US2701450A

US2701450A - Automatic defrosting mechanism

Info

Publication number: US2701450A
Application number: US144641A
Authority: US
Inventors: Duncan Thomas William
Original assignee: Seeger Refrigerator Co
Current assignee: Seeger Refrigerator Co
Priority date: 1950-02-17
Filing date: 1950-02-17
Publication date: 1955-02-08
Anticipated expiration: 1972-02-08

Description

Feb. 8, 1955 T. w. DUNCAN AUTOMATIC DEFROSTING MECHANISM 3 Sheets-Sheet 1 Filed Feb. 17. 1950 Ina:

INVENTOR. WWW gfla 1101: n

Feb. 8, 1955 r. w. DUNCAN 2,701,450

' AUTOMATIC DEFROSTING MECHANISM Filed Feb. 17, 1950 :s Sheets-Sheet 2 "9 'rnmnoam' 97 83 la? f 94 9:

31/ 1M 1 mtg 5mm i LINE 99 conmzssoa j'm f m '82 umr 67 wncu 88 1047 no.|. EVAPORATOR 90 Q conmssson 92 h -26 MOTOR ASSEMBLY swn'cn 9/ CABINET ucmr INVENTOR.

Feb. 8, 1955 T. w. DUNCAN 2,701,450

AUTOMATIC DEFROSTING MECHANISM Filed Feb. 17, 1950 3 Sheets-Sheet 3 IN VEN TOR.

United States Patent 2,701,450 AUTOMATIC DEFROSTING MECHANISM Thomas William Duncan, Evansville, Ind., assignor to Seeger Refrigerator Company, St. Paul, Minn., a corporation of Minnesota Application February 17, 1950, Serial No. 144,641

9 Claims. (Cl. 62-4) .been operated for a predetermined period of time, which depends upon the length of time during which the door has been opened, as the amount of frost collected on the evaporator is determined to a large extent by the amount of warm air which is allowed to enter the cabinet, which is, in turn, governed by'the length of time that the cabinet door is open.

Another object is the'provision of an improved defrosting mechanism which is adapted to totalize the length of time during which the door of a-cabinet of a household refrigerator is open, and upon reaching a predetermined total the mechanism is adapted to accomplish a sequence of events which lead to the defrosting of the evaporator and the resetting of the mechanism for totalizing.

Another object -is the provision of an improved defrosting mechanism which utilizes an-electric heater, and in which the electric heater is most efficiently applied so that the defrosting will be accomplished evenly and completely and there will be no hot spots developed; the

foregoing being accomplished by a maximum refrigerant circulation taking place in the evaporator when the heat is applied.

Another object is the provision of an improved defrosting system in which provision is made for automatic disposal of the water or condensate resulting from the defrosting, by utilizing the heat of the condenser and/ or the motor compressor to evaporate the condensate.

Another object is the provision of an improved defrosting system in which the length of time between defrosting operations is controlled by the amount of time the door of the cabinet is permitted to remain open, and in which the same mechanism is totalizing the open time periods of the door and is utilized for timing thedefrosting operation.

Another object is the provision of an improved defrosting system in which the motor compressor is automatically disconnected or deenergized during the defrosting operation, and in which the automatic mechanism may be overridden at any time by a manual control so that the user on concluding that defrosting should be accomplished at once, can advance the cycle manually, or the user can delay the defrosting or extend the length of period during which defrosting is accomplished, or expedite the return of the mechanism to its normal operation betwen defrosting periods.

Another object is the provision of an improved system of the class described, which is simple in construction, certain and positive in its action and operation, and which may have its characteristics predetermined for more humid or less humid conditions, depending upon the area in which the refrigerator is to be used.

Another object of the invention is the provision of a mechanism which maybe manufactured at a low cost, which has a long life, and which may be operated throughice nection of the heater from the circuit before the timing device stops so that there will be no possibility of heater operation without timing control.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings, of which there are three sheets, accompanying the specification,

Fig. 1 is a vertical sectional view taken through the cabinet of a. household refrigerator, and showing the evaporator and mechanism in elevation;

Fig. 2 is a diagrammatic plan view of the switch operating mechanism and the manual control which permits overriding of the automatic control by the user;

Fig. 3 is a fragmentary sectional view taken on the plane of the line 33 of Figure 2, showing the gears and clutch for permitting manual control;

Fig. 4 is a fragmentary sectional view taken on the plane of the line 4-4 of Figure 2, looking in the direction of .the arrows, showing the cam and switch mechanism;

Fig. 5 is' an end elevational view of the control knob and the indicator plate beneath it, seen from the bottom of Figure 2;

Fig. 6 is a schematic wiring diagram of the defrosting system; and

Fig. 7 is a fragmentary view similar to Figure 1, showing a modified form of liquid disposal system.

