US2463027A

US2463027A - Refrigeration apparatus arranged for periodic defrosting

Info

Publication number: US2463027A
Application number: US581804A
Authority: US
Inventors: Frie George
Original assignee: Kramer Trenton Co
Current assignee: Kramer Trenton Co
Priority date: 1945-03-09
Filing date: 1945-03-09
Publication date: 1949-03-01
Anticipated expiration: 1966-03-01

Description

March 1, 1949.

INVENTOR. m

- G. FRIE REFRIGERATION APPARATUS ARRANGED FORPERIODIC DEFROSTING Filed March 9, 1945 0 own 00 U300 Patented Mar. 1, 1949 REFRIGERATION APPARATUS ARRANGED FOR PERIODIC George Frle, Trenton, N. J., assignor to Kramer Trenton, N. J., a corpora- Trenton Company, tion of New Jersey DEFROSTING Application March 9, 1945, Serial No. 581,804 14 Claims. (01. 62-4) This invention relates to refrigerating apparatus and, more particularly, to the provision in such apparatus of means for automatic periodic defrosting of the evaporating or chilling unit.

It is well known that refrigerating apparatus. particularly if designed for creating temperatures below freezing, when in operation accumulates a layer of ice on the coil of the evaporating or chilling unit. This accumulation of ice reduces the operating efliciency of the apparatus so seriously as to require periodic removal of the ice, which step is known in this art as defrosting." In the past, this defrosting has commonly been left to the activity of an attendant who initiated the same at more or less regular intervals by the manual operation of a switch or valve for melting the ice by the action of electricity or tap water, or in some other appropriate manner. This procedure necessarily involved the disadvantages which inevitably arise when the performance of a step is left to operational attention instead of being automatically performed by suitable mechanism or device, with the result that, in many cases, refrigerating apparatus has frequently, if not generally, been operated with a degree of efficiency far below its designed and desired capacity.

The difiiculty arising from the icing up of the evaporator unit is very pronounced in the compact, unit type of refrigerating apparatus where-' in the parts of the coil are close together and the fins on the coil are closely spaced, because this small clearance between coil and fins accelerates the pace at which the ice accumulates and thereby gives rise to decreases in efficiency of operation at frequent intervals.

Application for United States patent filed by Israel Kramer on November 7, 1944, under Serial No. 562,299, now Patent No. 2,440,146, granted April 20, 1948, discloses the defrosting of the coil of the evaporator unit of refrigerating apparatus by automatic action which becomes effective at regular and predetermined intervals, thus eliminating to a large extent the above recited previously existing disadvantages and others inherent .in conditions arising from the icing up of the evaporator unit; and my invention contemplates a further advance in the same general direction by providing not only for automatic defrosting of the coil but also for automatic regulation of the times at which the defrosting step takes place so as to insure the accomplishment of this function whenever required by operating conditions while, at the same time, obviating the unnecessary or untimely performance of the said function. My invention is herein shown as applied to the apparatus disclosed in the above named application of Israel Kramer, Serial No.

-562,299, but it is also applicable to any other refrigerating apparatus of the compressor type which includes means fOr defrosting the evaporator unit following the accumulation of ice thereupon.

It is well known that the conditions under which refrigerating apparatus performs vary to a substantial extent during the hours of a twenty-four hour day, or even of a shorter day, as well as with seasonal changes and atmospheric and temperature changes within seasons. For instance, during the working day, the room or space chilled by the apparatus is apt to be loaded with comparatively warm substances, to have electric lights therein turned on, to have operatives working therein, to have its door opened and closed at frequent intervals, etc. etc. During the night hours on the other hand, when the plant in which the apparatus operates is idle or themarket is closed, the above named factors do not obtain or, at least, are not present to nearly as great an extent. Similar variations in the de mands or loads upon the refrigerating apparatus occur during substantial temperature and atmospheric changes and, especially, from season to season.

The result of these varying operative conditions is that the evaporator unit of the refrigerating apparatus accumulates ice much more rapidly during working hours and under conditions of high temperature and/or humidity, with the concomitant of much more frequent demand for defrosting of the said unit in order to maintain the apparatus at or near peak efficiency. It will therefore be evident that an arrangement of such a refrigerating apparatus or system in which defrosting takes place at fixed intervals can be neither fully responsive to all operational requirements nor ideally suited to functioning with the highest degree of economy. This is so, if for no other reason, because the predetermination and fixing of equally spaced periods of defrosting is liable either to provide an inadequate number of defrostings during the periods of heavy load upon the apparatus or provide an excessive number of defrcstings during the periods when the load is light. An inadequate number of defrostings during the heavy load periods would, of course, reduce the eiliciency of the apparatus as a refrigerating means; while an excessive num-- ber of defrostings during the light load periods would tend to uneconomical operation because accumulation of ice on each defrosting raises the temperature of the evaporating unit above that at which it is operative and imposes upon the apparatus a cooling- ,down or pull-down load in reestablishing operative temperature in the said unit and refrigerating chamber.

My invention overcomes or obviates the above recited, and other inherent, disadvantages in apparatus or systems of this character wherein defrosting occurs at fixed intervals, by associating the initiation of the defrosting function with the period of time that the compressor has been in operation; ically start when the compressor has been running for a predetermined period of time regardless of the actual time intervals between defrostings. It is, of course, well known in this art that the operation of the compressor is intermittent and that its running and stopping are determined by conditions in the refrigerating chamber. In other words, the compressor runs until the predetermined desired temperature in the chamber has been attained and then automatically stopped until the temperature in the chamber has risen a predetermined number of degrees, at which point-the compressor is again automatically started. From this it will be clear that the compressor will naturally operate much more continuously during periods of heavy load on the apparatus or system than during periods of light load so that, purely compressor may be in actual operation for one hour out of every hour and a half period during theheavy load of daytime, and for one hour out of every three hours during the light load of nighttime. Similar differences periods of the compressor may occur in accordance with seasonal changes and changes in temperature and humidity regardless of season.

