US2123073A - Means for automatic defrosting of refrigerating systems - Google Patents

Description

July 5, 1938. c. w. BELL 2,123,073

MEANS FOR AUTOMATIC DEFROSTING OF REFRIGERATING SYSTEMS Filed April 50, 1932 v s Sheet- Sheet 1 IN VENT OR ATTORNEYS July 5, 1938. c. w. BELL 2,123,073

MEANS FOR AUTOMATIC nmmosnue 0F REFRIGERATING SYSTEMS Filed April 50, 19s2 e Sheets-Sheet 2 INVENTOR Our/e5 W Bell.

ATTORNEYS July 5, 1938. c. w. BELL J 3 5 MEANS FOR AU'fOMATIC DEFROST'ING OF REFR IGERATING SYSTEMS Filed April 30, 1932 6 Sheets-Sheet 3 INVENTOR Char/e5 W 56/! BY @Q A TTORNEYS y c.w. BELL 2,123,013

MEANS FOR AUTOMATIC DEFROSTING OFREFRIGERATfNG SYSTEMS Filed April 30, 1 932 6 Sheets-Sheet 4 ATTORNEYS [bar/es W Bell. m

July 5, 1938. cfw. BELL 2,

MEANS FOR AUTOMATIC DEFROSTING OF REFRIGERATING SYSTEMS Filed April 50, ,1932 6 Sheets-Sheet 5 INVENTOR Char/es W Bell ATTORNEYS July 5, 1938.

c. w. BELL MEANS FOR AUTOMATIC DEFROSTING OF REFRIGERATING SYSTEMS Filed Ap ril 30, 1932 6 Sheets-Sheet 6 l l ll ll l'l l l l l l llvl INVENTOR Char/es W Bell "MM- 4I7'0RNEYS' Patented July 5, 1938 UNITED STATES PATENT OFF-ICE MEANS FOR AUTOMATICDEFROST'ING OF REFRIGERATING SYSTEMS Charles w. Bell, Westfield, N. J.; Edythe H. Bell executrix of said Charles W. Bell, deceased Application April 30, 1932, Serial No. 608,531

15 Claims.

This invention relates to the defrosting of ecoling elements of refrigerating units or systems and more particularly to means for starting such defrosting automatically when the ice on the cooling element reaches a predetermined thickness and for stopping the defrosting when the ice is melted away to a predetermined thinness. In domestic and commercial refrigerating units or systems wherein the temperature in a confined space. such as the interior 'of an enclosed c'ompartment, box or case, is maintained, at a deflnite point or within narrow limits adiacent thereto, there gradually accumulates on such cooling unit a coating of'iceor frost which, if

ll it buiidsup to an excessive thickness, interferes with or-prevents satisfactory and proper action of the cooling unit in maintaining efficiently the desired predetermined temperature.

Particularly in domestic refrigerating systems,

the primary source of refrigerating effect, or the refrigerant suppiying means, is intermittently operated in accordance with the action of a suitable control caused to operate, for example, by variations of pressure within the system or variations of thetemperature in the compartmentor the space within which cooling is to be effected or of the cooling unit itself. Heretofore, irrespective of theparticular nature of the control. defrosting has been effected by manually stopping the operation of the refrigerant-supply-' ing means andleaving it in this condition until the ice coating has melted either completely or g to a desired degree of thinness. The usual instructionsare to effect the defrosting operation at regular fixed intervals but these intervals may well be varied for the convmience of the operator and in view of the varying rates of growth of the ice coating under various conditions.

An important object of the invention is to pro- 4o vide for automatic control of the defrosting operation in accordance with changes of condition in the refrigerating system which may be considered to include the cooling chamber as well as the closed system "in which the refrigerant cir- 45 culates. I

Another object of the invention is to provide,

' in connection with a refrigerating system auto-.

matically started and stopped in accordance with refrigerating conditions, for automatic starting 50 of a defrosting action when the ice on thecool-- ing element reaches a predetermined maximum thickness and automatic stopping of this operation when the ice reaches a predetermined degree of thinness.

.55 Another object of the invention relates to the provision ofmeans, adapted for use in connection with a system which automatically works ing the thickness of the ice on the cooling element just before the system prepares to start up after each rest period and preventing such starting if 16 the ice be found to have reacheda predetermined maximum thickness, but also for permitting such starting when the ice has melted to a predetermineddegree of thinness.

Another object relates to the use of a feeler 20 movable toward and from the cooling element of an intermittently operated -system,a control device for prevention or permitting the starting of the system, and operating means for normally actuating the feeler without operation of the 25 control device and for actuating the control device when the feeler is stopped by ice of a predetermined maximum thickness on the cooling element, said operating means being restored to normal operation upon completion of the defrost- 3o ing action.

