US2736173A - duncan - Google Patents

Description

Feb. 28, 1956 T. w. DUNCAN 2,736,173

AUTOMATIC REFRIGERATOR DEFROSTERS Filed Feb. 21, 1952 2 Sheets-Sheet l INVENTOR. 7 #017705 W 00/7001,

Feb. 28, 1956 T. w. DUNCAN 2,736,173

AUTOMATIC REFRIGERATOR DEFROSTERS Filed Feb. 21, 1952 2 Sheets-Sheet 2 J 5 47 4g T/ZI'WOfWiZC/d 01 7 -55 Heazer 0/ fvapor or AA v 46 aiiorrzgy United States Patent 2,736,173 AUTOMATIC REFRIGERATOR DEFROSTERS Thomas W. Duncan, Evansville, Ind., assignor, by mesne assignments, to Whirlpool-Seeger Corporation, a corporation of Delaware The present invention relates to automatic defrosters, and is particularly concerned with defrosters of the type utilizing an electric heater in which the defrost cycle is initiated automatically responsive to a timer switch which integrates the amount of time during which the refrigerator door is open.

One of the objects of the invention is the provision of an improved defrosting system which is adapted to accomplish the function of defrosting after the refrigerator has been operated for a predetermined period 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 totalizmg.

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 the defrosting 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 between 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 may be manufactured at a low cost, which has a long life, and which may be operated throughout the life of the household refrigerator without necessity for repair or replacement of its parts.

Another object is the provision of an improved defrosting system of the class described in which the defrost cycle is initiated by an electric timer, which is automatically disconnected from the circuit when the defrost cycle is initiated and in which the defrost cycle is termihated pursuant to temperature control of the evaporator, so that the system will not be thrown out of order or affected by a user opening the door and holding it open for the purpose of observing the defrosting cycle.

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 two sheets, accompanying the specification,

Fig. l is a diagrammatic elevational view of the defroster control, with the parts in the position which they assume when the cabinet is being refrigerated subject to the control of the usual thermostatic switch which controls the compressor;

Fig. 2 is a similar view, showing the parts in the position which they assume when the refrigeration system has been operating and the times of door opening have been integrated until a defrosting cycle is about to be initiated;

Fig. 3 shows a similar view with the parts in the position which they assume when defrosting is taking place;

Fig. 4 is a diagrammatic view in perspective of the timing mechanism, showing the structure which permits the operator to advance the timing cam at will to initiate defrost or to terminate defrost if desired;

Fig. 5 is a wiring diagram for the present refrigeration system;

Fig. 6 is a vertical front-to-back cross-sectional view of a cabinet embodying the invention;

Fig. 7 is a view in perspective of one type of evaporator which may be employed in the system;

Fig. 8 is an enlarged, fragmentary sectional view taken on the plane of the line 88 of Fig. 1, looking in the direction of the arrows, showing the contact springs and the insulating spacer which controls their operation.

Referring to Fig. 6, 10 indicates one type of refrigerator cabinet having an outer shell 11 and an inner liner 12 separated from each other by insulation 13, and provided with breaker strips 14 joining the liner and shell about a door opening.

The cabinet is provided with an insulated door 15, having a suitable rubber seal 16 for effecting an air tight closure and a door switch 17 is moved to closed position whenever the door is opened for controlling an electric bulb 18 which illuminates the cabinet.

The refrigeration system includes the usual condenser 19, a motor compressor 20, a capillary tube restrictor (not shown) and an evaporator 21. The evaporator may be varied in construction but preferably has its conduits so arranged that the heating of the lowermost tubes causes the refrigerant to boil up toward a header or receiver, so that all of the evaporator may be quickly heated by the hot refrigerant.

Thus the present evaporator comprises a U-shaped metal member having the vertical sides 22, 23, joined by the flat bottom 24, and provided with an ice tray shelf ,end and the other end communicates with sinuous tubes at 29 and 30. The refrigerant inlet from the capillary tube is connected by means of a tube 31, which is connected to the sinuous tubes 32, carried by the lower side of the shelf and extending back and forth and substantially covering the bottom of the shelf.

