US2387604A - Automatic control system - Google Patents

Description

Oct. 23, 1945. A N N 2,387,604

AUTOMATI G CONTROL SYSTEM Filed May 28, 1941 zac 23B INVENTOR Alwim B. Nczwion... BY

ATTORNEY H I H I I Patented Oct. 23, 1945 AUTOMATIC CONTROL SYSTEM zuwai B. Newton, Minneapolis, Minn., assignor to Min'neapolis-floneywell Regulator Company, LMinneapolis, Minn, a corporation of Delaware Application May 23, 1941, .Serial No. 395,561

'17 Claims.

proved meansfor modifying the operation of a condition responsive switch or equivalent (the condition being pressure or temperature or the like) device in response to conditions at a plurali-ty of remote points.

Another-object is tocorrtrol theamount of com pressor operation ina refrigerating system having a plurality of -.evaporators in accordance with the total refrigerating requirements of a plurality of spaces-being served.-

Another object to-adjustably bias a condition responsive switch E y means of an electromagnetic device, the energization-of which is controlled jointly by control instruments located at a plurality of difierent points.

Further objects andadvarntagesof my invention will become apparent from the following detailed description- .and annexed drawing, the single figare of which represents a refrigerating system -for a plurality of compartments, my invention being embodied the control arrangement for the '1 system.

Referring to the'drawnig, a refrigeration system of the compression type is shown, the system having a compressor motor controlled .by the particular control arrangement constituting oneform of my invention. Numeral i designates the compressor which is driven by anelectric motor H through a belt 42 The compressor discharges into a condenser 13 through a pipe 14 and the condenser 13 is connected to a plurality of evaporators A, B, and NC by means of a pipe 16 having branches ISA, [6B, and 1-50 connected to the respective evaporators, the evaporators being disposed in separate compartments to be refri erated 18A, 18B and 18C. Numeral l9 designates the suction pipe of the compressor which has branches ISA, I93 and 190 connected to the outlets of the respective evaporators. Interposed in the supply pipes .I BA, IE3 and 160 are thermostatic expansion valves A, 15B and IEC re spectively. these valves being of a well known type adapted to maintain a constant number of degrees of superheat at the outlets of their respective evaporators. The respective valvesare connected tothermal bulbs 22A,22B and'22Cwhich are adj aann cent the outlets of the evaporators, by means of capillary'tubes 23A, 23B and 23C. The operation of these expansion valves is well known in the art and need not be described in further detail.

The controls .for the compressor motor include a controller designated .by the reference character 25 which comprises a generally rectangular metal casing 2-6, .the casing having a flanged opening 21 as shown, through which electrical leads controlling the compressor motor -I I pass to the interior of the casing.

Within the casing 26 is a horizontal shelf 29 having a portion 30 forming a bracket which may be suitably secured to a side wall of the casing 26. The shelf 29 is primarily supported by standards BI and 32 upstanding from the bottom of the casing 26. Numerals .35 and 3B designate bolts which extend through the standards 31 and 82 which engage the shelf 29 in screw-threaded relationship. Supported on the shelf 29 is a, snap switch .31 :is enclosed within a Bakelite housing detail in the application of Albert Baak, Serial No. 307,991, filed-on December '7, 1939. Thesnap switch 3'1 is enclosed within a bakelite housing and has on and on positions and is of the type which tends to remain in the position to which it is opera-ted. The snap switch 31. has an operating stem 38 extending downwardly therefrom, the stem 38 having two spaced horizontal slots or openings therein. As shown, the snap switch 31 has two contact terminals formed by screws 39 and 40 for making electrical connections to the switch.

The operating mechanism for the snap switch 31 includes a, pressure responsive bellows enclosed within a housing 41 at the lower portion of the casing 2-6. The housing 41 is flanged and the flange is secured to the lower side of the casing 26 by .screws which include the screws 35 and 42. The bellows within housing '4'! is eXDa-nsible and contractible and is connected to the suction pipe of the compressor by a tube :43. If desired the bellows could be actuated directly by evaporator temperature. The operating end of the bellows operates a bellows post 44 which extends through a nut 45 within the casing 26. The nut 45 cooperates with a spring within housing M which opposes the bellows, and by adjusting the nut 45 the tension of the spring and correspondingly the loading on the bellows may be varied. At the upper end of the bellows post 44 is a ball 46 loosely engaged within an opening in an operating lever 41, the right end of which is engaged in the upmr one of the slots in the switch operating stem 38. Numeral 48 designates a leaf spring secured at one end to the lever 41 by rivets or the like with the other end engaging the upper side of ball 46. Numeral 49 designates a similar leaf spring secured to the opposite side of lever 41 and having an opening through which the upper end of the bellows post 44 extends with the leaf spring 49 engaging the lower side of the ball 46. The arrangement just described forms a strain release connection between the bellows post 44 and the operating lever 41.-