Further objects of the invention are to provide defrosting means of which a substantial part is self-contained. and may readily be applied to any one of the different types of intermittently 35 operated machines. and to provide defrosting means which will be substantially free from interference, such as by ice on the cooling element. Preferably the defrosting control includes a feeler movable toward and from a=cooling eie- 40 -ment on which the ice collects, an operating or motor element moving in accordance with changes of conditions in the system, a device, such as a switcher valve, for preventing or permitting operation of the refrigerant-supply means, a device operable by the motor element of the control to reciprocate the feeler or to operate the switch device or valve device to prevent operation of the refrigerant-supply means, and yielding means normally preventing opening a of the switch device or closing of the valve device (whichever be used) but yielding when the feeler is checked in its" forward movement by engagement with a predetermined thickness of ice on the cooling unit and returning to normal posltion when the ice is melted to a predetermined thinness and permits the feeler to advance to a corresponding position. Preferably the device in-. terposed between the motor element of the control and the feeler and the shutoff device is adapted to operate either the feeler or the shutoff depending upon which offers the greater resistance. During ordinary operation the shutoff device is yieldably held against operation thus causing normal operating movement of the feeler which advances during rest or idle periods to a position corresponding with the starting condition of the main control and retracts during active periods of the refrigerant-supplying means. When, however, the movement of the feeler is prevented by engagement of the same with ice of a predetermined maximum thickness on the cooler the shutoff device is operated against such yielding resistance and the defrosting operation is started. Then, as the. temperature rises and other changes in condition occur, the condition of the shutofl device is changed further so as to delay the throwing out of the shutoff device. When the ice has been melted to a predetermined thinness and the feeler is advanced accordingly farther than in its normal operating movement, the shutoff deviceis thrown out of action.

Other objects and advantages will be apparent upon consideration of the following description and of the drawings, in which:

Fig. 1 is a diagrammatic view illustrating one embodiment of the invention as applied to arefrigerating system of the compression-expansion type in which intermittent action of the compressor and the action of the defrosting device are controlled by variations of pressure in the refrigerating system, the parts being shown in the positions assumed just after starting the reirigerating system for the first time or at the end of a defrosting operation;

Fig. 2 is a view similar to Fig. 1, but showing the parts in the positions assumed just before the compressor is shut off by the main control, thefeeler being at the rearward end of its normal operating path;

Fig. 3 is a view similar to Fig. 1, but showing the parts in the positions assumed just after the main control has started the compressor, the feeler being at the forward end of its normal operating path;

Fig. 4 is a view similar to Fig. 1, but showing the parts in the positions assumed after the auxiliary control has been operated, due to the stopping of the feeler during its forward normal operating stroke, to prevent starting of the compressor;

Fig. 5 is a view corresponding to Fig. 1, but illustrating control of the intermittent action of the compressor and control of the defrosting device in accordance with changes in temperature in the space cooled by the refrigerating system;

Fig. 6 is a diagrammatic view illustrating one embodiment of the present invention applied to a refrigerating system of the absorption type, both the intermittent action of the refrigerating system and the action of the defrosting means being controlled in accordance with changes in temperature in the space to be cooled; and

Fig. 7 is a sectional view illustrating one form of valve for control by the defrosting device for shutting oil the supply of gas to the burner of the absorption system.

Referring to Fig. 1, l designates a compressor from which a suitable refrigerant, such, for example, as sulphur dioxide, is forced past the check valve II to a condenser l2 in which the refrigerant heated during compression is cooled. From the condenser the refrigerant passes to a receiver or reserve reservoir l3 connected in a suitable manner, as by conduit M, with a cooling element or unit 15. Admission of the liquid refrigerant to the cooling unit or evaporator I! may be controlled by suitable means such as an expansion valve (not shown) and a float operated valve (not shown). From the cooling element or evaporator IS the expanded refrigerant is returned through a suitable conduit or pipe I6 to the compressor into which it is drawn past a check valve I'I designed to prevent return of the refrigerant into the suction line l6.

Preferably, the compressor is driven by an electric motor l8 which may be coupled directly to the compressor or indirectly as by means of reduction gearing (not shown). As here disclosed, the rotor of the motor is directly connected with a shaft [9 carrying a crank 20 which is connected with the piston of the compressor by means of a connecting rod 2|. Power for actuating the motor I8 is provided through a circuit 22 and intermittent action of the motor may be obtained during ordinary operation by means of a control 23 having a connection 24 with the receiver l3 and adapted to open the circuit 22 when the pressure in the receiver l3 equals or exceeds a predetermined value and to close the circuit 22 when the pressure in the receiver l3 drops to or below a predetermined pressure. Preferably, the circuit 22 is also provided with a hand switch 24a.