Referring to Fig. 1, 10 indicates in its entirety a household refrigerator equipped with a defrosting system embodying my invention. Such a refrigerator comprises a cabinet havingan outer shell 11, an inner liner 12 spaced from the outer shell, and the space between them filled withinsulation 13.

The cabinet may have a food storage compartment 14 containing an evaporator 15 which serves to cool the food storage compartment 14, and also serves to provide a freezing compartment which is closed by means of a cover 16. The cabinet 11 is opened at the front and is closed by means of a door 17, and may be provided at its lower end with a machine compartment 18, which includes a motor compressor 19 and a condenser 20.

The machine compartment 18 has a door 21 at its forward end, and is open at its rear end.

The condenser 20 extends across the currents of air which enter at the opening 22 below the door, and which A pass around the motor compressor 19 and out the open back of the machine compartment 18.

The machine compartment 18 has guides 23, which may support a condensate evaporation pan 24.

In the present embodiment of the invention the system includes an electric heater plate 25 suitably enclosed, and preferably located below the bottom of the U-shaped evaporator 15, where it will produce the maximum circulation of the refrigerant in the evaporator and produce a defrosting action, which is even and complete, without hot spots. The terminals and conductors from the heater are sealed against moisture and vapor to prevent short circuits or grounds.

The heater is preferably of the type in which a resistance wire is enclosed and insulated in refractory covered by a copper tube.

The heater is preferably enclosed in a metal case so constructed that the case will be free to drain any moisture that may have accumulated during the refrigeration cycle. Aluminum wool or turnings may be packed into the case of the heater for facilitating the transfer of heat to the evaporator, with which the heater case is in contact, thereby lowering the operating temperature of the heater.

Below the heater there is a collection system for the condensate, which includes a condensate collecting tray 26, which is preferably slightly larger than the heater and evaporator in bottom plan, so that all moisture from the latter will drop into the tray 26.

tube 28, which is located to discharge into a funnel 29. The funnel 29 communicates with a tube 30, which passes through the wall of the cabinet and has a downwardly extending portion 31 extending down the outside of the shell. The tube 31 is turned inward at 32, and has its lower discharge end portion 33 so located that it discharges into the evaporating tray 26.

Referring to Fig. 7, this is a modification in which the collection system has its downwardly extendingcom duit in the form. of a corrugation or pressed groove'34 formed in the liner 35. This groove is of sufficient size and such contour that the water will be conducted to the bottom of the liner'without spreading over the wall of the liner.

At its lower end the liner slopes toward the discharge port 36 over its entire bottom 37 and over a ledge 38 at the bottom of the groove so that the condensate all runs through the discharge opening 36. This communicates with a conduit 39, which extends downwardly and is turned laterally'to discharge into the condensate evaporation tray 24.

In this case the discharge pipe 40 from the collection tray 26 should extend over into contact with the wall of the liner in the groove 34, where it preferably points downwardly to facilitate the direction of the condensate down the groove. tray 24 is preferably surrounded by a tubular rubber connector, which is grooved to be received in a hole in the lower wall of the shell so that it is stably supported by the shell in such position to support the drain line 39.

Thus the water drained from the condensate collection tray during defrosting will be conducted to the evaporation tray 24, which is disposed close to the condenser 20 in each case. The air passing over the evaporating tray 24 and the heat radiated frfom the condenser 20 causes the condensate to evaporate continuously when the motor compressor is operating; and between these periods it evaporates also, at a slower rate.

The evaporator tray should be conveniently removable for cleaning in the event foodstuffs have been spilled in the compartment in such way as to enter the evaporating tra y The defrosting of the refrigerator is controlled by a defrosting control unit 41 (Fig. 1), which is preferably located between the liner 12 and the shell 13 behind the top breaker strip, with its control knob 42 exposed, but covered by the refrigeratorcover 17.

The mechanism of the defrosting control unit includes a self-starting synchronous clock motor, indicated at 43 (Fig. 6), the drive shaft 44 (Fig. 3) of which is provided with a driving pinion 45. The pinion 45 drives a gear 46 (Fig. 2) which is mounted upon hub 47 in a groove 48 for free rotation with respect to the hub 47.

