US2064010A - Refrigerating apparatus - Google Patents

Description

Dec. 15, 1936. '7 H, B HULL 2,064,010

REFRIGERATING APPARATUS Filed May 25, 1934 5 Sheets-Sheet 1 L l L 48 24 0 J I 4 36 2 3 'u f j L 22 I a?) I his W5.

Dec. 15, 1936. H. B. HULL REFRIGERATING APPARATUS 3 Sheets-Sheet 2 Filed May 25, 1934 v his mum Dec. 15, 1936. H. B. HULL 2,064,010

REFRIGERATING APPARATUS Filed May 25, 1934 5 Sheets-Sheet s Patented Dec. 15, 1936 PATENT OFFICE REFRIGERATING APPARATUS Harry B. Hull, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application May 25, 1934, Serial No. 727,542

13 Claims.

This invention relates to refrigerating apparatus and more particularly to the control of such an apparatus.

Provisions have heretofore been made for automatically and temporarily increasing or permitting the temperature of an evaporator of a refrigerating system to be increased at predetermined timed intervals in order to initiate or effect melting of frost from walls of the evaporator. Such provision has as 'far as I am aware ordinarily effected periodic defrosting of the evaporator irrespective of the amount of frost accumulated on the walls thereof. It has been found that defrosting of an evaporator of a refrigerating system at predetermined timed intervals is not entirely satisfactory because it quite frequently occurs that the temperature of an evaporator is increased, to effect defrosting thereof, when such defrosting is notnecessary.

20 The amount of frost accumulated on the cooling surfaces of an evaporator ofa refrigerating system over a predetermined interval of time varies in accordance with certain food products placed in the compartment being cooled by the evaporaton For example, certain food products are of a greater moisture content than other food products and if a large number of food products containing a considerable amount of moisture are placed in a refrigerated compartment in which an evaporator is disposed the cooling surface of the evaporator will be quickly covered or coated with a layer of frost due to the cooling efiect produced by the evaporator causing moisture to be withdrawn from the food products and becoming condensed on the cooling surfaces of the evaporator. However, 1 if the number of food products containing a; considerable amount of moisture stored in the refrigeratedcompartment ,is reduced to a minimum it 40 will require a longer interval of time for the cooling surfaces of the evaporator to become coated or covered with frost. Since it is only after the frost has accumulated on the cooling surfaces of an evaporator to apredetermined 45 thickness that it tends to insulate the evaporator from the air to be cooled thereby and renders the refrigerating system inefiicient in operating no advantage is obtained by periodically defrosting the evaporator prior to the time the .frost 50 accumulation thereon becomes detrimental.

' Periodic defrosting of the evaporator prior to the time the frost thereon becomes detrimental to the operation of the refrigerating system causes temporary non-freezing actions of the evaporator thus retarding fast freezing of sub- 6 stances, contained in trays and placed in thermal contact with the evaporator, to be frozen. In addition, defrosting of an evaporator when not essentially required causes undue strain, and wear on operating parts of the refrigerating 10 system. My invention is therefore directed to overcoming the difficulties and disadvantages of the conventional refrigerating system in which defrosting of the evaporator occurs periodically irrespective of the amount of frost accumulated on the evaporator and has to do with the provision of an improved system in which the evaporator will be defrosted only when defrosting thereof is necessary as determined by the frost formation thereon.

One of the objects of the present invention is to provide an improved, refrigerating system including means for automatically and periodically defrosting the evaporator of the system irrespective of the temperature thereof.

Another object of the invention is to provide a refrigerating system with a means for: automatically and periodically defrosting the evaporator of the system only when defrosting thereof is necessary.

A further object of the invention is to provide a refrigerating system with means for automatically defrosting the evaporator of the system which means is normally ineffective and rendered effective solely by a predetermined thick ness of frost accumulated on the evaporator.

A still further object of the invention is to provide a refrigerating system with a chronometrically operated device, adapted to initiate defrosting of the evaporator of the system at 40 predetermined time intervals, and to construct and associate the device with the system so that it is normally ineffective, thereby permitting the evaporator to produce a refrigerating effect until frost accumulated on walls of the evaporator attains a thickness suflicient to cause ineflicient operation of the refrigerating system and so that the device will thereupon become effective to defrost the evaporator.