When the ice accumulates on the cooling ele ment l up to a predetermined thickness, it becomes necessary to defrost or remove ice from the cooling element. Heretofore, defrosting has been effected by manually shutting off the compressor and maintaining it in that condition until the ice has melted to a predetermined thinness. The present invention contemplates automatic defrosting of the cooling element, as by means for opening and closing the circuit 22 independently of the action of the control device 23. Such opening and closing of the circuit may be effected by a switch 25 including a fixed contact 26 and a movable-contact 2'I controlled by the automatic defrosting means, which may include a motor or actuating portion operated in accordance with changes in pressure in the receiver I3, a feeler 28 movable toward and from the cooling element IS, a device for controlling the switch 25, and means interposed between the motor element on the one hand and the feeler 28 and the switch operating device on the other hand, whereby the motor element normally acts to reciprocate the feeler but upon engagement of the feeler with ice of excessive thickness on the cooling element acts to open the switch 21.

Preferably such interposed means includes a closed system filled with substantially incompressible fluid, preferably a liquid having a boiling point above the'maxi'mum and a freezing point below the minimum temperature to which the device will be subjected in operation, and is provided with a Sylphon 29 for operating the feeler 28, a Sylphon 30 for controlling the switch- 25, and an actuating Sylphon 3| controlled by the motor element. Obviously, contraction of the Sylphon 3| will cause expansion of one or both of the Sylphons 29 and 30, and expansion of the Sylphon 3| will cause contraction of one or both of the Sylphons 29 and 30. It will be understood that one end of each of the Sylphons 29, 30 and 3| is normally held in fixed position and that the other end is in each case left free for movement with respect to the fixed. end. The feeler 28 is connected with the free end of the Sylphon 23 and preferably consists of a plate or disc 32 to' engage the ice and a rod 33 extending axially with respect to the disc 32 to the free end of said Sylphon 29 to which it is secured so as to extend perpendicularly therefrom. Preferably the plate 32 and also the rod 33 are composed of material having a low thermal conductivity, for example, hard rubber or fibre.

' The Sylphon 29 may be supported at its inner end on a bracket 34 adjustably mounted on a fixed support 35 by means of a bolt or screw projecting through a slot 31 in the baseof the bracket. This enables the Sylphon 29 to be ad-' justed toward and from the cooling element l5 to adjust the position of the feeler with relation thereto. 'The'inner end of the Sylphon 38 may be mounted on a bracket 38 fixedly secured on a support 39, the outer end of the Sylphon 38 having fixed thereto the movable member2l of the switch 25'which is normally kept closed by yielding pressure exerted on the outer. head or end of the Sylphon 38, as bymeans of a spring 40 of suitable strength interposed between the outer end of said Sylphon 38 and a fixed member such as abracket 4| secured in fixed position on the support 39. The inner end of the Sylphon 3| may alsobe supported by a fixed bracket 42 preferably fixed on a fixed support 43.

The closed system containing the Sylphons 29, 30 and 3| may also include a pressure conduit or pipe 44 connecting Sylphons 29 and 3| and a conduit 45 connecting conduit 44 with Sylphon 30. It will be evident there must be some flexibility between Sylphons 29 and 3| to enable adjustment of bracket 34 while bracket 42 remains stationary. This flexibility may be obtained in various ways-{or example, by providing conduit 44 with an expansion coil or loop 46 which-also prevents interference with pipe or conduit 45.

In carrying out the present invention, the arrangement should be such that the feeler 28 would be advanced as the system approaches a condition for again starting the compressor and retracted as a result of such restarting, and that upon contact of the feeler during its forward movement with ice of excessive thickness the auxiliary control 'or switch 25 would be operated Just before the system reaches the condition to cause action by the control 23 to start up the compressor.

If the defrosting is to be controlled by pressure conditions, the feeler, 32 should be advanced as the pressure decreases in the pressure or high side of the system. This may be done by connecting the pressure line 24 fixedly mounted on the fixed support 58. For

by a branch 41 with the adjacent end of a Sylphon 48, which end is carried on a bracket 49 connection with the Sylphon 3 I, the other end of.

'this Sylphon may be provided with a rod 5| guided ina bracket 52 secured to a fixed support 53 and pivotally connected with one end of a lever 54 centrally pivoted at 55 andpivotally connected at its other. end with a rod 58 attached to the free and outer end of the Sylphon- 3|.

It will be evident that, with this arrangement,

a drop in pressure in the receiver l3 and connection 24 will tend to contract the Sylphon 43 and through the lever 54 compress the Sylphon 3|. This would ordinarily expand the Sylphon 28 and advance the feeler 28' toward the cooling element ii. If the ice on the cooling element had not reached the predetermined thickness the feeler would merely advance to the forward end of that movement determined by the low pressure at which the main control acts to start the compressor l8.

When the feeler 'is thus advanced to the end of its normal movement without striking the ice on the cooling element there is no need for defrosting and the switch 25 remains closed.