The hub 47 is fixedly mounted on the driven shaft 49 and fixedly supports a spring double acting clutch 50. The clutch 50 comprises a spring spider with a central hole, receiving a reduced part of the hub 47, which may be spun over inside the aperture of the spider. The four spring arms 51 of the clutch bear on the side of the gear 46 and provide a friction drive, which drives the gear, but permits manual adjustment between the gear 46 and the shaft 4% The gear 46 reacts against the collar 52 fixedly carried by the shaft 49. The shaft 49 carries a cam 53, which is adjustably mounted on the shaft by means of a hub 54 and a set screw 55. The cam 53 has a partially circular part 56 of reduced radius corresponding to the frosting time, and a partially circular portion 57 corresponding to the defrosting period. These two circular parts of the cam are joined by two straight portions 58 and 59, comprising the rise and the drop of the cam.

The circular portions 56 and 57 serve as the dwell parts of the cam, during which the control switches are held in predetermined position. The shaft 49 extends forwardly out of the housing of the defrosting control unit 41 through a dial plate 60, which may be provided with the indicia Defrost Control. It may also have a circular scale with scale divisions, indicating the frosting period and the defrosting period, and also an arrow indicating the direction of rotation.

The knob 42 is preferably provided with a pointer or arrow 61, which indicates the position of the cam with respect to the dial plate 60, and shows whether the refrigerator is frosting or defrosting.

the spring actuated snap switch type.

The drain pipe 39 to the evaporator When the system is operating and it is found that unusual conditions have'made a efrostm cycle necessary, but the knob has not arrived at the de rosting point, the knob can then be turned manually to the index point 62 for defrosting; and the defrosting cycle will automatically start and be automatically controlled to completion because the cam 53 turns with the knob 42 and the shaft 49.

If it is found that a defrosting cycle was incomplete because of an initially heavy frost build-up, the knob can be turned to the index point for defrosting, which is permitted by'means of the double acting clutch and the entire defrosting cycle, or any portion ofthe cycle, can be repeated.

If it is found that the knob indicates a defrosting cycle is about to take place, whereas conditions indicate that defrostin is not yet necessary, knob 42 may be turned backwar delaying the defrosting as much as desired.

The same plate may serve both for the defrosting knob and the thermostat adjustment knob (not shown).

The cam 53 actuates a pair of switches, preferably of Such switches include actuatingbuttons 63 and 64, the switches being mounted in a single housing 65 provided with connectors 66 and 67. Such'snap switches of the toggle type require a predetermined motion of the actuating button before they snap from open to closed position, or vice versa, and also permit further motion after they have been actuated, without affecting the switch.

They may be of the type that includes a pair of springs. one for producing the snap action, and the other for urging the switch into a home position; that is, with both actuating

buttons

63, 64 outward.

The presentsystem preferably utilizes switches which permit a time lag between the two

switches

63 and 64; and the snap switches just described have this characteristic, of which I prefer to take advantage, for reasons further to be described.

The cam 53 may act upon a follower 68 (Fig. 4) which is fixedly secured upon a pin 69 by means of a circular portion 70. The follower 68 has its end curved outwardly from the cam at 71 so that it will ride upon the cam freely in either direction. The pin 69 is mounted upon bearings (not shown), and also carries a switch actuating arm 72 fixedly secured to pin 69. The switch actuated arm 72 extends radially, and has a laterally bent end portion 73 forming an actuating flange.

This actuating flange engages separate leaf sprin s 74. 75 for the two

switches

63, 64. The

leaf springs

4, 75 are fixedly secured to the switch unit 65 at their upper end by means of a screw or screw bolt 76. The actual ing flange 72 is cut away at 77 over that portion of it end WhlCh engages the leaf spring 75, but it projccv. farther toward the leaf spring 74.

This means that the actuating flange 72 will come into engagement with the leaf spring 74' first, and will actuate switch 63 first; and upon being moved farther, during' the rise 58 of the cam, the actuating flange 72 will have its edge 77 brought into engagement with the leaf spring 75; and will then actuate the switch 64.

T1118 means that. upon clockwise rotation of the cam 53 switch 63 will be actuated first; and after a slight time lag switch will be actuated next. Upon the discharge of the follower 68 down the sloping surface 59 of the cam 53, a reverse action will take place; and switch 64 will be permitted to move to its former position first; and after a predetermined time lag'switch 63 will move back to its initial osition.