The left end of the operating lever 41 is disposed between two cams 52 and 53, each of which has a spiral contour. The cam 52 is mounted on a shaft which extends through a side wall of the casing 26 and which is rotatable by a manual knob 54 outside of the casing. Adjacent the knob 54 is a dial 55 movable with respect to an index marker for indicating the position of the cam 52. The cam 53 is mounted on a shaft which extends through a side wall of the casing 26 and which is rotatable by a manual knob 58 outside of the casing, and there is a graduated dial 51 similar to dial 55 adjacent the manual knob 56.

From the foregoing, it will be seen that the lever 41 is a floating lever and that it left end moves between the cams 52 and 53 which act as stops. The lever 41 is moved by the suction pressure affecting the bellows within housing 4|. When the suction pressure rises, the bellows within housing 4| is expanded and the bellows post 44 moves lever 41 upwardly by reason of engagement of ball 48 with the leaf spring 48. When the left end of lever 41 engages cam 52, the cam acts as a stop for the lever 41 and the lever 41 is then constrained to pivot in a counter-clockwise direction about the cam which acts as a fulcrum. Counter-clockwise movement of the right end of lever 41 moves the operating stem 38 of switch 31 upwardly so as to move the switch to closed position. When the switch 31 moves to closed position the circuit for the compressor motor is completed as follows: from a line conductor 68 through wire 6| to terminal 40 of the snap switch through the snap switch to terminal 39, wire 62 through the compressor motor and through wire 83 back to line conductor 64. The parts are normally so arranged and adjusted so that switch 31 will be closed at suction pressure high enough to insure that the evaporator temperature has risen high enough to defrost it after each cycle of the compressor. In the event there should be a rise in suction pressure when the snap switch is closed, as described, upward movement of the ball 46 with respect to lever 41 is permitted by virtue of the resiliency of the leaf spring 48. The point, that is the pressure, at which lever 41 will begin to move in a counterclockwise direction so as to close the snap switch may be adjusted by rotatably adjusting the cam 52 which, as pointed out above, has a spiral contour so that the point of engagement between its edge and the end of lever 41 may be raised and lowered by rotating the cam. After the compressor has started in operation the suction pressure will fall causing the bellows within housing 4| to contract, thereby moving the bellows post 44 downwardly until the left end of lever 41 engages cam 53. When this happens the lever 41 will pivot in a clockwise direction about the cam 53 which acts as a fulcrum, the right end of lever 41 moving downwardly so as to move the operating stem 38 downwardly to open the snap switch 31. The pressure at which lever 41 will thus move in a clockwise direction for opening the switch and stopping the compressor may be adjusted by adjusting the position of cam 53 which also has a spiral contour, as pointed out above, that is, the point at which lever 41 engages the edge of the cam may be raised and lowered by rotatably adjusting the cam.

The snap switch 31 may also be operated by a device responsive to the discharge pressure of the compressor. This device includes an expansible and contractible bellows enclosed within a housing 85 which has a flange secured to the lower side of the casing 26 by screws 66 and 61. The bellows within housing 85 is connected to the discharge pipe M of the compressor by a tube 68. The bellows within housing 65 operates a bellows post 69 which extends through a nut 18 inside of the casing 26. The nut 18 cooperates with a spring within housing 65 which opposes the bellows therein, and by adjusting the nut 10 the tension of the spring and correspondingly the loading of the bellows within housing 65 can be varied. Numeral 1| designates a small lever having ears pivotally engaging a pin 12 extending outwardly from the back of the casing 26. The right end of lever 1| is engaged in the other of the slots in the operating stem 38 and the left end of the lever 1| may be actuated by a screwthreaded member 14 carried by the end of the bellows post 69; that is, when the compressor discharge pressure increases to a predetermined relatively high value, the bellows within housing 65 expands moving member 14 into engagement with lever 1| causing lever 1| to rotate clockwise so as to move operating stem 38 downwardly opening snap switch 31 the snap switch may be thus opened even though the suction pressure is at a value at the time to have the switch closed. The strain release connections between bellows post 44 and lever 41 will permit the operating stem 38 to be moved downwardly by the discharge pressure responsive device even though the lever 41 is engaging cam 52 at the time, the leaf springs 48 and 49 permitting relative movement of lever 41 and the ball 46 as pointed out above.