Further objects and advantages of the present ley connections 32.

invention will be apparent from the following description, reference being bad to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. l discloses a refrigerator cabinet having my invention embodied therein and diagrammatically showing certain elements of a refrigerating system associated with the cabinet;

Fig. 2 is a front view of a chronometric device associated with the refrigerating system disclosed in Fig. 1 and showing the device in normal position relative to the cooling unit or evaporator of the refrigerating system.

Fig. 3 is a view of the chronometric device similar to Fig. 2 but shows the device in a position after having moved a feeler arm associated therewith toward the evaporator of the refrigerating system;

Fig. 4 is a view of the chronometric device showing the feeler arm associated therewith moved into engagement with a layer of frost accumulated on a wall of the evaporator and showing an electric switch associated with the device moved into open position;

Fig. 5 is an enlarged view taken on the lines 5-5 of Fig. 2 showing certain of the parts associated with the chronometric device in section;

Fig. 6 is an enlarged view taken on the lines 6-6 of Fig. 2 showing certain of the parts associated with the chronometric device in section; and

Fig. '7 is an enlarged cross sectional view taken on the lines (-1 of Fig. 2 showing the mounting of certain parts operated by the chronometric device.

Referring to the drawings, for the purpose of illustrating my invention,'Ihave shown in Fig. 1, thereof a refrigerating system comprising a compressor 20 adapted to compress a refrigerant, such as sulphur dioxide, and to forward the refrigerant under pressure through a pipe 2| to a condenser 22 where the compressed refrigerant is liquefied and collected in a receiver 23. From the receiver 23 the liquid-refrigerant is forwarded through the supply conduit 24 to an evaporator 25 mounted in the upper portion of a refrigerator cabinet 26. The evaporator may be of any conventional type and is preferably of the sheet metal variety and providing a sharp freezing chamber within the food storage compartment 2'! of cabinet 26 for the reception of ice making receptacles or trays 28. Any of the conventional and well-known float, expansion or restriction devices (not shown) may be employed for admitting liquid refrigerant to the evaporator 25 from the conduit 24 or for maintaining a substantially constant level of liquid refrigerant in the evaporator. Liquid refrigerant within the evaporator 25 absorbs heat and vaporizes, this vapor being returned to the compressor 20 through the gaseous refrigerant return conduit or pipe 29. The compressor 20 is driven by an electric motor 3| through suitable belt and pul- The motor 3| is supplied with electric energy through an electrical circuit which will be hereinafter more fully described.

A control switch 33, such as the control mechanism disclosed in the patent to Otto M. Summers, No. 1,802,486, issued April 28, 1931, is connected by the pipe or conduit 34 with the low pressure or gaseousrefrigerant conduit 29. As the pressure of refrigerant in conduit 29 increases or decreases uniformly in accordance with the temperature of the refrigerant in evaporator 25 the control switch is actuated by an expansible bellows 36, connected with conduit 34, to normally maintain the evaporator 25 and consequently compartment 21 between predetermined temperature limits by opening and closing an electric circuit leading to motor 31. The switch 33 thus provides alternate operating and idle periods of the motor 3| and compressor 20 in accordance with the temperature of evaporator 25 to cyclically circulate refrigerant through the evaporator. The foregoing description and disclosure of a refrigerating system or apparatus is conventional and well known to those skilled in the art of refrigeration. For this reason the description of the refrigerating system is made brief and the system is only diagrammatically disclosed.