The reason for t is time lag will be further explained after the description of the operating circuit. The operating circuit is shown diagrammatically in Fig. 6, in which the synchronous clock motor has already been indicated by the number 43. The control switches arc shown in the approximate position which. they assume durin the defrosting; and the movable switch arms have been indicated by the

numbers

63 and 64.

The present system is intended to be energized by a 110 volt, 60 cycle source of lighting current. The

switch arms

63, 64 are seen below the double throw switches; and the fixed contacts of these switches have been indicated by'numbers 78-81. The terminals of the clock motor 43 are connected to the moving

switch arms

63, 64; but the moving switch arm 64 is also connected by a conductor 82 to the line conductor 83. The other line conductor 84 is connected by a conductor 85 to the moving contact arm 86 of a synchronous clock motor 43 is energized only when the I door switch is closed; and that 1s, when the door s opened and the light 91 is illuminated.

The purpose of this is to control the operation of the clock motor responsive to the opening of the door. In this manner the running of the clock motor 43 totalrzes the time during which the door is open.

A desirable total'in terms of frost build-up can be determined experimentally, taking into consideration the most severe humidity conditions to be encountered in the field. Thus, when the switch 63 is inns left hand position, the clock motor is adapted to totalize the time during which the door is open and to express this total by means of reducing gears in the rotative movement of the cam 53.

The amount of the periphery which is devoted to the circular part 56 indicates the time which. has been determined experimentally for a build-up of frost on the evaporator; and when the cam has rotated an amount equivalent to the peripheral portion 56, the evaporator will ordinarily have arrived at a condition when defrosting is desirable.

The other position 79 for the switch 63 connects the clock motor directly to the line throu h the

conductors

88 and 85 so that the clock motor is. ta en from the control of the door switch; and the clock motor may now be used for timing the on period of an evaporator heater 25 in the form of an electric heating element, previously described. a

The compressor motor of the motor compressor unit 19 is preferably of the induction type, which does not interfere with radio receiving circuits; and its three energizing conductors 94-96 extend to a motor starting relay 97, one terminal of which 1s connected byconductor 98 to the line conductor 84.

The other terminal of the motor starting relay is connected by the conductor 99 to the fixed contact 100 of a thermostatic switch unit 101. The movable contact 102 of the thermostatic switch unit is connected by conductor 103 to the fixed contact 80 of switch 84, which s the left contact. The fixed contact 81 of switch 64 is connected by conductor 104 to one term nal of the electric heating element 25. The other terminal of the electric heating element 25 is connected by conductor 105 to line conductor 84.

This means that when the switch 64 IS in the left hand position, engaging contact 80, the motor compressor unit is energized under control of the thermostatic switch 101 so that refrigeration may proceed in the normal manner. When the switch 64 is in the right hand position, engaging contact 81, the motor compressor unit is de-energized, even though the thermostatic switch may close, because it is not desirable to operate the motor compressor at the same time as the evaporator heater.

In this, the right hand position of the switch 64, engaging contact 81, evaporator heater 25 1s energized through

conductors

82, 104, and 105. Thus the left hand position of both switches corresponds to the normal operation of the refrigerator and the frosting period,

. during which the clock motor totalizes the amount of door opening; and the movement of the cam depends upon the amount of time the door remains open.

The right hand position of both switches corresponds to the defrosting cycle, during which the clock motor is not controlled by the door switch, but continues to operate and to move the cam through that portion of the cycle corresponding to the evaporator defrosting.

The two

switches

63 and 64 are preferably operated with such a time lag that switch 63 is moved tothe right first, and switch 64 is moved to the right second, after a time lag, as previously described.

Switch 64 is the first to move to the left 111 Flg. 6; and after a time lag, switch 63 moves to the left for safety and to make sure that there is no possibility of the clock motor stopping and remaining still while the heater operates.

This tune lag need only consist of a few seconds, such as, for. example, fifteen to thirty seconds; and tive assurance that the clock will not be stopped by the opening of the door switch after the heater element has been turned on. For example, suppose the last door opening prior to a defrosting period is still going on at the time when the cam arrives at the defrosting period. If the switches were actuated simultaneously, the cam might then turn on the evaporator heater'before the actuation of the switch 63 to disconnect the clock from the control of the door switch.