The pressure in the receiver and, its connection to the control 23 falls until this control is operated to start the compressor ill, the action of which continues" until the pressure in the re-' ceiver i3 reaches the predetermined. degree whereupon the control 23 is again operated tostop the motor l8. During this building up 1 of pressurevthe feeler 28 has been retracted to its rearward position determined by a spring 62 interposed between the bracket 52 and the free end of the Sylphon 48. This spring may be of such strength and characteristics as to provide for a range of movement of the Sylphon 48 requisite for the proper operation thereof under variations of pressure to which it is subjected in operation.

This spring 62 also assists in contracting or collapsing the Sylphon 48 when the pressure in the receiver falls and helps to overcome the spring 48 and the resistance of the Sylphon 30 and open the switch 25 when the feeler 28 engages ice of the predetermined maximum thickness on the cooling element l5.

The operation of the apparatus is substantially as follows: During operation of the compressor, pressure is built up in the receiver l3 until it reaches the predetermined maximum at whichthe main control 23 acts to open the circuit 22 and stop the motor l8 and the compressor l8. Then the pressure in the receiver i3 gradually drops as the liquid passes therefrom to the cooling unit l5 until the pressure reaches the predetermined point at which the main control 23 is set to restart the motor and the compressor. The Sylphon 48, is, of course, subjected to the same internal pressure as the receiver i3 and expands against the action of the spring 52 as the pressure increases and contracts when the pressure falls. This Sylphon 48 is so constructed and designed and the spring 62 is of v Due to the connection between Sylphon and movable contact 21 will be in engagement with fixed contact 28 at the switch 25. Fig. 2.)

(See

Following the stopping of the motor l8 by the main control 23, the pressure in the receiver falls, causing contraction of the Sylphons 48 and 3| and tending to expand the Sylphons 29 and 30. Expansion of the Sylphon 38, however, is resisted by the spring 48 so that the only expansion is that of Sylphon 29 and the feeler 28 is advanced toward the cooling element I5. Thus, if advance of the feeler 28' is not opposed during the contraction of Sylphon 43 caused by the drop in pressure to the point at which the main control 23 restarts the compressor, contacts 26 and 2i will remain in engagement with each other and the control 23 will restart the motor and the compressor in the usual manner, thus serving to retract the feeler 28 from the forwardend of its normal operating path. This intermittent operation of the compressor will continue until the ice 63 on the cooling unit reaches the predetermined maximum thickness (Fig. 4) to operate the defrosting means.

The Sylphon 29 is so positioned by adjustment of the bracket 34 that, when the pressure in the receiver i3 has fallen to the point where the main system control 23 would normally start the compressor, the corresponding condition of expansion of the Sylphon 29 would cause positioning of the disc 32 of the feeler 28 at such a distance from the cooling element l5 as to cause the disc to strike the ice coating 62, if the ice be of the maximum thickness desired, somewhat before the condition for starting the compressor is reached. Then since further movement of the feeler and expansion of the Sylphon 29 are prevented before the normal contraction of Sylphons 48 and 3] is completed, the further contraction of these Sylphons will cause the expansion of Sylphon 30 against the action of spring 40 and opening switch 25, thus preventing starting of the motor by the main control 23.

The fall of pressure in the receiver It will continue until the pressure throughout the main refrigerating system is equalized. This fall in pressure will tend to cause further contraction of Sylphons 48 and 3| and further expansion of Sylphon 30 until contraction of Sylphon 48 is checked by engagement of the hooked lug 51 on the free end thereof with the adjustable bracket or stop 58 which is so adjusted that the feeler disc 32 will have advanced to a point short of that corresponding with the minimum thinness (Fig. 1) of the ice coating for defrosting suiiicient to permit the Sylphon 30 in) contract under the influence of the spring 40 to bring the contact 21 into engagement with the contact 28, thus closing the switch 25 and restoring the motor I 8 to the control of the main control 23. It will be seen that during the defrosting operation the disc 32 of the feeler 28 will continue to be pressed against the surface of the ice coating and will advance as such surface recedes, due to the pressure exerted by the spring 40, until the Sylphon 30.

reaches its full allowable degree of contraction and causes closing of the switch 25.

It should be noted that the Sylphon 30 with the spring 40 cooperating therewith has three functions: (1) to open and close the switch 25; (2) .to supply the pressure to expand the Sylphon 29 and advance the feeler 28 after Sylphons 48 and 3| have reached their maximum degree of contraction; and (3) to limit the maximum possible pressure in the closed system containing the Sylphons29, 30 and 3|. This limitation of pressure is necessary in view of the fact that ice will melt under heavy pressure and excessive pressure of the disc 32 against the coating of ice on the cooling element would cause faster melting of the ice opposite the feeler than at other points thus causing the restarting of the compressor before the cooling element is suitably defrosted.