Evaporators employed in refrigerating systems of the type disclosed ordinarily have cooling surfaces exposed to the air within the food storage compartment of a refrigerator cabinet and these cooling surfaces are usually maintained at such low temperatures that moisture condenses and accumulates thereon in the from of a layer of frost. It has been found that frost after accumulating on an evaporator beyond a certain thickness forms a substantially insulating coating thereon and greatly retards transference of heat from the food storage compartment to refrigerant in the evaporator. To retard the transference of heat from the food storage compartment to the evaporator results in prolonged operations of the refrigerant liquefying and circulating unit and causes undue wear and strain on operating parts thereof as previously described. Provisions have heretofore been made to periodically and temporarily render the refrigerant liquefying and circulating unit inoperative automatically at predetermined timed intervals to permit the temperature of the evaporator to increase above its normal high temperature limit in order to melt or cause frost to be removed from the cooling surfaces of the evaporator. As previously explained this automatic and periodic defrosting of evaporators in prior apparatuses has occurred irrespective of the amount or thickness of frost on the evaporator. Consequently evaporators or prior refrigerating apparatuses were defrosted at predetermined timed intervals regardless of whether they needed to be defrosted or not. Thus if a defrosting period of prior apparatuses occurred at the same time that fast freezing of a substance contained in a tray and located in the freezing compartment of the evaporator was desired, the freezing operation of this substance was delayed even though the evaporator did not need to be defrosted. My invention has to do with providing means for periodically defrosting an evaporator of a refrigerating system at predetermined timed intervals and to cause such defrosting at such intervals only after the frost accumulation has attained a thickness on the evaporator sufficient to impede transfer of heat from food products of air in the storage compartment of the refrigerator or to cause prolonged and abnormal operating periods of the refrigerant liquefying and circulating unit.

An electrically operated clock or chronometric device generally designated by the numeral 40 is installed in any suitable location adjacent the evaporator 25 in the refrigerator cabinet 26 (see Fig. 1). This clock or chronometric device may be stationarily mounted in compartment 21 in a predetermined spaced relationship to the side wall of the evaporator 25. The clock or chronometric device includes a conventional synchronous electric motor (not shown) which is continuously operated by its being connected at all times with a source of electric energy. A switch is also associated with the clock or chronometric device and is normally maintained. in closed position and is connected in series relation in the electric circuit leading to the control switch 33 and motor 3|. "The electric circuit which is opened and closed by the control switch 33 for controlling operations of the motor 3| and consequently compressor 20 includes wire 4|, wire 42, the switch in the chronometric device 40, wire 43 contacts 44 and 45 of the control switch 33, wire 46 and 41 (see Fig. 1). The electric circuit leading to the synchronous motor in the chronometric device 48 includes wire 48, and wire 49 connected with wire 4|. The switch contained in the chronometric device 46 is normally closed and opening and closing of the contacts 44 and 45 of control switch 33 obviously makes or breaks the electric circuit to motor 3|. Thus changes in pressure in the gaseous refrigerant lines 29 and34, corresponding to changes in temperature of the evaporator of refrigerating system, causes the bellows 36 to actuate the movable contact 45 of switch 33 into and out of engagement with stationary contact 44 to cause cyclical operations of the motor 3| in response to demands placed on the refrigerating system.

Referring now to Figs. 2 to 'l inclusive it will be noted that the chronometrically operated timing device comprises a housing 55 located within the cover or enclosure of the device 40. Any suitable or well-known type of clockor timing device including a synchronous motor (not shown) may be located within the housing. 55 and may comprise a plurality of gears or the like for causing rotation of a shaft 56-which extends outwardlyof the housing 55 (see Figs. 6 and 7) at any desired or predetermined speed. Shaft 56 has a shoulder 51 formed thereon to provide a shank portion 58 which serves as a pivot point for an arm 59. The function and operation of arm 59 will be more fully described hereinafter. A second shoulder 6| formed on shank portion 58 of the shaft 56 provides a second shank portion 62. A shoulder 63 formed on shank portion 62 provides another shank portion 64 on shaft 56 which is squared in cross section for a purpose to be presently described. The remainder of shaft 56 extending outwardly from the shoulder and shank-portionsjust described is reduced in diameter and is threaded as at 66. After the arm 59 has been placed over the shank portion 58 of shaft 56 a member 61, having a cam portion 68 provided thereon, (see Figs. 2, 3, 4, and 6) is then positioned on the shank portion 62 of shaft 56. A disc 10 having a squared opening therein is then positioned upon the squared shank portion 64 of shaft 56. Another disc 1| is placed over disc 16 and the member 61, disc 10 and the disc 1| are then held in position upon shaft 56 by a nut 12 threaded upon the threads 66. Member 61 and disc 1| are prevented from being rotated relative to shaft 56 and relative to one another by the squared open-- ing in disc 10 receiving the squared portion 64 of the shaft 56 and by virtue of the provision of a finger 14, formed'on disc 1|, which passes through an elongated slot 15, provided in disc 10, and through an opening 16 formed in member 61 (see Fig. 7). Thus it is apparent that as shaft 56 is'rotated by the motor of the time or chronometric device, disposed within the housing 55, the parts just described will also be rotated. The chronometric device may be of a. design to cause the shaft 56 to be rotated a complete revolution in any predetermined number of hours or days according to the interval of the time desired between defrosting periods. The arrangement and association of the parts designated by the numerals 61, 18, 1| and 12 with the chronometric device 46 are such that they permit adjustment thereof relative to the device 40 to cause defrosting periods to be initiated at certain desired times. For example, these parts may be moved or adjusted relative to the shaft 56 of device 40 to cause a defrosting period to be initiated at twelve .oclock midnight instead of during the day when refrigeration is not desired to be interrupted.