At 33 the sinuous shelf tubes extending through the side wall 22 are arranged sinuously back and forth across the side wall 22 on the outside thereof, and back and forth across the bottom wall 24 on the bottom thereof, and back and forth across the side wall 23 on the outside thereof until the tubing reaches the inlet to the receiver 27.

The tubing 34 on side wall 22 and 36 and on side wall 23 preferably has a slope with respect to the horizontal so that the tubing has a constantly downward pitch, L.

aiding in the passage of liquid downward and gas upward.

All the tubing is ntegrally welded to the shelf and side walls, and the tubing 34 leads to a depending U-shaped leg 37a carrying electric heater 37 of the type having an electric heater imbedded therein, which is surrounded by heat resistive and heat insulating powder, insulating it from an outer copper tube. The heater 37 may have a clamp to engage refrigerant tube 37a for the best heat transmission.

The evaporator is carried by suitable brackets 38 from the top of the liner and brackets 39 from the rear wall, and is provided with a hinged cover 46, closing the front of the evaporator, and with a drip pan 41, draining to an outlet 42 above a funnel 43.

Funnel 43 communicates by means of pipe 44 with the evaporation pan 45, carried by the bottom 46 of the cabinet below the condenser 19. Thus any condensate which is melted and carried to the condensate pan may be evaporated by the heat from the condenser and the compressor and carried away by the air passing over it.

All of the details of the evaporator may be substantially as disclosed in the copending application of myself and Albert C. Rosencranz, Ser. No. 242,462, filed August 18, 1951, now Patent No. 2,654,226, issued October 6, 1953.

Referring to Fig. 5, this is a wiring diagram in which 47 and 48 are the line conductors for the usual 110 volt, 60 cycle lighting circuit current.

The door switch 17 is connected in series by means of conductors 49 and 50 with the bulb 18 for illuminating the cabinet. The door switch 17 is connected by conductor 51 in series with a resilient timer contact 52 and an electric timer motor 53.

The timer motor may consist of any synchronous elec tric timer which operates responsive to the cycle current. The resilient timer contact spring 52 may carry a special beryllium contact 54, projecting above and below the spring and riveted in an aperture in the spring.

The defrosting is controlled by a thermoswitch unit 55, which includes the timer contact spring 52, a heater contact spring 56, a common contact spring 57 and a refrigeration contact spring 58.

The common contact spring again has a beryllium spring 59, projecting from both sides, while the heater contact spring 56 has a beryllium contact 66, and the refrigeration contact spring 58 has a beryllium contact 61, the latter two only projecting from the inner side of the springs.

All the beryllium contacts are in alignment and the common contact spring 57 projects beyond the contact springs 56 and 52, as shown in Fig. 1, for engagement with a latching member 62. The refrigeration contact spring ,58 projects beyond the common contact spring sufliciently to engage a defrosting cam 63, Fig. 1.

* The four contact springs may be supported by a common insulating base 64 in spaced relation to each other and are provided with legends, H for the contact spring 56, indicating a heater; C for contact spring 57, indicating a common contact; T for contact spring 52, indicating the timer; and R for contact spring 58, indicating refrigeration.

Referring again to Fig. 1, the heater contact spring 56 has its terminal connected to an electrical resistance heater 37, the other terminal of which is connected to line 48. The common contact spring 57 is connected by conductor 65 to line conductor 47.

The timer contact spring 52 is connected by conductor 66 to the timer terminal, which in turn is in series with the door switch 17. The refrigeration contact spring 58 has its terminal connected by conductor 67 to a thermostatic switch 68, actuated by a bellows and bulb which is disposed close to the refrigeration shelf 25.

The other terminal of the thermostatic switch 68 is connected by conductor 69 to the motor compressor controlling relay, and motor compressor indicated at 20. The other terminal of the motor compressor relay is connected by conductor 70 to the line 48.

It should be understood that the motor compressor usually has an induction motor which requires a starting relay for its control (not shown).

Referring to Fig. 8, the contact springs 56 and 58 are wide enough so that they can be provided with apertures 71 and 72 for receiving the upwardly and downwardly projecting lugs 73 and 74 of an insulating spacer member 75.