' It should also be noted that the disc 32 of the feeler 28 cannot be frozen to the surface of the ice coating on the cooling element and thus interfere with proper operation, in that the disc does not come into contact with the surface of the ice coating during normal operation and, when it does engage the ice, the defrosting device is caused to operate to produce defrosting or melting of the coating. Furthermore, as soon as the ice has been melted to the predetermined degree of thinness (Fig. 1)- the compressor H3 is started and immediately acts to increase the pressure in the receiver l3 and withdraw the disc from the cooling element l5 before any substantial effect to freeze it fast to the cooler can be produced by the refrigerating or freezing action which is resumed as soon as the compressor starts.

' During the defrosting operation the water resulting from the melting of the ice coating on the cooling element l5 will drip therefrom. Obviously, it will be necessary to arrange for the disposal of this drainage water as, for example, by the use of a drip pan normally supported under the cooling element and removable for emptying.

While the motor element of the defrosting device which has just been described is actuated by the variation in pressure in that part of the refrigerating system which is on the discharge side of the compressor, commonly known as the high side" of the system, it will be understood that the motor element may be actuated by the variation in pressure in that part of the refrigerating system which is on the suction side of the compressor, commonly known as the low side" or suction side" of the system. It will be understood that in such case the device is so arranged that an increase of pressure in the low side of the refrigerating system will move feeler toward the cooling unit and a decrease in pressure in the refrigerating system will withdraw feeler from cooling unit. In other words, Sylphon 48 will be so connected to Sylphon 3| as to cause contraction of Sylphon '3l when Sylphon 48 expands and to cause expansion of Sylphon 3| when Sylphon 48 contracts, and stop 58 and hook 51 will be so 7 arranged as to limit or stop the expansion of when the temperature in the compartment to be cooled or of the cooling unit itself drops to a predetermined minimum and to close the motor circuit when the temperature rises to a predetermined'maximum. The only feature by which the defrosting device of Fig. 5 diiIers substantially from that of Fig. 1 resides in the inclusion of a thermostatic device in the means for controlling the Sylphon 3| and the omission of any control by variations of pressure in the receiver.

The thermostatic device disclosed for purposes of illustration is in the form of a bimetallic strip 65 secured at one end to a fixed member; and pivotally connected at its other end with a con-. necting rod or link 61 which is' pivotally connected'with a member or rod 56a secured to the free end of the Sylphon 3| and positioned substantially axially with respect thereto. In order to limit the contraction of the Sylphon 3i and the advance of the feeler 22, the rod 56a may be in the base of the bracket. in order to avoid excessive stresses and possible breakage when the bimetallic strip 85 tends to advance the rod fur-- ther than the position determined by the adjustable stop 58a, suitable provision for yielding is made in the train of connections, as by connecting the adjacent end of the connecting rod 61 with the rod 56a by pivotally connecting the former with a block l0, mounted to slide in a slot in the end of the rod and normally held at the outer end of the slot by means of a helical spring 12 interposed between the block and the other end of the slot. The operation is substantially the same as described in connection with the apparatus sl'iown in Fig. 1.

In-Fig. 6, there is illustrated an application of a thermostatically controlled defrosting device to an absorption system. The defrosting device may be of any suitable form but for convenience is illustrated as being the same as that disclosed in Fig. 5 except that it-is utilized to control the supply of gas to a burner of anabsorption system which may be of any suitable form but for convenienceds illustrated as being of Munsters- Platen type shown'and described on pages 252 to 258, inclusive of The Handbook of Refrigerating Engineering" by W. R. Woolrich, published by D. Van Nostrand Company, Inc., New York, N. Y., 1929. The absorption system here shown includes an evaporator .15, an absorber 16 having a wateriacket, and a connection 11 between the upper part of the absorber and the upper part of theevaporator. At the time of manufacture of the apparatus, hydrogen at a suitable pressure,

150 pounds absolute for example, is sealed in the system and occupies the upper part of the evaporator, the upper .part of the absorber and the connectingpiping or connection 11.- Therefrigerant used is ammonia originally in the form of aqua ammonia located between the inner and outer walls of an annular tubular generator 18 which may be heated by a gas burner 19 at the bottom thereof.

there are formed ammonia gas bubbles which carry globules of rich liquor up the thermo- Sylphon tube "a to the top of the generator.

The ammonia gas from the generator is passed through a rectifier (not shown) where some cooling takes place, the liquid aqua ammonia separating out and draining back to the generator and the dry ammonia gas passing through a condenser 80' which may be of the double tube type with coolingwater'passing between the two' tubes. Theammonia thus condensed flows from the condenser into the evaporator "where it vaporizes justfast enough to nearly balance the pressures in the generator and the evaporator, in that too rapid evaporation will raise the pressure in the evaporator I5 and prevent the flow of ammonia to the same.