The structure so far described has heretofore been used in the art for controlling a compressor in response to suction pressure and head pressure. My invention comprehends employing additional mechanism in conjunction with the controller whereby the compressor is controlled in response to the temperature within the refrigerated compartments as well.

Numeral 18 designates an electromagnetic device comprising a winding 19 supported by means of a bracket extending outwardly from the side of the casing 26. The winding 19 has an armature 8| cooperating therewith, the lower part of which carries a member 82 having a knife edge 83. The numeral 84 designates a lever having a boss 85 which normally engages the underside of shelf 29, the right end of the lever extending through an opening in the side of the casing 28 and the right end of the lever having a crimped portion 86 as shown which engages the knife edge 83 so that the lever 84 may pivot about the member 82. The left end of the lever 84 has a finger 81 normally engaging the leaf spring 48 directly above the ball 46 so that downward force exerted by the left end of lever 84 is in line with the force exerted through bellows post 44 and is directly opposed thereto. The right end of lever 84 is normally urged into engagement with the knife edge 83 by a coil spring 88, the upper end of which is attached to an ear 89 on lever 84 and the lower end of which is attached to a member 90 engaged on a screw 9! extending through a bracket 92 extending outwardly from the side of the casing 26. The tension of spring 88 may be adjusted by adjusting the screw 91. Numeral 93 designates a guide member attached to member 98 which moves in a slotinthe side of casing 26.

The winding 19 of the device 18 normally oarries a certain amount of current, and its mag netic field urges the armature 81 in an upward direction with a force depending upon the amount of current flowing through the winding 19. The upward force exerted on the right end of lever 84 tends to cause lever 84 to fulcrum about the point at which boss 85 engages the shelf '29, the left end of lever 84 exerting a force as described above opposing that of the bellows within ho11s ing 4! actin through the bellows post 44. In

other words, the device 18 provides a resistance to upward movement of lever 41 and closure of switch 31 which raises the cut-in point of the switch an amount depending upon the energizetion of winding 19. In other words, when lever 41 is moved upwardly so as to engage cam 52 for,

closing the snap switch 31, the lever 84 must be rotated slightly in a clockwise direction against the upward pull exerted on its right end by the armature 85. On the other hand, when the suction pressure is decreasing, the device 18 assists downward movement of lever 4'! and raises the cut-out point of switch 3! by a similar amount depending upon the energization of winding 19.

Winding 19 is controlled by an electric circuit which extends through a resistance type thermostat disposed in each of the compartments 18A, 18B and 18C, these thermostats being designated by the reference characters 95A, 95B and 95C, respectively. The thermostat 95A comprises an expansible and contractible bellows 96A containing a volatile liquid. the movable end of the bellows having a stem which engages a pivoted slider or arm 91A, the left end of which slides over an electrical resistance 98A. The slider 91A is normally biased in a counter-clockwise direction by a coil spring 99A. When the temperature in compartment ISA rises, the bellows 96A expand moving the end of slider 81A upwardly along resistance 98A and increasing the resistance in circuit with winding 19 as will presently appear. When the temperature in compartment lBA decreases, the bellows 96A contacts moving the slider 91A downwardly along resistance 98A.

The thermostats 95B and 95C are identical with thermostat 95A and the elements of these thermostats are designated by the same numerals with identifying letters 50 that these thermostats need not be further described.

Numeral I designates a high limit thermostat in the compartment l8A which comprises a normally closed switch which is opened when the temperature in compartment lBA rises to a relatively high value beyond which it is not desired that the temperature rise. Numeral lfll designates a low limit thermostat comprising a normally opened switch which closes when the temperature in compartment 480 falls to a relatively low value below which it is not desired that the temperature in compartment 180 should go. Numeral 102 designates a single-pole, doublethrow manual switch comprising a switch arm I03 and terminals I84 and IE5, the purpose of which will be described presently.