The spacer member 75 is substantially rectangular in shape and comprises a frame having a rectangular aperture 76, and a second rectangular aperture 77, separated by an insulating bridge 73. The end of the frame 75 is located below the heater contact spling 56, which is biased downward.

The lower end of the frame 75 is located above the refrigeration contact spring 58, which is also biased downward but is so located that it constantly retains the lug 74 in the aperture 72.

The common contact spring 57 is biased downward to the position of Fig. l, but can be lifted to the position of Pig. 2 by the spacer 75, and can be held in that position by the latch 62. The timer spring contact 52 is spring loaded in a direction away from the cam 63, but is restrained from engaging the common contact 57 by the bridge 73 of the spacer when the parts are in the position of Fig. 3.

The latch 62 is pivotally mounted at 79 and is urged by a spring 80 toward the latching position of Fig. 2 from the unlatched position of Fig. l. A beveled surface 81 permits spring 57 to push the latch back as the spring 57 rises from the position of Fig. l to that of Fig. 2. Then the spring 57 is retained by the shoulder 81a.

Latch 62 may carry an adjustable screw bolt 82 which engages the moving end 83 of a bellows 84, having its fixed end 85 communicating through a capillary tube 86 with a bulb 87. Bulb 87 contains a volatile refrigerant which vaporizes when the evaporator reaches a predetermined temperature, which is so selected that the entire evaporator will be defrosted when that temperature is reached.

Bulb 87 may be located close to the shelf 25 and the receiver 27, toward which the heated refrigerant moves by boiling, or the bulb may be located close to the heater 37 on the evaporator, in which case the bellows 84 would be so adjusted as to be actuated at a higher temperature so as to prevent injury to the evaporator.

The timer mechanism 53 may drive a shaft 88, having a pinion 89 driving a gear 96. Gear 90 may rotate a shaft 91, the teeth of which serve as a ratchet wheel as well as a pinion by means of a pawl 92. Pawl 92 is pivotally mounted at 93 on gear 90, and has a spring 94 urging its pointed end into engagement with the ratchet shaft 91.

Gear 90 rotates freely with respect to shaft 91, except when the gear 9-!) is rotated in the direction of the arrows, when it drives the shaft 91 through the pawl 92. Shaft 91 may, however, be rotated counterclockwise, in Fig. 4, the pawl 92 ratcheting over the teeth.

Shaft 91, acting as a pinion, drives the gear 95, carried by shaft 96, which also carries cam 63 and manual adjustment knob 64. The adjustment knob 64 may be provided with an arrow 97, pointing toward fixed arrow 98, when the cam 63 is arranged at the defrosting position of Fig. 4.

Cam 63 may comprise a plate having a central bore 99, by means of which it is fixedly mounted on shaft 96. The periphery 180 of cam 63 is formed on an increasing radius which starts at a minimum length at 101 and remains at that value until about the point 102, when the periphery of the cam has a rise formed on a longer radius at 103, and provided with a drop at 104.

The cam may rotate once each twelve minutes, thus instituting a defrosting cycle whenever the total amount of door opening has risen to the amount of twelve minutes time.

The operation of the present defrosting system is as follows:

The position of Fig. 1 indicates the position of the four switch blades during one phase of the cycle, when the thermostat 84 has just released the latch 62 by expanding and rotating the latch counterclockwise.

At this time the common contact spring 57 is out of engagement with the heater but is engaging the timer switch contact, and this in turn engages the refrigeration contact 5'8. The defroster control position of Fig. 1 thus energizes both the timer and the refrigerator cornpressor by connecting the timer to the line 47, their other terminals being connected to the line 48.

Whenever the door is opened the door switch 17 not only energizes the light 18 for illumination but it also energizes the timer. The timer runs while the door is open and while warm air has access to the evaporator, this warm air being the major cause of frosting. When the door again closes the timer stops but the timer integrates the periods during which the door is open; and when twelve minutes of total door opening have elapsed the timer cam will have been rotated from the position of Fig. l to that of Fig. 2, approaching a defrosting cycle.