As the condensed ammonia evaporates in said evaporator, it diffuses with the hydrogen there present and'the' diffused gas being heavier than hydrogen will fall to the bottom of the evaporator and pass therefrom through a pipe M to the bottom of the absorber I8 which is .at a lower level. The ammonia here combines with weak liquor entering the absorber thus releasing hydrogen which goes to thetop of the absorber and forming strong liquorwhich passes back to the generator through a pipe 82 which forms the inner tube of a double tube 83 through the outer part of which passes in the opposite directionweak liquor received from a.pipe 84 connected with a higher point of the generator and discharged through a pipe 85 extending upwardly in the water jacket of the absorber to the upper part ofthe absorber proper. The cooling water is supplied through a pipe 86 which communicates with the lower part of the water jacket of the absorber and passes from this water jacket to the outer tube of the condenser 80 from which it is discharged through a pipe 81.

The flow of gas to the burner 19 may be shut off automaticallyby a' main thermal control 86 associated with the gas supply line 81, when the temperature drops too low, and turned on automatically when the temperature rises to a predetermined degree, the relighting of .the burner being, effected by means of a pilot light 88. The defrosting device is just the same as that shown in Fig. 2 except that the Sylphon 30 acts through a member Z'Iasecured to the free end thereof to close a quick-acting valve 89 when the ice on the cooling element or evaporator reaches a predetermined thickness, and to open the valve when the ice is melted to a predetermined thinness.

As shown in Fig. '7, the valve 89 maytake the form of a flat casing to which sections of the pipe or line 81 are connected at the opposite flat faces and the opening or closing of the valve may be effected by means of a member 9!! inside the casing at the discharge side thereof and pro vided with an opening 9| which'registers with the outlet opening of the casing when the member or slide is held in its raised position by a memher. or link 92 passing through the upper part of the casing and pivotally connected with the member 21a. When the Sylphon 30 is expanded due to engagement of the feeler with ice of a maximum thickness on the cooling element or evaporator 15, the slide 90 will be lowered sufllciently to close the outlet of the casing of the valve 89.

The slide 90 may be kept in close engagement with the outlet face of the casing by suitable means such as a bow spring 93 having one end fastened to the opposite side of the casing and the other end free but resting against the same side of the casing. It should be understood that the spring 93 does not cover theopening 9i in the slide 90 when the latteris in its Fig. 7 position but is at one side of the opening.

circumstances but would be closed when it was desired to assure continuance of the usual refrigcrating action without defrosting. It will be evident that switch 240. provides for throwing the whole system out of operation or for starting it.

In the absorption system shown in Fig.6 maintenance of normal operation may be assured, regardless of conditions which would ordinarily cause defrosting by providing a by-pass around the defrosting-control valve 89 and a valve 95 to control the by-pass. When valve 95 is open, the defrosting unit cannot produce defrosting.

This system may also be provided with a' valve 96 in the fuel line 81 adapted, when closed, to shut down the entire system.

It should be understood that the present invention is applicable to refrigerating systems of other types than those disclosed and that, although it is desirable'to use a pressure-operated motor element for a defrosting device used with a refrigerating system controlled in accordance with pressure therein and to use a thermostatic motor element when the main control is thermostatic,'it is not necessary to do so.

The foregoing detailed description has been given for clearness-of understanding and no undue limitation should be deduced therefrom, but the appended claims should be construed as broadly as possible in view of the prior art.

Having thus described my invention, I claim: 1. The combination with a refrigerating system including a cooling element, means for supplying refrigerant to said cooling element in condition to cool the same and controlling means for starting and stopping the operation of the refrigerant-supplying means in accordance with changes of condition in connection with said sys tem, of defrosting means including an auxiliary control for preventing or permitting operation of the refrigerant-supplying means, a closed system containing a suitable fluid and having at one point a movable part adapted to exert pressure in the closed system, a second movable part movable toward or from the cooling element in accordance with increase or decrease of pressure exerted by movement of the first movable part and a third movable part movable outwardly and inwardly in accordance with increase or decrease of pressure exerted by movement of the first movable part, a feeler connected with the second movable member, a connection between the third movable part and the auxiliary control, and yielding means tending to prevent movement of the third movable part but movable upon engagement of the feeler with ice of excessive thickness on the cooling element to prevent operation of the refrigerant-supplying means, and acting upon melting of the ice to a predetermined thinness to restore the refrigerant-supplying means to the control of said controlling means. 2. The combination with a refrigerating system including a cooling element, means for supplying refrigerant to said cooling system in condition to cool the same and controlling means for starting and stopping the operation of the refrigerantsuppiying means in accordance with changes of condition in connection with said system, of defrosting means including an auxiliary control 'for preventing or permitting operation of the refrigerant-supplying means, a closed system filled with a suitable liquid and including three interconnected Sylphons with their inner ends held in fixed positions, a feeler connected with the outer end oi one'of said Sylphons for movement thereby toward and from the cooling element, means connected with the outer end of comes into engagement with a layer of ice of preincluding a compressor, a condenser, and a cooling element to which the condensed refrigerant is supplied, compressor-actuating means and a pressure-operated main control for said compressor-actuating means connected by a pressure line with the refrigerating system of an auxiliary control for preventing or permitting operation of the compressor-actuating means, a feeler movable toward and from said cooling element, a closed system containing a suitable liquid and including three Sylphons fixed at their connected inner ends and having their outer ends movable to permit expansion or contraction, saidSylphons including one connected with the auxiliary control to operate the same, a second one connected with the feeler to operate the same and a third or actuating Sylphon operated to expand and contract the others, pressure means connected with said pressure line for contracting and expanding said actuating Sylphon in accordance with changes of pressure in said pressure line, and

