US2780925A - Refrigerating apparatus having automatic defrost - Google Patents

Description

' Feb. 12 1957 T. A. MCGREW ET A 2,780,925

REFRIGERATING APPARATUS HAVING AUTOMATIC DEFROST Filed Nov. 21,1955 2 Sheets-Sheet 2 FIG. 3

/ 63b 5 rasa J I 2 2 2 1/ I. I 4'6 /l l l l INVENTORS. THOMAS A. MC GREW & ROBERT A. WACHTER TH EIR ATTORNEY United States Patent 6 REFRIGERATING APPARATUS HAVING AUTOMATEC DEFROST Thomas A. McGrew, Fern Creek, Ky., and Robert A.

Wachter, Glens Falls, N. Y., assignors to General Electric Company, a corporation of New York Application November 21, 1955, Serial No. 547,904

9 Claims. (Cl. 62-4) This invention relates to refrigerating apparatus and more particularly to food freezers provided with simple and effective means for restricting frost collection to a predetermined portion of the evaporating or chilling unit from which the frost is periodically and automatically removed.

Refrigerators of the type in which food stuffs are stored for extended periods of time at temperatures below freezing are usually provided with a plurality of evaporating or chilling units disposed throughout the refrigerator food storage compartment. One of these evaporators is generally located in the top portion of the storage compartment and others in heat exchange relationship with the various spaced shelves within the cabinet. When the compartment door is opened, cold air spills out the bottom and warm moist air enters the compartment at the top. Thus frost from the moist air tends to deposit most heavily on the refrigerated top portions of the compartment and uppermost refrigerated shelves. To limit the area requiring frequent defrosting, special means have been taken to maintain the refrigerated compartment top at a significantly lower temperature, using an evaporator which operates at temperatures below the remaining evaporators. Frost and moisture in the air within the compartment will migrate to this colder evaporator where they are deposited and with the frost accumulation restricted to one evaporator, the remaining evaporators remain relatively free of frost enabling the apparatus to operate more efliciently.

The proximity of the low temperature evaporator unit to the upper wall of the food storage compartment creates low temperatures particularly in the gasket region and outer portions of the refrigerator cabinet causing the condensation of moisture from the outside air on these surfaces of the cabinet. In addition, the portions of the breaker strip within the interior of the compartment adjacent the colder evaporator also become covered with moisture which either drips into the access opening when the door is open or forms an excessive frost or ice layer on the strip.

Accordingly, it is an object of our invention to provide a new and improved freezer construction particularly adapted to prevent undesired condensation on or adjacent to the breaker strip along the upper edge of the access opening to the cabinet.

It is another object of our invention to provide an improved arrangement for removing moisture from the air within the food storage compartment of refrigerating apparatus and to efficiently dispose of the moisture so removed through conduits from which accumulated frost is first removed.

It is a further object of our invention to provide a novel arrangement for automatically initiating defrosting of refrigerating apparatus in accordance with a predetermined period of compressor operation which includes a complete shut down of the refrigeration system during defrosting and terminating the defrosting by inice 2 dependent temperature responsive means when the accumulated frost has been removed.

It is a still further object of our invention to provide a cabinet structure for refrigerating apparatus which minimizes the condensation of moisture from the outside air on its external surfaces, and on the interior portions of the breaker strips when the door is opened.

It is still another object of our invention to provide a simple and efiicient arrangement for effecting accumulation of substantially all frost on one of a plurality of units so that the remaining units, breaker strip, and the food storage compartment walls of a low-temperature refrigerating apparatus operate substantially frost and condensation free.