The rise 193 of the cam has then lifted the refrigeration contact spring from the position of Fig. 1 to that of Fig. 2, lifting the timer and common contacts with it until the common contact has moved up above the latching shoulder 81a and has become latched by the latch 62.

The heater contact is still open in Fig. 2 and the timer and refrigeration contacts are still closed. The spacer 75 has moved the heater contact upward also, keeping it open. When the contact spring 58 passes over the drop of the cam 63, the parts move to the position of Fig. 3, and the spring bias of the refrigeration contact spring 5?- moves it downward to the lowest radius of the cam, permitting the heater contact 56 to follow it under its own bias engaging the common contact 57.

The common contact is latched in this position, but the timer contact is broken and spaced both from the common contact and the refrigeration contact. The motor compressor unit cannot operate during the defrosting cycle and the timer cannot operate during the defrost cycle, but the heater 37 is energized; and it transmits heat to the refrigerant contained in leg 37a, causing the refrigerant to boil up both sides of the evaporator and across the shelf to the receiver 27.

The entire evaporator is thus heated beginning from the bottom; and the last part to be heated is that portion adjacent the receiver 27, which is also heated by the boiling refrigerant. The thermostat 84 is so set that when it attains a temperature at which all of the frost has been melted off, the bellows 84 expands and moves the latch 62 clockwise, unlatching the contact 57 so that it moves from the position of Fig. 3 to that of Fig. 1.

This breaks the heater contact and causes the timer and refrigeration contacts to become engaged with the common contact, placing the timer under the control of the door opening and placing the motor compressor under the control of the usual thermostat switch 68.

The latter causes the motor compressor to operate whenever there is a demand for refrigeration as indicated by evaporator temperature, as the bulb of the thermostat is preferably disposed on the side of the evaporator adjacent the shelf.

The manual control 64 for the defroster can be advanced by the user at any time by turning it clockwise, which will cause the shaft 91 to rotate counterclockwise, ratcheting under the pawl 92, This permits the cam 63 to be rotated clockwise without moving the timer clock 53. Thus the user can advance the cam to the defrosting position at any time, if it is concluded that defrosting is needed.

It will thus be observed that I have invented an improved defroster control in which the defrost may be initiated manually if desired, but is normally controlled by the amount of door opening periods which are integrated by a timer motor.

The timer cannot operate while the defrosting is going on, and it will not affect the system if the user should open the door at that time and observe the defrosting going on. Defrosting continues until the evaporator reaches predetermined temperature at which all frost is melted off. The melted condensate is collected by a drip pan and runs down a conduit to an evaporating pan adjacent the condenser and compressor, where the condensate will be evaporated so that no attention need be given the refrigerator insofar as defrosting is concerned.

virus i have illustrated a preferred embodiment of try 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:

l. A refrigeration apparatus having a motor compressor in combination with a defroster control unit, an electric heater for defrosting said apparatus, an insulating support, a plurality of contacts movably mounted on said support, a heater contact for controlling said electric heater, a refrigeration contact for controlling said motor compressor, and a common contact for connection to either one of the heater or refrigeration contacts, an electric timer motor, and a cam operated by said timer motor and having a rise and fall for controlling the movement of one of said contacts, insulating spacing means acting between said one contact and the other two contacts and causing the movement of all three contacts when said one contact is moved by the rise of said cam from a first to a second position, means for holding said common contact in said second position when the fall of said cam reaches said one contact, said one contact and spacer then receding to said first position, and said heater contact moving into engagement with said common contact to establish a heating cycle, and thermostatic means for controlling the release of said holding means, and terminating the heating cycle at a predetermined temperature, the common contact then closing with the refrigeration contact after separating from the heater contact.

