means includes means for causing seriatim a. determination of the temperature of the refrigeration vapor.  
 b. operation of said first controlled valve means to provide a sample of the liquid refrigerant.  
 c. determination of the saturation temperature of said sample. and  
 (1. operation of said second controlled valve means to add an incremental quantity of refrigerant to the system in the event the determined difference between said temperatures is greater than said preselected temperature difference.  
  17. The refrigeration system charging apparatus of claim 12 wherein said control means defines means for causing the amount of said incremental quantity added to the system to be a direct function of said determined temperature difference.  
  18. The refrigeration system charging apparatus of claim 12 wherein the sensing means includes first controlled valve means for sampling a portion of the liquid refrigerant from the liquid supplying means. the refrigerant adding means includes a supply of refrigerant under pressure and a second controlled valve means for controlling delivery of the refrigerant from said supply to said system. said control means includes means for causing seriatim a. determination of the temperature of the refrigeration vapor.  
 b. operation of said first controlled valve means to provide a sample of the liquid refrigerant.  
 c. determination of the saturation temperature of said sample. and  
 d. operation of said second controlled valve means to add an incremental quantity of refrigerant to the system in the event the determined difference between said temperatures is greater than said preselected temperature difference. and said control means further includes means for causing the amount of said incremental quantity added to the system to be a direct function of said determined temperature difference whereby said temperature difference may be made to be substantially equal to said preselected difference with an effectively minimized number of incremental refrigerant additions.  
  19. The refrigerant system charging apparatus of claim 12 wherein said sensing means comprises a circuit portion including a thermistor, a capacitor. and a resistor electrically connected to determine said temperature difference.