In carrying out our invention, we provide refrigerating apparatus having an insulated cabinet for the storage of food stuffs at below freezing temperatures over prolonged periods of time. A plurality of evaporator units are arranged within the food storage compartment, one of which being maintained at a lower temperature than the remaining evaporators and is partially positioned in a recess in top wall of the compartment. Insulation and a breaker strip of novel configuration are provided to partially form the recess and thermally isolate this upper evaporator from the remaining cabinet walls to provide a compartment construction that permits the moist air in the compartment to migrate to the recess for contact with this colder evaporator. In a pre ferred form of the invention, this colder evaporator and its associated moisture draining means are periodically cleared of frost by auxiliary heating means which are energized after a predetermined period of compressor operation accompanied by a simultaneous shutdown of the refrigerating system, and ducts within the refrigerated cabinet conduit the defrost water to the outside of the cabinet where it is disposed of by evaporation.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and its mode of operation may be best understood by reference to the following description taken in conjunction with the accompanying drawing in which:

Fig. l is a fragmentary side view partially in section of a refrigerator cabinet including our invention;

Fig. 2 is a schematic diagram of the timing arrangement for our invention.

Fig. 3 is a fragmentary view partially in section taken substantially along line 33 of Fig. 1; and

Fig. 4 is a diagrammatic view of the refrigeration system employed in the arrangement of our invention.

Referring now to Fig. l, we have illustrated therein a refrigerator cabinet which includes an outer metal wall 1 and an inner metal wall or liner 2, the space between the walls being filled with suitable heat insulating material 3. The walls are formed to provide a door opening 4 at the front of the cabinet, and the inner liner 2 defines a food storage compartment 5 within the cabinet. The door opening 4 provides access to that compartment. The opening 4 may be closed by any suitable insulated door (not shown).

The storage compartment 5 is refrigerated by means of a suitable mechanical refrigeration system which may be seen best by reference to Fig. 4, and is preferably of the type employed when it is desired to maintain the foodstuffs in the storage compartment 5 at tem' peratures somewhat below freezing in order to preserve the food stored therein for prolonged periods of time. The refrigeration system comprises a compressor 6, a condenser 7 connected by an expander or capillary tube 8 to a plurality of serially connected evaporators 9 through 12. Evaporators 9 through 11 are formed as a part of shelves 13 through 15 respectively which are spaced apart in vertical overlying relationship within the food storage compartment of my refrigerator. One of the shelves 13 and its associated evaporator coil 9 is shown in Fig. l suitably supported within the compartment 5. Evaporator 12 forms a part of the bottom wall 16 of the compartment 5. As will be understood in Fig. 4, these evaporators are serially connected and spaced through the compartment 5 for uniform cooling thereof.

Evaporator 12 is appropriately connected by tubing through a weighted valve 17 to an evaporator coil 18 which is arranged adjacent the top of compartment 5 and slopes downwardly to the compartment rear wall as shown in Fig. 1. The weighted valve 17 may be of any type generally known to be used in refrigeration apparatus where it is desired to create a selected pressure drop in a refrigeration circuit Our valve 17 creates a pressure drop and therefore a temper'ature drop in the refrigerant so that the uppcrcvaporator 18 will operate at a temperature below that of the evaporators 9 through 12. By operating the upper evaporator 18 at this reduced temperature, the warm moist air entering the compartment when the door is opened will deposit its moisture in the form of frost on the underside of a refrigerated plate 24 arranged beneath the evaporator 18 and therefore substantially eliminating the formation of frost on the remaining evaporators 9 through 12.

The'evaporator 18 then discharges the refrigerant into a liquid accumulator 19. A closed circuit is established in the refrigeration system by connecting this accumulator 19 to the compressor 6 with appropriate suction line tubing in heat exchange relationship-to the capillary tube '8.

Referring now to Fig. l, the space between the inner wall 2 and outer wall 1 of the cabinet along the upper horizontal portion of the door opening 4 is closed or bridged by a U-shaped breaker strip 20. The remaining portions of the door opening are also defined by breaker strips 21 but they may be of any desired configuration as shown in Fig. 3 so as to close the space between wall 1 and wall 2. This breaker strip 20 is connected by suitable means, such as clips, at the upper end of its forward extension 20a to a flange 1a on wall 1. The breaker strip 20 is also provided with a substantially vertical rear extension 20b having a bent-over portion 20c, 20b and 20c together forming an L-shaped recess or pocket 22 at the top front of compartment 5. Suitably connected to the breaker strip portion 20c and to the top of the vertical rear wall 2a of the inner liner 2 is a bridging member 23 formed of insulating material and having an upwardly slanting front portion 23a and perforations 23b.