2. A defrosting refrigeration system, comprising a refrigerator cabinet, an evaporator in said cabinet, a motor compressor, a condenser, said cabinet having a door, and a door switch controlled by the opening or closing of said floor, said door switch being closed when the door is opened, a timing motor controlled by said door switch and driving a cam responsive to the amount of time the door is open, during which the evaporator is exposed to damp exterior air, said cam having a rise and a drop and actuating a resilient switch arm carrying a refrigeration contact, a common insulating support, a timer resilient switch arm, a common energized resilient switch arm, and a heater resilient switch arm carried by said support, the said cam and switch arms operating with a common, timer, and refrigeration contacts engaged until the cam rise reaches a predetermined point, when the actuation of the refrigeration contact causes the opening of the re frigeration and timer contacts, and the closure of the heating contact cutting off refrigeration and energizing an electric heater for defrosting said evaporator, and a latching means for engaging the common contact and holding it in engagement with the heater contact after said cam passes its rise and drop.

3. A defrosting refrigeration system, comprising a refrigerator cabinet, an evaporator in said cabinet, a motor compressor, a condenser, said cabinet having a door, and a door switch controlled by the opening or closing of said door, said door switch being closed when the door is opened, a timing motor controlled by said door switch and driving a cam responsive to the amount of time the door is open, during which the evaporator is exposed to damp exterior air, said cam having a rise and a drop and actuating a resilient switch arm carrying a refrigeration contact, a common insulating support, a timer resilient switch arm, a common energized resilient switch arm, and a heater resilient switch arm carried by said support, and insulating spacer means operated by said refrigeration contact arm for moving said heater switch arm with the refrigeration contact arm to keep the heater contact arm on open circuit until the refrigeration contact arm passes the drop in said cam which opens the timer and refrigeration contacts, the said cam and switch ms operating with a common, timer, and refrigeration contacts engaged until the cam rise reaches a predetermined point, when the actuation of the refrigeration contact causes the opening of the refrigeration and timer contacts, and the closure of the heating contact cutting off refrigeraion and energizing an electric heater for defrosting said evaporator, a latching means for engaging the common contact and holding it in engagement with the heater contact after said cam passes its rise and drop, and thermostatic means operated responsive to evaporator temperature, for unlatching said latching means, resulting in the opening of the heater contact and the closing of the timer and refrigeration contacts into engagement with the common contact.

4. A defrosting refrigeration system, comprising a refrigerator cabinet, an evaporator in said cabinet, a motor compressor, a condenser, said cabinet having a door, and a door switch controlled by the opening or closing of said door, said door switch being closed when the door is opened, a timing motor controlled by said door switch and driving a cam responsive to the amount of time the door is open, during which the evaporator is exposed to damp exterior air, said cam having a rise and a drop and actuating a resilient switch arm carrying a refrigeration contact, a common insulating support, a timer resilient switch arm, a common energized resilient switch arm, and a heater resilient switch arm carried by said support, and insulating spacer means operated by said refrigeration contact arm for moving said heater switch arm with the refrigeration contact arm to keep the heater contact arm on open circuit until the refrigeration contact arm passes the drop in said cam which opens the timer and refrigera tion contacts, the said cam and switch arms operating with a common, timer, and refrigeration contacts engaged until the cam rise reaches a predetermined point, when the actuation of the refrigeration contact causes the opening of the refrigeration and timer contacts,'and the closure of the heating contact cutting off refrigeration and energizing an electric heater for defrosting said evapora- 8 tor, and electric heater carried by the lower part of said evaporator, said evaporator having sinuous conduits extending upwardly from its lower part and communicating at both ends with a receiver, the heated refrigerant boiling up into said receiver to effect defrosting.

5. A defrosting refrigeration system, comprising a refrigerator cabinet, an evaporator in said cabinet, a motor compressor, a condenser, said cabinet having a door, and a door switch controlled by the opening or closing of said door, said door switch being closed when the door is opened, a timing motor controlled by said door switch and driving a cam responsive to the amount of time the door is open, during which the evaporator is exposed to damp exterior air, said cam having a rise and a drop and actuating a resilient switch arm carrying'a refrigeration contact, a common insulating support, a timer resilient switch arm, a common energized resilient switch arm, and a heater resilient switch arm carried by said support, and insulating spacer means operated by said refrigeration contact arm for moving said heater switch arm with the refrigeration contact arm to keep the heater contact arm on open circuit until the refrigeration contact arm passes the drop in said cam which opens the timer and refrigeration contacts, the said cam and switch arms operating with a common, timer, and refrigeration contacts engaged until the cam rise reaches a predetermined point, when the actuation of the refrigeration contact causes the opening of the refrigeration and timer contacts, and the closure of the heating contact cutting off refrigeration and energizing an electric heater for defrosting said evaporator, a manual actuation and indicating knob carried by a shaft supporting said cam, and pawl and ratchet means interposed between said cam and timer motor, permitting the user to advance said cam to defrosting or other position at will, the said pawl riding over said ratchet during said advance, and driving said cam on other occasions.