' yielding means normally preventing expansion of the auxiliary-control-operating Sylphon.

4. The combination with a refrigerating system including a compressor, a condenser, and a cool,- ing element to which the condensed refrigerant is supplied, compressor-actuating means and a pressure-operated main control for said compressor-actuating means connected by a pressure line with the refrigerating system, of an auxiliary control for preventing or permitting operation of the compressor-actuating means, a'feeler movable toward and from said cooling element, a closed system containing a suitable liquid and in cluding three interconnected Sylphons fixed at their connected inner' ends and having their outer ends movable to permit expansion or contraction, said Sylphons including one connected with the auxiliary control to operate the same, a second one connected with the feeler to operate the same and a third or actuating Sylphonoperated to expand and contract the others, yielding means normally preventing expansion of the auxiliary-control-operating Sylphon, and means for expanding and contracting said actuating Sylphon in ac cordance with change of pressure in said pressure line including a fourth Sylphon connected at its inner fixed end-with said pressure line and connections between the outer end of the fourth Sylphon and the outer end of the actuating Sylphon whereby they act in unison.

5. The combination with a refrigerating system including a compressor, a condenser, and a cooling element to which the condensed refrigerant is supplied, compressor-actuating means and a pressure-operated. main control for said compressor-actuating means connected by a pressure line with the refrigerating system between the condenser and the cooling element, of an auxiliary control for preventing or permitting operation of the compressor-actuating means, a feeler movable toward and from said cooling element, a closed system containing a suitable liquid and including three interconnected Sylphons fixed at their connected inner ends and having their outer ends movable to permit expansion or contraction, said Sylphons including one connected with the auxiliary control to operate the same, a second one connected with the feeler to operate the same and a third or actuating Sylphon operated to expand and contract the others, yield- .ing means normally preventing expansion of the auxiliary-control-operating Sylphon,means for opcrating said actuating Sylphon in accordance with between the outer end of the fourth Sylphon and the outer end of the actuating Sylphon whereby they act in unison, and yielding means resisting the expansion of the fourth Sylphon, thereby tending to limit the rearward movement of the feeler and to assist in advancing the feeler and operating the auxiliary control.

6. The combination with a refrigerating system including a compressor a condenser, and a cooling element to which the condensed refrigerant is supplied, compressor-actuating means and a pressure-operated main control for said compressor-actuating means connected by a. pressure line with the refrigerating system,'of an auxiliary control for preventing or permitting opera ation of the compressor-actuating means, a feeler movable toward and from said cooling element, a closed system containing a suitable liquid and including three interconnected Sylphons fixed at their connected inner ends and having their outer ends movable to permit expansion or contraction,

said Sylphons including one connected with the auxiliary control to operate the same, a second one connected with the feeler to operate the same and a third or actuating Sylphon operated to expand and contract the others,yielding means normally preventing expansion of the auxiliarycontrol-operating Sylphon, means for varying the capacity of said actuating Sylphon with rise and fall of pressure in said pressure line including a fourth Sylphon connected at its inner flxedend- 'with said pressure line, yielding means resisting the expansion ofsaid fourth Sylphon, connections between the outer end of said fourth Sylphon and the, outer end of said actuating Sylphon to cause them to act in unison, and means'for limiting the movement of said fourth Sylphon to limit contraction of the third Sylphon.