Manufacturing inaccuracies might permit this to happen, leaving the heater operating and the clock motor under the control of the door switch for a very short time. .Under these conditions, when the door is closed, the door switch would open, stopping the clock motor and also stopping the rotation of the cam. The heater would be operating; but the clock motor would not be timing the heating period.

If the mechanism should ever arrive at this position. the operation of the clock motor would be stopped; and the cam would not act further to close the contacts 63 and 79. The heater would then remain on until the next cabinet door opening; andv if there were no time lag between the switches, at that time, upon opening of the door the clock motor would be energized through contacts 63, 78, and another timed defrosting would probably take place, in addition to the time during which the door was closed and the heater operated without being timed.

There should be no possibility of the heater operating without being timed because of the damage which might occur'from too much heat; and therefore the switches preferably operate with a definite time lag between them so that by having the switch 63 operate before the heater is turned on, the timing motor is always running and ready to control the heater first; and by having the heater cut off first, by means of the switch 64, while the timer is still operating, positive control of the heater and timing of its operations is always assured.

The operation of the automatic defrosting system is as follows: Ordinarily both the

switches

63 and 64 will be in their left hand position, during the normal operation of the refrigerator; and the evaporator heater will be turned off, and the timing motor will be under the control of the door switch.

The motor compressor unit operates in the usual way, being controlled by the thermostatic switch, to compress refrigerant and supply refrigerant to the evaporator only when the temperature rises above a predetermined limit the following reason. It is very desirable for the timing device to be running before the heater is turned on and desirable for the heater to be turned 0E before the timing device is stopped, both from the point of view of at the point where the thermostat is located, whether it be inside the evaporator 15 or on the outside, or in the storage chamber 14.

While the door of the refrigerator is closed, the evaporator 15, being operated at a point below freezing, it i will cause the vapor in the air to condense upon its surface in the form of frost, tending to dehydrate the air in the refrigerator, during the cooling operation. Whenever the door is opened new air gains access to the compartment 14 and to the evaporator 15; and this air contains an amount of moisture, depending upon the humidity conditions at the point where the domestic refrigerator is being used. The amount of frost accumulated depends .upon the length of time the door remains open.

As the clock motor is a self-starting synchronous motor, it will run during the periods of time that the door is open, and will totalize the time during which the door is open by rotating the cam 53 through the reduction gears over a predetermined amount.

When the cam 53 has been rotated to the point where the riser 58 engages the follower 68, switch 63 will be moved to the right, first closing the circuit to the clock motor directly to line, and taking the clock motor out of control of the door switch. The clock motor then continues to operate; and a few seconds later the cam 53, having been rotated further, the riser 58, actuating the follower 68, moves the flange 72 to such a point that the edge 77 engages the switch 64 and moves it toward theright hand position of Fig. 6.

The breaking of the circuit at 64, 80 takes the motor compressor unit completely out of circuit and connects the evaporator heater in circuit. Refrigeration then it is posiceases; and the heating of the evaporator to defrost the evaporator commences.

The electric heater attached to the evaporator raises the temperature of the parts of the evaporator and the refrigerant inside it. The refrigerant rises in the conduits and tends to warm up the entire evaporator. 'The location of the heater or heaters should be selected to give a maximum circulation of the refrigerant. The

heater is kept on during the periodwhen the circular part 57 of the cam passes over the follower 68.

The length of this part of the cam IS experimentally determined for the locality in which the refrigerator IS to be used, and is sufficient to permit the complete deare still operating, but refrigeration commences and the timing of the heating period continues for a short time during the time lag between the switches.

As the follower 68 passes down the inclined portion 59 of the cam to the curved portion 56 of lesser radius, the follower is permitted to move in such manner that the actuator 72 recedes from the switch button 63; and the switch 63 moves from the right hand position to the left hand position in Fig. 6. This cuts the timing motor off the line at the contact 79 and puts it under the control of the door switch 86 again.

Of course, if the door happens to be open at that moment, the timing motor would continue to operate and to rotate the cam until the door is closed.

Thereafter the frosting period takes place again;'and the clock motor totalizes the periods of time during which the door is open and during which frost is being accumulated again.

In the event that the user of the refrigerator wishes to advance the cycle to have the defrosting take place at once, he need only turn the knob 42 in the clockwise direction around to the defrosting indicator 62; and defrosting will take place at once because this will move the cam to the proper position to actuate the switches.