6. In an automatic defrosting mechanism, the combination of a timing motor with operative gearing connecting said motor to a cam shaft, a switch actuating cam on said shaft, and a switch assembly actuated by said cam, said cam having a rise and a drop, said switch assembly comprising an insulating support, and a resilient heater contact, a resilient common contact, and a resilient refrigeration contact carried by said support, said refrigeration contact being biased toward said cam and engaging said cam, a latching member for holding said common contact in engagement with said heater contact, said common contact being extended for engagement with said latching member, and spacing means of insulation interposed between said refrigeration contact and each of the other two contacts, whereby the rise of the refrigeration contact also actuates the common contact and heater contact, and the common contact is moved to latching position.

7. In an automatic defrosting mechanism, the combination of a timing motor with operative gearing connecting said motor to a cam shaft, a switch actuating cam on said shaft, and a switch assembly actuated by said cam, said cam having a rise and a drop, said switch assembly comprising an insulating support, and a resilient heater contact, a resilient common contact, and a resilient refrigeration contact carried by said support, said refrigeration contact being biased toward said cam and engaging said camfa latching member for holding said common contact in engagement with said heater contact, said common contact being extended for engagement with said latching member, spacing means of insulation interposed between said refrigeration contact and each of the other two contacts, and a resilient timer contact whereby the rise of the refrigeration contact also actuates the common contact and heater contact, and the common contact is moved to latching position, the said heater contact being biased towards the common contact, and upon passing the drop of said cam the refrigeration contact and timer contact move away from the common contact, which is held in engagement with the heater contact by said latching member.

8. In an automatic defrosting mechanism, the combination of a timing motor with operative gearing connecting said motor to a cam shaft, a switch actuating cam on said shaft, and a switch assembly actuated by said cam, said cam having a rise and a drop, said switch assembly comprising an insulating support, and a resilient heater contact, a resilient common contact, and a resilient refrigeration contact carried by said support, said refrigeration contact being biased toward said cam and engaging said cam, a latching member for holding said common contact in engagement with said heater contact, said common contact being extended for engagement with said latching member, and spacing means of insulation interposed between said refrigeration contact and each of the other two contacts, whereby the rise of the refrigeration contact also actuates the common contact and heater contact, and the common contact is moved to latching position, the said heater contact being biased toward the common contact, and upon passing the drop of said cam the refrigeration contact and timer contact move away from the common contact, which is held in engagement with the heater contact by said latching member, and a temperature responsive device to be actuated responsive to the temperature of a defrosted evaporator, for actuating said latching means to release said common contact into engagement with the timer contact and re frigeration contact, breaking contact with said heater contact.

9. In an automatic defrosting mechanism, the combination of a timing motor with operative gearing connecting said motor to a cam shaft, a switch actuating cam on said shaft, and a switch assembly actuated by said cam, said cam having a rise and a drop, said switch assembly comprising an insulating support, and a resilient heater contact, a resilient common contact, and a resilient refrigeration contact carried by said support, said refrigeration contact being biased toward said cam and engaging said cam, a latching member for holding said common contact in engagement with said heater contact, said common contact being extended for engagement with said latching member, and spacing means of insulation interposed between said refrigeration contact and each of the other two contacts, whereby the rise of the refrigeration contact also actuates the common contact and heater contact, and the common contact is moved to latching position, the said heater contact being biased toward the common contact, and upon passing the drop of said cam the refrigeration contact and timer contact move away from the common contact, which is held in engagement with the heater contact by said latching member, and a temperature responsive device to be actuated responsive to the temperature of a defrosted evaporator, for actuating said latching means to release said common contact into engagement with the timer contact and refrigeration contact, breaking contact with said heater contact, said cam shaft having an indicating knob with a defrost indicia on it, and there being a pawl and ratchet interposed in the gearing between the timer and said cam shaft, permitting the user to advance the cam at will to defrosting position, the pawl moving freely over the ratchet.