This vertical wall 2:; is preferably deep drawn as shown best in Fig. 3 to provide a channel for the circulation of air in the compartment upwardly to the compartment top around the rear of the shelves 13 through 15. A fiat I118- tallic plate 24 having upstanding rn ar'ginal flanges 25 a, 2512, 25c, 25d is suitably mountedby means such as brackets 26 and screws 27 tothe slanted portion 23a of the insulated bridging member 23. This plate 24 is arranged to accommodate the low temperature evaporator 18 which lies across the plate in a plurality of Zig-zag turns as shown in Fig. 3. Theplate is mounted at its'lower It is well-known that the phenomena of sweating 0e.- curs when the temperature of the outer cabinet wall falls below the dew point of the air surrounding the wall causing moisture to condense on the cold wall surface. In addition, the recess 22 formed by the breaker strip extension 20b 'and bent-over portion 200 produces a natural air pocket with the cold plate 24 so that the air circulation along the vertical portion 20b of the strip is limited reducing the movement of moisture laden air in the recess 22 and the subsequent accumulattion of frost. It will also be noted that the forward end of the low temperature evaporator coil 18 is located a short distance back from the forward flange 25:: on the cold plate 24 providing a temperature gradient from the coil to the breaker strip 20 and further reducing the possibility of sweating in the gasket region 31.

We have provided a perforated, insulated bridging member 23 at the topof the compartment 5 rather than a metal wall to thermally isolate the plate 24 and coil 18 from the remaining metal portion of the liner 2. This wall 23 additionally serves to retain the insulation 3 in place and any moisture in the insulation will migrate through its perforations 23b to the cold plate 24.

In order to provide a path for the water formed when the plate 24 and coil 13 are defrosted, the rear turns of coil 18 are turned up as at 32 to permit the water to run down to the rear end of the slanted cold plate 24. The cold plate 24 is formed with such a surface on its underside that when the frost, which has collected thereupon, melts it will flow to the back of the plate 24 and into the trough 29, without dripping into the compartment 5.

Referring now to Fig. 3, the trough 29 therefore is arranged to receive the water flowing along the top and underside of plate 24. The water in the plate top flows through the rear corner openings 33a and 33b in the plate 24. In order to receive the water flowing through the trough 29, which is tilted to one side of the cabinet, we provide a metallic drain tube 34 to which the trough slopes which has an upwardly extending scoop 35. The tube is disposed within the insulation 3 and extends through the liner wall 2a such that the sloped trough discharges into the scoop 35. The drain tube 34 is received within a section of insulated tubing 36 suitably mounted to the outer cabinet wall 1 by means such as plate 37 appropriately secured on the cabinet exterior. The tube 36 is 'cornposed of an insulating material such as plastic to provide a temperature barrier so that the outer wall 1 will not have moisture condensing on its surface. Withoutthe insulated portion on the tube the temperature at the outer wall would be so low that sweating would occur on the wall surface. The tubing 36 extends without the refrigerator cabinet beyond the outer wall 1 and is'connected at its outer end to a flexible drain tube 38 composed of a material such as rubber which depends downwardly into a'liquid trough or reservoir 39 suspended by a hooked portion 44? on the condenser 7. The

' trough 39 extends substantially the width ofthe cohrear end to the vertical liner wall 2 a by a plurality or- V spaced insulated pins 28 extending through the linewall 2a and the rear flange 25 oflthe plate. Also supported on the P111828 is an L-sh'apedtrough'29 suit ablyinsulated from the plate rear flange 25a by insulated washers 30 and sloped to one side of the cabinet.