7. The combination with a refrigerating system including a compressor, a condenser, and a cooling element to which the condensed refrigerant is supplied, compressor-actuating means and a thermostatic main control for said compressoractuating means, of an auxiliary control for preventing or permitting operation of the compressor-actuating means, a feeler movable toward and from said cooling element, a closed system containing a suitable liquid and including three actuating Sylphon, and means for limiting interconnected Sylphons fixed at their connected inner ends and having their outer ends movable to permit expansion or contraction, said Sylphons including one connected with the auxiliary control to operate the same, a second one connected with the feeler to operate the same and a third or actuatingv Sylphon operated to expand and contract the others, yielding means normally preventing expansion of the auxiliary-controloperating Sylphon, means for expanding and contracting said actuating Sylphon including a thermostatic device,' and a connection between said thermostatic device and the outer end of the the contraction of the actuating Sylphon. I 8. The combination with a refrigerating system including a compressor, a condenser, and a cooling element to which the condensed refrigerant is supplied, compressor-actuating means and a thermostatic main control for said compressor-'- actuating means, of an auxiliary control for preventing or permitting operation of the compressor-actuating means, a feeler movable toward and from said cooling element. a closed system containing a suitable liquid and including three interconnected Sylphons'fixed at their connected inner ends and having theirouter ends movable to permit expansion or contraction, said Sylphons including one connected with the feeler to operate the same and a third or actuating Sylphon operated to expand and contract the others, yielding means normally preventing expansion of the auxiliary-control-operating Sylphon, means for expanding and contracting said actuating Sylphon'including a thermostatic device and a connection between said thermostatic deviceand the outer end of the actuating Sylphon, said connection being strong enough to expand and collapse said actuating Sylphon but yieldable to prevent damage when contraction of such Sylphon is blocked, and a stop device to check the collapse of the actuating Sylphon, thereby causing said connection to yield.

9. The combination with a refrigerating system of the absorption type including a cooling element, a generator, a burner, a fuel supply line for said burner, a main control of the thermostatic type for opening and shutting the supply line in accordance with the demands of the system, and a pilot connected with said supply line at the entrance side of the main control, of an auxiliary control in said supply line for closing and opening the supply line thereby preventing or permitting heating of said generator, a feeler movable toward and from said cooling element, a closed system containing a suitable liquid and'including static device and the outer end of the actuating Sylphon, said connection serving to actuate the feeler or the auxiliary control when the feeleris blocked and yielding when contraction of the actuating Sylphon is prevented, and a stop device to limit the collapse of the actuating Sylphon.

10. The combination with a refrigerating system including a compressor, 'an electric motor for operating said compressor, a circuit to supply power to said motor, a condenser, a cooling element, and a pressure-operated main control connected with the interior of the refrigerating sysso I tem and adapted to open said circuit and close said tem including a compressor, an electric motor for operating said compressor, a circuit to supply power to said motor, a condenser, a cooling element, and a thermostatic main control adapted to open said circuit and close said circuit when the temperature reaches predetermined limits, of an auxiliary control for the compressor-actuating means including a second-switch in said circuit, a feeler, thermostatic means for moving, during normal operation of the refrigerating system, the feeler toward said cooling element while the compressor is idle and from said cooling element when the compressor is working, and 'for opening and closing said second-switch at other times, yielding means tending to hold said switch closed, and a manually controlled switch in parallel with said second-switch. I

12. The combination with a refrigerating system of the absorption type including a cooling element, acondenser from which refrigerant is supplied to said cooling element, a generator, a burner, a fuel supply line for said burner, a thermostatic main control for opening and closing the supply line in accordance with the demands of the system, and a pilot light connected with said supply line at the entrance side of the main control, of an auxiliary control in said supply line, a feeler, means for moving the feeler towards said cooling element when the temperature thereof is falling and from the cooling element when the temperature is rising or for opening and closing said auxiliary control, yielding meansnormally holding the auxiliary control against closing but permitting it to close when the feeler is stopped by ice on the cooler before it reaches the end of its normal operating stroke, and manually controlled means ior supplying fuelpast said auxiliary control. a

13. In defrosting apparatus for a refrigerating system embodying a cooling element, the combination of a pressure motor device, a feeler operatively associated therewith and having a predetermined normal range ofmovement, a refrigeration control device and means, operable upon checking of the feeler short of its normal range of movement, to actuate said control device.

14 In defrosting apparatus ior a refrigerating system embodying a cooling element, the combination of a thermostatic motor device, a feeler operatively associated therewith and having a predetermined normal range of movement, a refrigeration control .device and means, operable upon checking of the feeler short of its normal range of movement, to actuate said control device.

15. In defrosting apparatus for refrigerating systems, the combination of a reciprocating feeler, an electric circuit control device, a closed system containing a suitable liquid and including three interconnected Sylphons normally fixed at their connected ends and having their opposite ends movable to permit expansion or contraction, said Sylphons including one connected with the control device to operate the same, a second one connected with the feeler to operate the same, and a third or motor Sylphon operated to expand and contract the others, and yielding means normally preventing expansion of the control-device-operating Sylphon but permitting such expansion upon interference with the movement of the feeler du to the accumulation of ice.

CHARLES W. BELL.

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