10. In an automatic defrosting household refrigerator, the combination of an insulated cabinet having an insulated door, an evaporator in said cabinet having freezing coils and food storage cooling coils, a motor compressor, a condenser, and a capillary tube rcstrictor connected in series to said evaporator to form a closed circuit, a thermostatic switch controlling the operation of said motor compressor to maintain said freezing coils at a freezing temperature, an electric heater applied to the lowermost coils of said evaporator, an electric timer motor, a door switch which is closed by the opening of the door, said door switch being connected to said timer to integrate the time periods when the door is open and frost gathers on the evaporator, a cam driven by said timer motor and having a rise for actuating contacts, said cam opening refrigeration contacts connected to said thermostatic switch and compressor and closing heater contacts connected to said heater to initiate a defrost by heating refrigerant which circulates throughout the evaporator coils, when the total time of door openings reaches a predetermined amount, latching means for holding the heater contacts in closed position but biased to open position, and a thermostatic element for acting on said latch and releasing the heater contacts to move to open position responsive to a predetermined increase in evaporator temperature and to restore the closed circuit of the refrigeration contacts.

11. In an automatic defrosting household refrigerator, the combination of an insulated cabinet having an insulated door, an evaporator in said cabinet having freezing coils and food storage cooling coils, a motor compressor, a condenser, and a capillary tube restrictor connected in series to said evaporator to form a closed circuit, a thermostatic switch controlling the operation of said motor compressor to maintain said freezing coils at a freezing temperature, an electric heater applied to the lowermost coils of said evaporator, an electric timer motor, a door switch which is closed by the opening of the door, said door switch being connected to said timer to integrate the time periods when the door is open and frost gathers on the evaporator, a cam driven by said timer motor and having a rise for actuating contacts, said cam opening refrigeration contacts connected to said thermostatic switch and compressor and closing heater contacts connected to said heater to initiate a defrost by heating refrigerant which circulates throughout the evaporator coils, when the total time of door openings reaches a predetermined amount, latching means for holding the heater contacts in closed position but biased to open position, and a thermostatic element for acting on said latch and releasing the heater contacts to move to open position responsive to a predetermined increase in evaporator temperature and to restore the closed circuit of the refrigeration contacts, said timer motor being connected to said cam through reducing gearing, and a pawl and ratchet, and manual means for advancing the cam shaft without affecting the timer by means of said pawl and ratchet, to adjust manually the time or length of defrost period.

12. In an automatic defrosting household refrigerator, the combination of an insulated cabinet having an insulated door, an evaporator in said cabinet having freezing coils and food storage cooling coils, a motor compressor, a condenser, and a capillary tube restrictor connected in series to said evaporator to form a closed circuit, a thermostatic switch controlling the operation of said motor compressor to maintain said freezing coils at a freezing temperature, an electric heater applied to the lowermost coils of said evaporator, an electric timer motor, a doorswitch which is closed by the opening of the door, said door switch being connected to said timer to integrate the time periods when the door is open and frost gathers on the evaporator, a cam driven by said timer motor and having a rise for actuating contacts, said cam opening refrigeration contacts connected to said thermostatic switch and compressor and closing heater contacts connected to said heater to initiate a defrost by heating refrigerant which circulates throughout the evaporator coils, when the total time of door openings reaches a predetermined amount, latching means for holding the heater contacts in closed position but biased to open position, and a thermostatic element for acting on said latch and releasing the heater contacts to move to open position responsive to a predetermined increase in evaporator temperature and to restore the closed circuit of the refrigeration contacts, said cam also controlling timer contacts connected to the timer motor and opening the timer contacts while the heater contacts are closed, and preventing the cycling of the timer by the opening of the door during defrost.