It can be seen that the -U-shaped breaker strip 20 'is the gasket region creating what is-knovvn as sweating.

denser. The plastic tubing 36 is formed with a restricted end'opening 41 as shown in Fig. l which cooperates with the rubber tubing 38 to form a water seal to prevent the entrance of outside air into the compartment 5. This water trap is preferably arranged as shown so'that any abnormal pressure arising from slamming'the door of the cabinet will not blow outthe water destroyingthe seal.

In order to protect the cold plate 24 and to prevent the jamming up of food packages against it where they could warm up during defrosting, we provide a package guard 42 formed of wire and arranged belowthe plate '24 asshown in Fig. 1. The package guard is supported at its forward end on a plurality of hooks 43 arranged, on

the breaker strip 26 and has rear wire portions extending'through openings appropriately provided in the "corn-f pattin'ent rearwall 2a. The guard is'so locateddhat'air' circulation around the cold plate 24 is permitted and there is an unobstructed defrost water run-off down the sloping underside of the cold plate 24.

I We have therefore provided a low-temperature evaporator coil and plate in the top of a low temperature, food storage compartment of refrigerating apparatus to which moisture laden air in the compartment will migrate whereupon the moisture deposits on the coil and plate in the form of frost. We have also provided means to dispose of the water resulting from a melting of the accumulation of frost.

As shown in Fig. 2, we have further provided a timed heating arrangement for melting and disposing of the frost accumulated on the surfaces of coil 18 and plate 24 which comprises a length of an appropriately placed resistance type heater. The heater is formed of 3 resistance units 44,45, 46 of varying resistance serially connected andenergized by suitable electrical means.

Referring now to Fig. 1, the heater first passes along the trough 29 with resistance unit 44 in intimate contact with the trough. From the trough, the heater is then placed in contact with the metallic drain tube 34 and scoop portion 35 using a resistance unit 45. From resistance unit 45, a connection is made to a third resistance element 46 which is coiled in serpentine configuration between the passes of the refrigerant evaporator coil 18 in intimate thermal relationship with the cold plate 24 as shown in Fig. 3. formed of different ohmic values so that when the ends of the heating wire are connected to a current source, resistance 45 heats up the fastest, followed by unit 44, and finally heating unit 46. Thus the unit with the highest wattage concentration is unit 45, the intermediate unit is 44 and the unit of lowest wattage concentration is unit .46. This difference in wattage concentration is so selected that frost on the metallic tube 34 and scoop 35 ismelted first then the frost on trough 29 and finally the frost on cold plate 24. Thus water draining from the plate 24 does not encounter a plugged drain trough. or drain tube from which the ice has not had time to melt even though the ice has melted from the cold plate 24.

Referring again to Fig. 2, we have shown a motor driven, clock timer 47 connected in parallel with the motor of compressor 6 both of which are connected through switching means to a pair of supply conductors 48, 49. One side of the timer and compressor motor is connected through a cycling control 50, which is responsive to a predetermined high temperature in the storage compartment of the refrigerator, to supply conductor 48 to connect the timer 47 and compressor 6 into the power circuit. After a predetermined low temperature is reached, in the compartment 5 the cycling control 50 acts to open the circuit to the timer and compressor deactivating the refrigeration apparatus. The cycling control may be of any well-known type to accomplish this desired type of control. As the refrigeration apparatus of which our invention is a part is of the type in which the temperature in the storage compartment 5 is maintained below freezing continuously, the cycling control 50 therefore operates within a temperature range below that of freezing.

As the timer 47 is connected in parallel with the motor of compressor 6, the timer rotates only when the compressor 6 is operating. A cam 51 is mounted on the timer shaft and is therefore rotated by the timer only when the compressor 6 is in operation. The cam 51 is associated with contact strips 52, 53, and 54 supported through a wall of the timer housing 55 and maintained in spaced parallel relationship by a spacer 56. Contact strip 52 is provided on the upper side of its free end with a contact 57 and has a cam follower 58 directly beneath its underside which cooperates with the timer cam 51. The contact strip 53 is provided with a double contact 59 fixed to a point on the strip intermediate its free end and spacer 56. Contact strip 54 is also provided with a These resistances 44, 45, and 46 are contact 60 on the underside of its free end. It will be noted that the three resistance heating units 44, 45, 46 are connected serially with one end connected to the supply conductor 48 and the other end to the fixed end of contact strip 54. Contacts 57 and 59 are normally in circuit closing contact establishing a connection from the power supply conductor 49 to the timer 47 and the motor of compressor 6. Thus the timer and compressor motor will run if the cycling control closes to connect the other side of the timer and compressor motor to supply conductor 48.