Since my invention relates to a refrigerating system in which a chronometrically operated device is adapted to render the refrigerant liquefying and circulating unit of the system inoperative periodically but only when a predetermined amount or thickness of a layer of frost has accumulated on the evaporator some provision must be made to render the electric switch, associated with and adapted to be actuated by the chronometrically operated device, inefiective at a time when a defrosting period arrives unless the evaporator is coated with a certain predetermined layer of frost. Therefore, I associate a mechanism with the timing or chronometric device for operating a. feeler which controls or governs operation of an electrical switch adapted to be actuated by the device. The electric switch associated and adapted to be actuated by the chronometric device to break the electric circuit leading to control switch 33 of the refrigerating system includes a small. glass tube 19 having a quantity of mercury 80 sealed therein (see Figs. 3 and 4). The mercury 80 is'adapted to bridge a pair of contacts 8l'extending into the tube 19 and connected with the wires. 42 and 43. The mercury tube 19 is mounted within a plurality of arms 82 secured to or formed on a bracket 83. Bracket 83 includes apair of legs 84. A shaft or stud 85 passes through the legs 94 and through a support 86, secured to the top wall of housing 55 (see Fig. 6), to pivotally mount the bracket83 thereon. One of the legs 84 provided on bracket 83 extends downwardly a greater distance than the other leg and has a slot 81 (see Figs. 3 and 4) formed therein. The slot 81 receives a pin" 88 secured to the upper end of arm 59 to cause movement of bracket 83 to actuate the mercury switch about its pivot point 85 upon movement of. arm 59. A link 9| is connected with.arm 59 by a loose connection 92 and link 9| is connected with another arm 93 by a loose connection 94. The arm 93 extends upwardly and includes a. hook portion 96 which carries a feeler 91. The feeler 91 is loosely or pivotally mounted on hook portion 96 by screw 98 so as to permit the flat outer surface thereof to engage frost accumulated ,on the wall of the evaporator 25 which wall is fragmentarily represented in Figs. 2, 3, 4 and of the drawings. It will be noted that feeler 91 and end or hook portion 96 of arm 93 may extend or may be moved outwardly of the casing or housing of the device 40 through "an opening 99 provided therein (see Figs. 1 and 2).

An arm |6| is pivotally mounted as at I02 upon a wall of the housing or box 55, which contains the chronometric device or mechanism, and this arm IOI has a pin or shaft I03 extending therethrough and through the arm 93 to lock arm IM and arm 93 together (see Fig. 5). The pin or shaft I03 also carries a roller I04 in alignment with the edges of the member 61 so as to be engaged by the cam 68. The pin or shaft I03 further serves as a fulcrum point for movement of the arm 93 relative to arm IOI as will be more fully described hereinafter. An indicator finger I05 is secured in any suitable manner to housing 55 and has a pointer registering with numerals or the like provided on disc 10. A spring I01 has its one end secured to the movable pin 98, carried by the arm 59, and has its opposite end secured to a peg or pin I08 stationarily mounted on and extending from a wall of the housing 55. The screw or stud 94 which connects link 9| with arm 93 serves as a stop for arm 93, link 9| and arm 59 since the spring is under tension at all times thereby tending to maintain the link, arms, etc., of the mechanism described in a neutral position as shown in Fig. 2 so that roller I04 always engages the edge surface of member 61 which has the cam 68 formed thereon. It is apparent, that since roller I04 is always held in engagement with member 61, the cam 68 when rotated by the chronometric device, moves into engagement with roller I04 and arms 93 and IM willbe moved to the left as viewed in Fig. 3. This movement causes link 9I to move arm 59 in a clockwise direction about its pivot point, shaft 56, a short distance which is insufilcient to trip thev mercury switch. The movement just described occurs only when there is no or a very thin layer of frost on the walls of the evaporator 25, and is illustrated in Fig. 3 of the drawings to show that the chronometrically operated device is normally ineifective for rendering the refrigerant liquefying and circulating unit inoperative to cause defrosting of the evaporator.