In the event the user does not wish to defrost yet, he may turn the knob 52 backward and may let the refrigerator accumulate frost again for as long a period as he may desire.

If the defrosting has not been complete, the user may again turn the control knob to the defrosting position, all of this being permitted by the clutch 50, which slips with respect to the gear 46.

The condensate which is melted from the evaporator is collected by the pan 26 and conducted by the conduit 31 to the evaporation pan 24 adjacent the condenser in the machine compartment 18.

As the condenser becomes heated and the motor compressor generates heat, the air passing over the evaporation pan 24 will carry away the condensate in the form of vapor; and thus the present system isadapted to dispose of the condensate resulting from the defrosting.

It will thus be observed that I have invented an automatic defrosting mechanism which includes an electric heater for accomplishing the defrosting, a control unit for initiating and controlling'the defrosting cycle, dependent upon the length of time the door remains open, a system of collecting the condensate resulting from defrosting, and a disposal system to eliminate the water which is so collected.

The present system is flexible and may be overridden by manual controls so that it is capable of receiving and responding to such attention as the user desires to give it; but if not given attention, will nevertheless operate automatically.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a refrigeration apparatus having an insulated cabinet having a dooropening, a door for closing'the opening, an evaporator, a condenser and a motor compressor, the evaporator being operably connected with to operate said timer for the duration of time the door is open and means actuated by said timer after a predetermined time that the door is open for initiating defrosting of the evaporator by the source of heat.

2. In an automatic defrosting mechanism, the combination of an insulated cabinet having a door opening and a door, an evaporator in said cabinet for cooling the space therein, a motor compressor'and condenser connected with said evaporator, an electric heater in heat transmitting contact with a part of said evaporator, a door switch adapted to be closed when the door is opened, and a timing mechanism comprising a syn chronous timing motor, a shaft driven by said motor and a cam carried by said shaft, a driving clutch connection between the said shaft and said timing motor, an indicating knob carried by said shaft and having indicia for indicating the beginning and end of a defrosting period and the beginning and end of cooling operations, said shaft being rotatable relative to said timing motor by said indicating knob for the purpose of advancing or retarding or predetermining the time of defrosting or cooling operations, said timing motor being controlled by said door switch and energized during cooling operation by the opening of the door to totalize the time of door opening, during which the evaporator is subjected to increased frosting from the moisture in the air entering through the door opening, the said cam having a dwell of one radius of predetermined peripheral length corresponding to the total time of door opening during which frost may be permitted to accumulate, and the said cam having a dwell of another radius having a peripheral length corresponding to the length of time during which it is desired to operate the electric heater for heating the refrigerant in the evaporatorand thereby melting the frost from the evaporator, switching means controlled by said cam for opening the motor compressor circuit and for closing the heater circuit at the beginning of a defrosting period, said switching means also disconnecting the timer motor from the door switch and placing the control of the timer motor in parallel with the heating element, the said switching means also reestablishing the motor compressor circuit and the door switch control-of the timer motor and interrupting the heater circuit at the end of a defrosting period, the-switching means being provided with a time lag action between the making of the parallel circuit for the timer motor and the breaking of the door switch circuit so that the timer motor will be in condition to operate at all times to advance the cam through its respective periods of cooling operations and defrosting operation without possibility of stoppage of the timing motor by switching operations.

3. In a refrigerator, the combination of a cabinet with a door. an evaporator, a motor compressor, and a condenser, a door switch having contacts which are closed when the door is open. a synchronous clock motor controlled by said door switch and operated to run when the door is open. a mechanical device operated by said clock motor and arranged to operate a first electric switch when the door has been open over a predetermined amount of time, said first switch disconnecting the clock motor from the control of the'door switch and connecting the clock motor to line, a second switch actuated by said device, and an electric heater in proximity to the evaporator. said second switch connecting the electric heater with the line and disconnecting the motor compressor from energization so that the refrigerator will not operate while the heater is defrosting the evaporator.

4. In a refrigerator, the combination of a cabinet with a door, an evaporator, a motor compressor, and a condenser, a door switch having contacts which are closed when the door is open, a synchronous clock motor controlled by said door switch and operated to run when the door is open, a mechanical device operated by said clock motor and arranged to operate a first electric switch when the door has been open over a predetermined amount of time, said first switch disconnecting the clock motor from the control of the door switch and connecting the clock motor to line, a second switch actuated by said device, and an electric heater in proximity to the evaporator, said second switch connecting the electric heater with the line and disconnecting the motor compressor from energization so that the refrigerator will not operate while the heater is defrosting the evaporator, said mechanism including an actuator for said first and second switches, which operates the switches with a time lag between them to assure the constant connection of the synchronous clock motor in circuit so that the operation of the heater will be timed whenever it is connected in circuit.