A gas filled flexible bellows 61 located within the housing is connected by a capillary tube 62 to a temperature responsive bulb 63 positioned on the cold plate 24 as shown in Fig. 1. A lever 64 pivotably attached to pin 65 appropriately mounted on the housing 55 is maintained in contact at one end with the bellows 61 by a spring 66 positioned within a recess 67 within the housing wall. tached to the end of the pivotable lever 64 opposite the bellows, ina downward and outward direction.

In theoper-ation of the control of Fig. 2, whenever the cycling control 50 senses the predetermined high temperature within the storage compartment 5, its contacts close completing a connection from supply conductor 48 to one side of the timer 47 and the motor of compressor 6. The circuit is completed from the other side of the timer and compressor motor through contacts 57 and 59 on contact strips 52 and 53 respectively to the supply conductor 49. The compressor and the timer therefore run concurrently.

As our defrosting means is arranged to operate after a predetermined period of compressor operation, the cam 51, which is rotated by the timer 47, causes the con: tact strips 52 and 53 to rise gradually until the free end of strip 53 snaps over the offset on the retainer'68. Contacts 59 and on strips 53 and 54 respectively are still spaced apart at this time due to the spreading action of the spacer 56. As the cam 51 continues to revolve the cam follower 58 will drop off the high point of the cam which allows contacts 57 to snap away from contact 59 since the contact strip 53 is maintained in the raised position by the offset on the retainer 68 which engages the free end of the strip. At the same time contact 60 returns to its normal horizontal position and snaps into contact making engagement with contact 59.

At this time, the circuit to the timer and compressor motor is interrupted and they are tie-activated by the separation of contacts 57 and 59. A circuit is now completed from supply conductor 49 through strip 53 through contacts 59, 60, through strip 54 to the defrost heaters 44, 45, 46 and through the defrost heaters to supply conductor 48.

As discussed above, since heaters 44 through 46 are of different wattage concentrations, different periods of time will be required to warm up and melt the frost on the part of the apparatus associated with each heater. Thus heater 45 heats up the drain tube 34 and scoop 35 first, followed by the heater 44 which heats up the drain trough 29, and finally heater 46 warms up to melt the frost from the plate 24 and coil 18.

When the plate 24 reaches a predetermined temperature which is indicative of the substantially complete melting and draining of frost from its surfaces, this relatively high temperature sensed by the bulb 63 causes the bellows 61 to expand. Expansion of the bellows pivots the lever 64 in a counterclockwise direction moving the retainer 68 upwardly and to the right against the action of the spring 66. This movement of the retainer 68 eventually releases the free end of contact strip 53 off the retainer offset, separating contacts 59 and 60 thereby opening the circuit to the defrost heaters 44, 45, 46. Contacts 57 and 59 engage and permit energizing of the compressor and timer as before during the periods called for during normal operation by the cycling control 50.

The spring 66 biases a retainer 68, suitably at-' As the frost melts. from the cold plate 2'4, evaporator 18, the trough 29 and the drain tube 34, the resulting water beginning at the plate 24 and evaporator 18 flows through the trough 29 to one side of the cabinet and into the scoop 35 of the tube 34. The water continues on through tube 36 in the cabinet wall structure and out of the refrigerator cabinet through the rubber tubing 38 into the reservoir 39. Since the reservoir 39 is in heat transfer relationship with the hot condenser 7, primarily due to its hooked portion 40, this defrost water warms up and subsequently evaporates being carried away by the outside air. Thus the defrost wa'teris conveniently and completely disposed of from the inside compartment of the refrigerator cabinet.