However, should the outward movement of arm 93 to the left as viewed in the drawings, be resisted or prevented, such for example, as by a layer of frost III as shown in Fig. 4, the portion of arm 93 located below the pin I03 and roller I04 will be caused to move in a clockwise direction about the fulcrum pin I03 when the cam 69 engages or moves the roller I04. As shown in Fig. 4 the feeler 91, attached to the upper end 96 of arm 93, has engaged the abnormal layer of frost III on the wall of the evaporator 25 and has caused movement of arm 93 relative to arm IM and has caused link 9| and arm 59 to be moved a greater distance to the left than normally occurs. This abnormal movement of these arms etc.,-is sufficient to tilt bracket 83 beyond the dead center of its pivot point 95 relative to the pin 89 to render the mercury switch and consequently the chronometric device 40 effective for initiating a defrosting period. Tilting of the mercury switch, associated with bracket 83, as described causes the mercury to flow tothe end of the tube 19, opposite the end thereof in which the contacts BI are disposed, and thus breaks the electric circuit through wires 42 and 43. Wires 42 and 43 being connected in series with the source of electric current leading to the control switch 33 obviously render the regrigerant liquefying and circulating unit inoperative. The duration of the defrosting or inoperative period of the refrigerant liquefying and circulating unit may be determined by the size of the cam 68 in accordance with the time required to cause a complete revolution of the member 61. The feeler member 91 is preferably constructed of a poor heat conducting material such for example as bakelite or hard rubber so as to prevent its rapid entrance into the layer of frost or ice III on the evaporator 25 as the case would be if the feeler 91 was of a good heat conducting material. Therefore the feeler member ,91 does not melt the frost or ice III on evaporator 25 with which it contacts any faster than melting of the frost occurs over other portions of the evaporator. In fact, it has been found that the feeler 91 blocks off or isolates that portion of the layer of frost or ice with which it contacts from the relatively warm air circulating within the food storage compartment 21 of the cabinet 26. This, therefore, insures that all portions of the evaporator will be defrosted prior to the time the frost or ice under the feeler 91 melts and prior to the time when the cam 68 moves away from the roller I04 to cause the refrigerating system to again become operative. After the desired length of time allotted for causing defrosting of ice III from walls of evaporator 25 has elapsed, the continuous operation of the chronometric device moves cam 68 away from and out of engagement with the roller I04. Spring I01 then moves arm 59 in a counter-clockwise direction about its pivot thus moving link 9|, arm 93, and arm IN to the right or into a position as shown in Fig. 2. This movement causes the head of the pivot pin 94 to engage the edge of arm IN to prevent further movement of arm 93 to the right and to cause roller I04 to engage the cylindrical edge surface of member 61. This latter movement, created by the spring I01, also causes the mercury switch to be tilted off center or to the right as shown in Fig. 2, relative to its position shown in Fig. 4, to cause the mercury 80 to again bridge the contacts 8| for completing the electric circuit to the control switch 33.

After the chronometric device 40 has caused elements associated therewith to move in the position above described and shown in Fig. 2, the regrigerant liquefying and circulating unit continues in its cycles of operation under the control of switch 33. The cam 68 associated with and rotated by the chronometric device may make one or more complete revolutions, in an endeavor to initiate defrosting periods, before a layer of frost or ice of sufficient thickness has accumulated on the walls of the evaporator 25 to render the device operative to cause defrosting of the evaporator. When the cam 68 has made a complete revolution to actuate roller I04, arm 93, arm IM and feeler 91 from the positions shown in Fig. 2 of drawings into the position shown in Fig. '3 and when there is a very thin layer of frost only present on the walls of the evaporator 25 the feeler 91 is permitted to be moved to the left or toward the evaporator 25 without being stopped by the ice formation. This movement does not cause link 9|: and arm 59 to move a sufficient distance to actuate the mercury switch of the device and therefore the chronometric device 40 is maintained ineffective for causing defrosting of the evaporator until a predetermined thickness of frost or ice; has formed on walls of the evaporator. When movement of the feeler 91 of the mechanism toward a wall of the evaporator 25 is blocked or prevented by a layer of frost or ice on a wall of the evaporator as shown in Fig. 1 and as previously described, the mechanism functions to tilt the mercury switch and cause the electric circuit leading to the control switch 33 to be opened. 1