The winding 19 is normally energized through an electrical circuit as follows: from wire W8 through winding 719. wire 18!], wire H0, part of resistance 98C, slider 97C, wire I, wire H2, part of resistance 98B, slider 91B, wire H3, part of resistance 98A, slider 91A, wire H4, wire 5, high limit thermostat 108 to wire 416, the wires I08 and I 16 being connected to a suitable source of power not shown. From the foregoing, it is apparent that the energization of winding 19 depends upon the amount of current flowing there through which is determined by the positions of thermostats 91A, 91B and 91C, that on the amount of resistance in the circuit of the winding. When the temperatures in the compartments I8A, 18B and I are at predetermined values, the thermostats have their sliders 91 at the mid points of their respective resistances as shown. Under these olrcmnstances, the winding 19 carries a predetermined current, and its energization provides a predetermined force acting through lever 84 to oppose the bellows within housing 4|. Thus, the normal cut-in and cut-out points of the switch 31, as earlier determined by the settings of cams 52 and 53, are raised a predetermined amount as described above determined by the energization of winding 18. The compressor will now be started and stopped at suction pressures calculated to produce sufficient compressor operation to meet the requirements of all of the compartments l-8A, RB and 180. As the temperature in any compartment rises above the desired value, its respective thermostat will move its slider upwardly along its respective resistance thereby increasing the amount of resistance in circuit with winding 19 so as to thereby decrease the energization of the winding. Upon this occurring, the upward force exerted on armature 8| will be decreased and correspondingly the downward force exerted by finger 81 opposing upward movement of bellows post 44 will be reduced. Thus, there will be less resistance offered to expansion of the bellows within housing 41 and the left end of the lever 41 will engage cam 52 at a lower pressure than previously, and the switch 31 will be closed at this lower pressure. In other words, the compressor will now be cut in sooner than before to meet the increased cooling requirements. Likewise. the cut-out point of switch 31 will be correspondingly lowered due to the reduced downward force exerted by the left end of lever 84, that is there will be less force assisting the downward movement of lever 41 towards the cam 53. Whenever there is a decrease in temperature in any of the compartments [8A, IBB or I80. the thermostat of that compartment will move its respective slider downwardly along its associated resistance, thereby decreasing the resistance in circuit with winding 19 and increasing the energization there of. Thus, the armature 8| will be pulled upwardly with increased force and the finger 81 of lever 84 will exert an increased downward force in bellows post 44. The suction pressure will now have to rise a higher value than originally in order to overcome this increased force to bring about the closure or the switch 31,. Similarly. the increased downward force exerted by the left end of lever 84 will correspondingly raise the cut-out point of switch 31.

From the foregoing, it is to be seen that when there is an increase in temperature in any compartment, the compressor will .be cut in at a lower value of suction pressure; that is, after it has been stopped it will be started normally after a shorter delay than usual. Also, when there has been a rise in temperature in any compartment, the compressor will be shut down at a lower suction pressure, or in other words it will operate longer than normally. It is to be seen therefore that when there is a need for increased refrigeration the on cycles of the compressor are increased in length of the off cycles are shortened, the operation of the compressor being through a lower range of suction pressure. When there is a demand for reduced refrigeration in any compartment, the relative duration of the compressors on and off cycles is varied oppositely; that is, the on cycles are reduced in length and the off cycles are lengthened. The thermostats 91 of all the compartments are simultaneously eflective of course to control the electromagnetic device I8, and its energization depends upon the cumulative effect of all thermostats so that the operating pressures of switch 31 depend upon the temperatures in all the compartments and consequently the amount of compressor operation. and the pressures at which it takes place depends u on the requirements of all the compartments. Thus, the amount of compressor operation is governed in accordance with the total amount of refrigeration required.

Normally the temperatures in the various compartments will generally tend to rise and fall together in accordance with the on and off cycles of the compressor, that is. the temperature in all the compartments tending to fall when the compressor is operating so as to be raising the cut-out setting while the compressor is operating. Generally the temperature will have risen in all the compartments before the compressor starts and the controls may be so arranged that normally all the evaporators defrost before the compressor starts.

In the event that the temperature in compartment I8A should rise to the setting of the high limit thermostat I00, this thermostat will open and inerrupt the circuit of winding I9. This will of course completely deenergize the winding I9 releasing the right end of lever 84 so that no pressure is exerted downwardly by finger 81 at the left end of lever 84. Thus, there will be no additional loading applied to the controller 26 and it will operate at pressures determined by the settings of cams 52 and 53. In other words, the cut-in. and cut-out points of switch 3'l will be at their lowest respective values depending upon the settings of cams 52 and 53 at the time. Thus, the amount of refrigeration produced will be a maximum for the existing settings of cams 52 and and this amount of refrigeration should normall be sufiicient to prevent the temperature in compartment I8A from rising appreciably above the setting of thermostat I00. A high limit thermostat similar to thermostat I00 can of course be placed in each of the compartments in series with the winding 19.