It will be noted, that the timing arrangement totalizes the periods of operation of the compressor and after a predetermined total period automatically initiates the de frost heaters while deactivating both the timer and compressor. It is well-known in the refrigeration art that the period of compressor operation is directly proportional to the accumulation of frost on the evaporator coil since it is indicative of the number of door openings, or of high ambient temperatures with its attendant possible high absolute humidity and our arrangement takes full advantage of this phenomenon. Furthermore, the compressor and timer and consequently the refrigeration system of our apparatus is not restored to operation until all of the accumulated frost has been removed from the evaporator and other surfaces.

This results in an accurate, thorough, and highly edic ient defrost arrangement in which there is a minimum of shutdowns for the apparatus which are reasonably short in duration so that it is possible to maintain at all times the desired low temperature in the food storage compartment.

We have also incorporated features in our invention whicheliminate the condensation of moisture on the external cabinet surfaces of the refrigerator which often result when an extremelylow temperature prevails in -the food storage compartment.

While in accordance with the patent statutes we have described what at present is considered to be the preferred embodiment of our invention it should be obvious to those skilled in the art that various changes and modifications may be made therein without departingfrom our invention, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of ourinvcntion.

What we claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a refrigerating apparatus, a cabinet comprising inner and outer spaced-apart casings with thermal llJSUlflr tion disposedbetween said casings, said-inner casing defining a food storage compartment, an insulating breaker strip connecting together the edges of said casings and defining an opening for said compartment, a door for closing said opening, said breaker strip being of substantially U-shapedconfiguration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top wall of'said storage compartment a recessed area, aplurality of serially connected, vertically spaced evaporators Within said compartment with the upper evaporator extending across said compartment top inner wall and into said recess.

2. 111 a'refrigerating apparatus, a cabinet comprising an inner and outer, spaced apart easing with thermal insulation disposed betweensaid casings, said inner casing defining a'food storage compartment, an insulating breaker stripconnectingtogether the edges of said casings and defining an opening for said compartment, a door for closing said opening, a foramin'ous insulating inner top wall for said compartment, said breaker strip being of substantially U-shaped configuration along the top'ofsaid opening and having an L-shaped rear :portion extending upwardly to form with said wall a recess, a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment top and into said recess.

3. In a refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal in sulation disposed between said casings, said inner casing defining a food storage compartment, an insulating breaker strip connecting together the edges of said casing and defining an opening for said compartment, 2. door for closing said opening, said breaker strip being of substan-. tially U-shaped configuration along the top of said opening and having a'substantially L-shaped rear end extending upwardly and forming with the top wall of said storage compartment a recess, a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment adjacent said top wall in serpentine configuration and having one side'e xtending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said'upper evaporator arranged to operate at a lower temperature than said remaining evaporators to cause frost to migrate to said upper evaporator only.

4. In a refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining a food storage compartment, an insulating breaker strip connectingtogether the edges of said casings and def ning an opening for said compartment, a door for closing said opening, a foraminous, insulating, top wall for said compartment, said breaker strip being of substantially U-jshaped configuration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with said compartment top wall 'a recess, ,a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending in serpentine configuration across said compartment and sloped rearwardly adjacent said for aminous insulating top wall, whereby said evaporator'is thermally isolated from the remaining portions of said inner casing, said evaporator having one side extending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said upper evaporator arranged to operate at a lower tempera ture than said remaining evaporators to cause frost to migrate to said upper evaporator only.

5. .In a refrigerating apparatus, a cabinet comprising an .inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining afood storage compartment, an insulating breaker :strip connecting together the edges of said casings and defining an opening for said compartment, a door for 6105-. ing said openings, said strip being of substantially U- shaped configuration and extending along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top vwall of said storage compartment a recess, a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment adjacent said top wall in serpentine configuration and sloped rearwardly, said upper evaporator having-one side extending within the space defined by said recess, a metallic plate arranged below and attached to saro upper evaporator, said upper evaporator arranged to be operated at a lower temperature than said remaining oratoronly, means to defrost said upper evaporator after evaporators to cause frost to migrate to said upper evapa predetermined period, and means to drain said defrost liquid from said refrigerator cabinet.