It will be apparent from the foregoing that I have provided an improved refrigerating system of the type in which a chronometrically operated means is employed to cause the evaporator of the system to be periodically defrosted at predetermined intervals of time but which is normally maintained ineffective and rendered effective only after a predetermined amount or thickness of frost has accumulated on walls of the evaporator. My improved system thereby eliminates the occurrence of defrosting periods, that are automatically initiated at predeterminedintervals of time, unless a certain amount or thickness of frost has accumulated on the walls of the evaporator thus insuring defrosting of the evaporator only when necessary. This feature renders my refrigerating apparatus more eflicient and more desirable than a' system in which there is a means which causes periodical defrosting of the evaporator at timed intervals irrespective of th condition of the evaporator.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. Refrigerating apparatus including a cooling element disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, means connected with said cooling element and adapted to circulate a re-,. frigerant medium therethrough, means forconl trolling the operation of said refrigerant circulating means to normally maintain said cooling element between predetermined temperature limits, chronometrically operated means for causing the temperature of said cooling element to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normallyinefiective, and means for rendering said chronometrically operated means eifective after a predetermined amount of frost has accumulated on the cooling, surfaces of said cooling element.

2. Refrigerating apparatus including an evaporator disposed in a compartment to be refrigerated and having -cooling surfaces upon which frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, means for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to. normally maintain the temperature thereof between predetermined limits, chrdnometrically operated means for causing the temperature of said evaporator to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, and means for rendering said chronometrically operated means effective after a predetermined amount of frbst has accumulated on the cooling surfaces ofsaid evaporator.-

3. Refrigerating apparatus including a cooling element disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, means connected with said cooling element and adapted to circulate a refrigerant medium therethrough, means for con-- trolling the operation of said refrigerant circulating means to normally maintain said cooling element between predetermined temperature limits, chronometrically operated means for determined limits,

causing the temperature of said cooling element to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a member actuated by operation of said chronometrically operated means into close proximity to said cooling element, and said member being adapted after a predetermined thickness of frost has accumulated on the cooling element to engage the frost and cause said chronometrically operated means to be rendered effective.

4. Refrigerating apparatus including a cooling element disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, means connected with said cooling element and adapted to circulate a refrigerant medium therethrough, means for controlling the operation of said refrigerant circulating means to normally maintain said cooling element between predetermined temperature limits, chronometrically operated means for causing the temperature of said cooling element to increase, temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a cam actuated by operation of said chronometrically operated means, and an arm associated with said cam and movable thereby into close proximity to said cooling element, said arm being adapted after a predetermined thickness of frost has accumulated on the cooling element to engage the frost and cause said chronometrically operated means to be rendered effective.

5. Refrigerating apparatus including an evaporator disposed in a compartment-to be refrigerated and having cooling surfaces upon which frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, means for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to normally maintain the temperature thereof between predetermined limits, chronometrically operated means for causing the temperature of said evaperated and having cooling surfaces upon which go frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, means for controlling the operation of said unit to cyclically circulate'a refrigerant medium through said evaporator to normally maintain the temperature thereof between prechronometrlcally operated means for causing the temperature of said evaporator to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a cam actuated by operation of said chronometrically operated means, and an arm associated with said cam and movable thereby into close proximity to said evaporator,

said arm being adapted after a predetermined thickneses of frost has accumulated on the evaporator to engage the frost and cause said chronometrically operated means to be rendered effective.