5. In a refrigerator, the combination of a cabinet with a door, an evaporator, a motor compressor, and a condenser, a door switch having contacts which are closed when the door is open, a synchronous clock motor controlled by said door switch and operated to run when the door is open, a mechanical device operated by said clock motor and arranged to operate a first electric switch when the door has been open over a predetermined amount of time, said first switch disconnecting the clock motor from the control of the door switch and connecting the clock motor to line, a second switch actuated by said device, and an electric heater in proximity to the evaporator, said second switch connecting the electric heater with the line and disconnecting the motor compressor from energization so that the refrigerator will not operate while the heater is defrosting the evaporator, said device comprising a cam and a follower, and said cam having two dwell portions of different radius, one of which corresponds to the frosting period, and the other of which corresponds to the defrosting period.

6. In a refrigerator, the combination of a cabinet with a door, an evaporator, a motor compressor, and a condenser, a door switch having contacts which are closed when the door is open, a synchronous clock motor controlled by said door switch and operated to run when the door is open, a mechanical device operated by said clock motor and arranged to operate a first electric switch when the door has been open over a predetermined amount of time, said first switch disconnecting the clock motor from the control of the door switch and connecting the clock motor to line, a second switch actuated by said device, and an electric heater in proximity to the evaporator, said .second switch connecting the electric heater with the lin and disconnecting the motor compressor from energiz.ztion so that the refrigerator will not operate while the heater is defrosting the evaporator, and a friction clutch interposed between said devices and said clock motor, and having a manual actuating member so that the frosti or defrosting may be advanced or retarded by using saiJ clutch to control frosting or defrosting at will.

7. Refrigerating apparatus of the type having a heatabsorbing unit connected in a closed circuit with a heat-dissipating unit and in which the heat-absorbing u is disposed within an insulated space from which heat is to be removed, said apparatus comprising a mechanism for controlling operation of said apparatus in accordance with the temperature of said space, a heat source for causing the temperature of said heat-absorbing unit to raised to a degree sufiicient to melt any frost which may have collected thereon, a movable door for providing access to said insulated space, timing means operable in response to the total elapsed time during which said door has been opened for initiating operation of said heat source and for restoring the system to the control of the normal operation control mechanism.

8. An automatic defroster system for refrigerator evaporators, comprising a source of electric current, a refrigerator door switch arranged to be closed by open ing the door and opened when the door is closed, an electric timer motor, conductors connecting said source, motor and door switch, the timer motor operating when the door is open to integrate the total door-open time, an electric heater for heating refrigerant in the evaporator to defrost the latter, a reduction gear and cam driven through said gear by said timer motor, a heater switch controlled by said cam, to be closed after the timer motor has run a predetermined time, and conductors connecting said source, heater and heater switch, to energize said heater to initiate defrost after the door has been open a predetermined total time, which results in the frosting of the evaporator sufficiently to require defrost.

9. In an automatic defrosting refrigerator,'the combination of an insulated cabinet, having a door opening and a food storage space, an insulated door movably mounted on said cabinet, to open or close said door opening, a door seal maintaining an air-tight joint between said door and cabinet, a door switch arranged to be closed by opening the door and opened when the door is closed, a timing motor connected to be controlled by said door switch to operate when the door is open, to integrate the times when the door is open and the food storage space of the cabinet is open to damp external air, an evaporator in the cabinet operated at a temperature below freezing point of water to cool the air and contents of the cabinet, the said evaporator gathering an amount of frost from moisture in the air, dependent on the total time the door is open, a motor compressor and a condenser outside the food storage space, connected by conduits in closed circuits with said evaporator, a thermal switch controlling said motor compressor, responsive to evaporator temperature, to supply the evaporator with cooling refrigerant, when the evaporator temperature rises above a predetermined degree, an electric heater for heating refrigerant in the evaporator and to cause the hot refrigerant to be circulated in said evaporator, to melt the frost from said evaporator, and electric switch means controlling said heater and closed by said timing motor, after said door open periods have amounted to a predetermined total time, to initiate the defrost of said evaporator.

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