'6. In a'refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining'alfood storage compartment, an'insulating breaker defining an opening for said compartment, a door for closing said opening, said strip being of substantially U- shaped configuration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top wall of said storage compartment a recess, a plurality of serially connected vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment adjacent said top wall in serpentine configuration and sloping rearwardly, said upper evaporator having one side extending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said upper evaporator arranged to operate at a lower temperature than said remaining evaporators to cause frost to migrate to said upper evaporator only, and said compartment rear wall deep drawn to provide a channel in which moist air within said compartment can travel to said upper evaporator.

7. In a refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining a food storage compartment, an insulating breaker strip connecting together the edges of said casings and defining an opening for said compartment, a door for closing said opening, a foraminous insulating top wall for said compartment, said strip being of substantially U-shaped configuration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top wall of said storage compartment a recess, a compressor, a condenser without said cabinet, a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment top wall in serpentine configuration and sloped rearwardly, said upper evaporator having one side extending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said upper evaporator arranged to be operated at a lower temperature than said remaining evaporators to cause frost to migrate to said upper evaporator only, means to defrost said upper evaporator and plate after a predetermined period of compressor operation, a liquid reservoir supported by and in heat transfer relationship with said condenser, means extending through said casings to conduct defrost water from said upper evaporator and plate to said liquid reservoir whereby said water is evaporated to the outside air by said condenser.

8. Ina refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining a food storage compartment, an insulating breaker strip connecting together the edges of said casings and defining an opening for said compartment, a door for closing said opening, a foraminous insulating top wall for said compartment, said strip being of substantially U-shaped configuration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top wall of said storage compartment a recess, a compressor, a condenser without said cabinet, a

plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment adjacent said top wall in serpentine configuration and sloped rearwardly, said upper evaporator having one side extending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said upper evaporator arranged to be operated at a lower temperature than said remaining evaporators to cause frost to migrate to said upper evaporator only, means to heat said upper evaporator and plate, timing means acting after a predetermined period of compressor operation to energize said heating means, said timing means and compressor being de-energized when said heating means are energized, means responsive to the temperature of said upper evaporator and plate to de-energize said heating means and energize said compressor and timing means, and means to drain said defrost Water from said cabinet.

9. In a refrigerating apparatus, a cabinet comprising an inner and outer spaced-apart casing with thermal insulation disposed between said casings, said inner casing defining a food storage compartment, an insulating breaker strip connecting together the edges of said casings defining an opening for said compartment, a door for closing said opening, a foraminous insulating top wall for said compartment, said strip of substantially U-shaped configuration along the top of said opening and having a substantially L-shaped rear end extending upwardly and forming with the top wall of said storage compartment a recess, a compressor, a condenser without said cabinet, a plurality of serially connected, vertically spaced evaporators within said compartment with the upper evaporator extending across said compartment in serpentine configuration, adjacent said top Wall and sloping rearwardly, said upper evaporator having one side extending within the space defined by said recess, a metallic plate arranged below and attached to said upper evaporator, said upper evaporator arranged to be operated at a lower temperature than said remaining evaporators to cause frost to migrate to "said upper evaporator only, a fluid conducting trough along said plate rear edge, tubing extending through said casings to conduct water from said trough externally of said cabinet, heating means for said tubing, trough, and plate, timing means for energizing said heating means after a predetermined period of compressor operation, said heating means acting to warm sequentially said tubing, trough, and plate, said timing means and compressor being de-energized when said heating means are energized, and temperature responsive means to deenergize said heating means and energize said compressor when said upper evaporator and plate reach a predetermined temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,370,267 Starr Feb. 27, 1945 2,663,160 Young Dec. 22, 1953

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