'7. Refrigerating apparatus including an evaporator disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, ,a refrigerant liquefying and circulating unit operatively connected with said evaporator, means normally effective for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to maintain the temperature thereof between predetermined limits, a switch for rendering said normally effective control means ineffective to cause the temperature of said evaporator to increase temporarily above the normal predetermined high temperature limit thereof, chronometrically operated means for actuating said switch, said chronometrically operated means being normally ineffective, and means for rendering said chronometrically operated means effective after a predetermined amount of frost has accumulated on the cooling surfaces of said evaporator.

8. Refrigerating apparatus including an evaporator disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, an electrical circuit and a normally effective switch interposed therein for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to maintain the temperature thereof between predetermined limits, a second switch interposed in series relation with said normally effective control switch in said electrical circuit for rendering said control switch ineffective to cause the temperature of said evaporator to increase temporarily above the normal predeter mined high temperature limit thereof, chronometrically operated means for actuating said second named switch, said chronometrically operated means being normally ineffective, and means for rendering said chronometrically operated means effective after a predetermined amount of frost has accumulated on the cooling surfaces of said evaporator.

9. Refrigerating apparatus including a cooling element disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, means connected with said cooling element and adapted to circulate a refrigerant medium therethrough, means ror controlling the operation of said refrigerant circulating means to normally maintain said cooling element between predetermined temperature limits, chronometrically operated means for causing the temperature of said cooling element to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a member actuated by operation of said chronometrically operated means into close proximity to said cooling element, and said member being adapted, after a predetermined thickness of frost has accumulated on the cooling element, to move in a plane substantially at right angles to the exterior of the layer of frost into engagement with the frost to cause said chronometrically operated means to be rendered effective.

10. Refrigerating apparatus including a cooling element disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, means connected with said cooling element and adapted to circulate a refrigerant medium therethrough, means for controlling the operation of said refrigerant circulating means to normally maintain said cooling element between predetermined temperature limits, chronometrically operated means for causing the temperature of said cooling element to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally inefiective, a cam actuated by. operation of said chronometrically operated means, and an arm associated with said cam and movable thereby into close proximity to said cooling element, said arm being adapted, after a predetermined thickness of frost has accumulated on the cooling element, to move in a plane substantially at right angles to the extension of the layer of frost into engagement with the frost to cause said chronometrically operated means to be rendered effective.

11. Refrigerating apparatus including an evaporator disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, means for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to normally maintain the temperature thereof between predetermined limits, chronometrically operated means for causing the temperature of said evaporator to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a member actuated by operation of said chronometrically operated means into close proximity to said evaporator, and said member being adapted, after a predetermined thickness of frost has accumulated on the evaporator, to move in a plane substantially at right angles to the extension of the layer of frost into engagement with the frost to cause said chronometrically operated means to be rendered effective.

12. Refrigerating apparatus including an evaporator disposed in a compartment to be refrigerated and having cooling surfaces upon which frost accumulates, a refrigerant liquefying and circulating unit operatively connected with said evaporator, means for controlling the operation of said unit to cyclically circulate a refrigerant medium through said evaporator to normally maintain the temperature thereof between predetermined limits, chronometrically operated means for causing the temperature of said evaporator to increase temporarily above the normal predetermined high temperature limit thereof, said chronometrically operated means being normally ineffective, a cam actuated by operation of said chronometrically operated means, and an arm associated with said cam and movable thereby into close proximity to said evaporator, said arm being adapted, after a predetermined thickness of frost has accumulated on the evaporator, to move in a plane substantially at right angles to the extension of the layer of frost into engagement with the frost to cause said chronometrically operated means to be rendered effective.

13. A refrigerating system including an insulated cabinet having an evaporator located therein, means for automatically controlling said system to cause said evaporator to produce a refrigerating effect, said evaporator having a cooling surface upon which frost accumulates, a device for causing said evaporator to defrost, a chronometrically controlled means .for operating said device, said device being normally ineffective for defrosting said evaporator said device including a member actuated at prede- 10 termined timed intervals by operation. of said device into close proximity to said cooling surface of said evaporator, and said member being adapted, after a. predetermined thickness of frost has accumulated on said cooling surface of said evaporator, to movein a plane substantially at right angles to the extension of the layer of frost into engagement with the frost to cause said defrosting device to be rendered effective.

HARRY B. HULL.

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