Referring to the low limit thermostat IOI in compartment I80, when the temperature in this compartment falls to a relatively low value for which the thermostat is set this thermostat will close, completing a circuit through winding I9 which shunts all of the thermostats 95 when manual switch. I02 is in the position shown. This circuit is as follows: from wire I08 through winding I9, wire I09, wire I20, terminal I04, blade I03, wire I2I, thermostat IOI, wire I22, wire II5, thermostat I00, and wire II6. This circuit does notinclude the resistances of the thermostats 95 and thus the amount of current flow through winding 19, and its energization will therefore be all at a maximum. correspondingly, the amount of downward force exerted by finger 81 in line with bellows post 44 will be at a maximum and the cut-in and cut-out points of switch 31 will now beat their maximum values for the existing settings of cams 52 and 53. Thus, the amount of refrigeration produced will be at a minimum so as to prevent the temperature in compartment I00 from further falling below the setting of thermostat IOI.

If desired, the manual switch I02 may be moved to its other position wherein blade I03 engages terminal I05. With the manual switch so positioned only the thermostats A and 95B are shunted, the circuit through the low limit thermostat and through winding I9 now being as follows: from wire I08, through winding I9, wire I09, wire IIO, part of resistance 98C, slider 91C, wire III, wire I23, terminal I05, switch blade I03, wire I 2|, thermostat I 0|, wire I22, wire II5, thermostat I00 and wire IIG. Inasmuch as this circuit shunts the thermostats 95A and 95B, the resistance in circuit with winding I9 is substantially reduced and its energization correspondingly increased to raise the cut-in and cut-out points of the switch 31 and reduce the amount of refrigeration in the same manner as explained above. If desired, a low limit thermostat similar to thermostat IOI and similarly wired might be placed in each of the other compartments I8A and I8B. I

From the foregoing, those skilled in the art will readily appreciate that I have provided a control arrangement for a multiple evaporator system wherein thecompressor is conveniently and advantageously controlled primarily in re sponse to suction pressure. with the amount of compressor operation being varied dependently upon the amount of refrigeration required of the evaporators. The apparatus utilized is simple in construction and trustworthy in operation, not requiring complicated or delicate parts. The control arrangements are such that high and low limit thermostats may very conveniently be made of use in any or all compartments to be refrigerated.

The single embodiment of my invention which I have disclosed is illustrative of its preferred form although many variations and modifications therein will occur to those skilled in the art. My disclosure is therefore to be interpreted in an illustrative rather than a limiting sense, and the scope of my invention is to be determined only in accordance with the claims appended hereto.

I claim as my invention:

1. In apparatus of the character described, in combination, an automatic control device comprising a movable element, pressure operable means for actuating said element, means resisting movement of said element, and space temperature responsive means associated with said resisting means for varying the resistance offered to movement of said element, said space temperature responsive means comprising an electromagnetic device associated with said element and means for proportionately varying the energization of said device in accordance with temperature changes.

2. In apparatus of the character described, in combination, an automatic switch having an operating member, pressure actuatable means for moving said member, temperature changing means controlled by said switch, means for biasing said operating member comprising an eleca HUMIDITY REGULATION.

tromagnetic device and thermostatic means responsive to the temperature in a space for proportionately varying the energization of said device for modifying the bias of said member in accordance with temperature variations in the space.

3. In apparatus of the character described, in combination, an automatic switch having an operating member, pressure actuatable means for moving said member, temperature changing means for a plurality of spaces controlled by said switch, means for biasing said operating member comprising an electromagnetic device and a plurality of thermostats, one in each space for varying the energization of said device for modifying the bias of said member.

4. In a refrigerating system, in combination, a compartment to be refrigerated, an evaporator in said compartment, means including a compressor for circulating refrigerant through said evaporator, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electromagnetic device, a thermostat in said compartment arranged to proportionately vary the energization of said device in accordance with temperature changes whereby the bias of said switch operating member is varied so as to control the amount of compressor operation in accordance with refrigeration requirements.

5. In a refrigerating ystem, in combination, a plurality of compartments to be refrigerated, an

evaporator in each compartment, means includ- I ing a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuat'able means for moving said member, means for biasing said operat ing member, said last means including an electromagnetic device, a thermostat in each compartment, means whereby said thermostats jointly control the energization of said device whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements.

6. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means including an operatin member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, means for controlling the bias exerted by said biasing means including a thermostat in each compartment, the thermostats being arranged to jointly vary the bias of said switch operating member to control the amount of compressor operation in accordance with the total refrigeration requirements.

7. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means includin a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being arranged to jointly control the energization of said device, whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements.

8. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means, including an operating member controlling said compressor, pressure actuable means for moving said member, means for biasing said operating member, said last means including an-electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being arranged to jointly control the energization of said device whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements, and a, thermostat responsive to a predetermined temperature in one of said compartments associated with said device for substantially changing the energization of said device to vary the bias of said switch operatin member and the amount of compressor operation accordingly.

9. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being arranged to jointly control the energization 'of said device whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accord- I ance with the total refrigeration requirements,

and a thermostat responsive to a relatively high temperature in one of said compartments controlling said device for substantially changing the energization thereof to vary the bias of said switch operating member in a direction to substantially increase the amount of compressor operation.

10. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being connected in series with said device for jointly controlling the energization thereof whereby the bias of said switch operating memher is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements.

11. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means ineluding an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being connected in series with said device for jointly controlling the energization thereof whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements, and a thermostat in one of said compartments responsive to a predetermined temperature therein for interrupting the circuit of said device to substantially decrease the energization of said device for varying the bias of said switch operating member and the amount of compressor operation correspondingly.

12. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member, means for biasing said operating member, said last means including an electrical device responsive to the amount of current flowing therethrough, a variable resistance type thermostat in each compartment, said thermostats being connected in series with said device for jointly controlling the energization thereof whereby the bias of said switch operating member is varied so as to vary the amount of compressor operation in accordance with the total refrigeration requirements, and a thermostat in one of said compartments responsive to a predetermined temperature therein for shunting at least one of said aforementioned thermostats to substantially increase the energization of said device for varying the bias of said switch operating member and the amount of compressor operation corresponde y.

13. In a refrigerating system, in combination, a plurality of compartments to be refrigerated, an evaporator in each compartment, means including a common compressor for circulating refrigerant through said evaporators, switch means including an operating member controlling said compressor, pressure actuatable means for moving said member in response to suction pressure for producing cycling operation of the compressor,

means for biasing said operating member, means member to control the cut-in and cut-out points of said switch means, the temperatures in the compartments normally rising to defrosting values of the evaporators during ofi cycles of the compressor and the thermostats lowering the cutin point of the switch means, the thermostats acting to raise the cut-out point of the switch means as the compartment temperatures fall during operation of the compressor.

14. In a system of the class described comprising in combination, a plurality of spaces whose temperature is to be controlled, cooling coils in said spaces, a refrigeration system comprising compressor means and condenser means for supplying refrigerant to said coils, means for maintaining the suction pressure of said refrigerant between definite values, and means for changing said values in accordance with the temperature in each of said spaces.

15. In a system of the class described comprising in comblnation, a plurality of spaces whose temperature is to be controlled, cooling coils in said spaces, a refrigeration system comprising compressor means and condenser means for supplying refrigerant to said coils, means for maintaining the suction pressure of said refrigerant between definite values, electrical means for biasing said maintaining means, and means for varying the flow of current through said electrical means in proportion to the temperature changes in each space for varying said values.

16. A system of the class described, comprising, in combination, a plurality of spaces whose temperature is to be controlled, means for supplying a temperature changing fluid to said spaces, means acting on said fluid to cause it to change the temperature of said spaces, means responsive to a condition related to the temperature of said fluid for controlling said last named means to maintain said condition between definite values, and means for changing said values in accordance with the temperature in each of said spaces.

17. A system of the class described, comprising, in combination, a plurality of spaces whose temperature is to be controlled, means for supplying a temperature changing fluid to said spaces, means acting on. said fluid to cause it to change the temperature of said spaces, a controller responsive to a condition related to the temperature of said' fluid for controlling said last named means to maintain said condition within predetermined limits, electromagnetic means associated with said controller in a manner to bias it and hence vary said limits, and means for varying the flow of current through said electromagnetic means in accordance with the change of temperature in each of said spaces.

ALWIN B. NEWTON.

CERTIFICATE OF CORRECTION. Patent No. 2,587,6ou. October 25, 19L 5Q AININB. NEWTON.

It is hereby certified that error appears in the printed Specification of the above numbered patent requiring correction as follows; Page 1, sec 0nd column, line 21, for "is enclosed within a Bakelite housing" read --which is of the same type disclosed in -g and that the said Letters Pat wnt should be read with this correction therein that the same may conform to the record of the case in the Patent Office.a

Signed ahd sealed this 22nd day of January, A. D. 19146,

Leslie Frazer (Seal) First Assistant Commissioner o Patents

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