13. In an automatic defrosting household refrigerator, the combination of an insulated cabinet having an insulated door, an evaporator in said cabinet having freezing coils and food storage cooling coils, a motor compressor, a condenser, and a capillary tube restrictor connected in series to said evaporator to form a closed circuit, a thermostatic switch controlling the operation of said motor compressor to maintain said freezing coils at a freezing temperature, an electric heater applied to the lowermost coils of said evaporator, an electric timer motor, a door switch which is closed by the opening of the door, said door switch being connected to said timer to integrate the time periods when the door is open and frost gathers on the evaporator, a cam driven by said timer motor and having a rise for actuating contacts, said cam opening refrigeration contacts connected to said thermostatic switch and compressor and closing heater contacts connected to said heater to initiate a defrost by heating refrigerant which circulates throughout the evaporator coils, when the total time of door openings reaches a predetermined amount, latching means for holding the heater contacts in closed position but biased to open position, and a thermostatic element for acting on said latch and releasing the heater contacts to move to open position responsive to a predeterminedincrease in evaporator temperature and to restore the closed circuit of the refrigeration contacts, said cam also controlling timer contacts connected to the timer motor and opening the timer contacts while the heater contacts are closed, and preventing the cycling of the timer by the opening of the door during defrost, said cam closing the timer contacts while the refrigeration contacts are closed, to be controlled by the opening of the door.

14. In an automatic defrosting household refrigerator, the combination of an insulated cabinet having an insulated door, an evaporator in said cabinet having freezing coils and food storage cooling coils, a motor compressor, a condenser, and a capillary tube restrictor connected in series to said evaporator to form a closed circuit, a thermostatic switch controlling the operation of said motor compressor to maintain said freezing coils at a freezing temperature, an electric heater applied to the lowermost coils of said evaporator, an electric timer motor, a door switch which is closed by the opening of the door, said door switch being connected to said timer to integrate the time periods when the door is open and frost gathers on the evaporator, a cam driven by said timer motor and having a rise for actuating contacts, said cam opening refrigeration contacts connected to said thermostatic switch and compressor and closing heater contacts connected to said heater to initiate a defrost by heating refrigerant which circulates throughout the evaporator coils, when the total time of door openings -on said latch and releasingthe heater contacts to move to open position responsive to a predetermined increase in evaporator temperature and to restore the closed circuit of the refrigeration contacts, said latter thermostatic means having a bulb located on the evaporator adjacent the electric heater to be quickly responsive to the source of heat, for preventing overheating of the evaporator.

15. Refrigeration apparatus of the type having a heat absorbing unit connected in a closed circuit with a heat dissipating unit, and in which the heat absorbing unit is disposed within an insulated space from which heat is to be removed, said apparatus comprising a cold control mechanism for controlling the operation of said apparatus in accordance with the temperature of said space, a heat source including an electric heating element for causing the temperature of said heat absorbing unit to be raised to a degree sufficient to melt any frost which may have collected thereon, a movable door for providing access to said insulated space, an electric switch mechanism having contacts connected in series with said electric heating element, timing means operable in response to the total elapsed time during which said door has been opened, for operating said switch mechanism to connect said heater contacts and initiate operation of said heat source, and thermostatic means responsive to a predetermined higher temperature of said heat absorbing unit for effecting movement of the same switch mechanism in the opposite direction, to break the circuit through said electric heating element for terminating operation of said heat source and for restoring the system to the control of the normal operation by said cold con trol mechanism, the said switch mechanism also including a contact connecting said timing means in circuit during normal operation of the refrigerating apparatus, and opening the circuit to said timing means while the heater contact is closed. 7

References Cited in the file of this patent UNITED STATES PATENTS 1,913,433 Doble June 13, 1933 2,064,396 Volpin Dec. 15, 1936 2,124,375 Phillips July 19, 1938 2,324,309 McCloy July 13, 1943 2,382,733 Marcy Aug. 14, 1945 2,459,083 McCloy Ian. 11, 1949 2,463,027 Frie Mar. 1, 1949 2,595,967 McCloy May 6, 1952 2,601,466 Thomas June 24, 1952 2,612,026 Hansen Sept. 30, 1952

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