If it be assumed that the temperature of the refrigerant in the evaporator unit is constant and that the temperature and humidity of the refrigerating chamber of ice accumulation on the coil will be substantially constant. This icing of the coil occurs only while the compressor is running because, when the compressor stops, the temperature of the refrigerant'rises. Therefore, with a given temperature of refrigerant and given temperature and humidity of the refrigerating chamber, the the coil is, for practical purposes, directly proportional to the duration of compressor operation. While there are, of course, variations in the factors of temperature and humidity just named, the stated relationship between compressor operation and ice formation is, on the average, precise for all practical purposes.

The apparatus of this invention includes means for totalling the durations of the intermittent periods of operation of the compressor and, each time the total equals an established number of hours and/or'minutes, automatically starting the defrosting; thus taking note and advantage of the said direct relationship between duration of compressor operation and amount of ice accumulation on the evaporator coil, and providing automatic defrostings in accordance with the actual extent of ice accumulation regardless of the time period required for the accumulation, in order to maintain efliciency and economy in the use of the apparatus or system under all load and climatic conditions.

An object of the invention is toprovide refrigcrating apparatus which includes means for autoso that each defrosting will automatin operating by way of illustration, the

are also constant, the rate fled form in which a pressure switch only;

oil sump 2, andv is driven by an which is connected thereto by a belt 4.

4 matlcally initiating defrosting whenever peak efiiciency under operating load demands, and omitting defrosting except when so demanded.

Another object consists in providing such an apparatus which includes means for automatically initiating defrostings and for automatically determining the time of such initiation and regulating the time periods therebetween.

Another object consists in providing refrigerating apparatus which includes means for automatically initiating defrosting whenever the accumulation of ice on the evaporator reaches a predetermined amount. I

Another object consists in providing such an apparatus which includes means for automatically initiating defrosting whenever the compressor has been in operation for a predetermined period.

Another object consists in providing such an apparatus which includes means for totaling the durations of the periods of compressor operation and initiating defrosting at each completion by the compressor of a predetermined amount of operation.

Another object consists in providing such an apparatus which includes means that operates concurrently with compressor operation and imcompletion by the compressor of a predetermined amount of operation.

Another object consists in providing such an apparatus which includes means for performing any' one or more of'the above named functions, saidmeans being in part controlled by a thermostatic device, a pressure device, or both; and in part by timing mechanism;

A further object consists in providing certain improvements in the form, construction, arrangement and material whereby the above named'and other objects may be effectively attained.

Practical embodiments of the invention are diagrammatically represented in the accompanying drawing, in which Fig. 1 represents the invention as applied to the refrigerating apparatus disclosed in the above named application for United States Letters Patent Serial No. 562,299, and includes both a pressure switch and thermostatic switch for controlling the intermittent operation of the compressor;

Fig. 2 represents a detail view of amodified form of the apparatus shown in Fig. 1 which includes a thermostatic switch only;

- Fig. 3 represents a view similar to Fig. 2-but showing a second modified form which includes and Fig. 4 represents a detail view of a third modithe arrangement is such that the fan motor of the evaporator unit does not stop when the compressor stops.

The apparatus includes a compressor, denoted by l, which may be'of any wellknown or approved form adapted for the compressing and supplying, in a manner well known to those skilled in this art. of any suitable refrigerating agent such, for instance, as ammonia gas, sulphur dioxide, methyl chloride, isobutane or Freon. I he compressor is preferably provided with the usual electric motor 3 the said coils, and

A pipe 5, commonly known as a suction pipe, supplies the gas to the intake of. compressor I, and another pipe 6, which is connected to the outlet of the compressor, carries the compressed gas therefrom to several parts of the apparatus. The said pipe 6 enters at the top of a- .vessel 1 that is located within a casing 8, is coiled in the bottom of the vessel as indicated at 9, and leaves the said vessel at the top thereof. The construction and functioning of the vessel I and associated parts are fully set forth in the above named application of Israel Kramer, Serial No. 562,299, and, as they form no tion, will not be further illustrated or described herein.

From the point at which the pipe 5 leaves vessel I, it follows a downward and lateral course to a condenser III which may be of any well known or approved construction that need not be described herein as it'is within the knowledge and practice of those skilled in this art. The condenser serves to liquefy the gas it receives from pipe 6 and the liquid then drops through a tube II into a receiver I2, which may also be of any well known or approved form familiar to this art.

From the receiver I2 the liquid, still under compression, passes through a pipe I3 to a thermostatic expansion valve I4, the construction and functioning of which are well known to those versed in the manufacture of refrigerating apparatus and call for no description herein. A pipe I5, which is shown asbroken for compactness in drawing, leads to the lower end of the coil I6 of an evaporator unit I1 which, again, may be of any well known or approved construction.

From the upper end of the said coil IS, a pipe I 8, also shown as broken, leads into the upper part of a tank I 9 located within vessel 1, to the top of which tank suction pipe 5 is connected; thus completing the circuit from the compressor I to the vessel 1, to the condenser III, to the receiver I2, to the expansion valve I4, to the coil I6 of the evaporator unit, to the tank I9 and back to the compressor.

A branch pipe is connected to pipe 5 at 2I and runs (though shown as broken) to a drip pan coil 22 that is set in the lower part of a housing 23 which surrounds the evaporator II, the said coil 22 being connected by a pipe -24 with pipe I5 that leads from thermostatic expansion valve I 4 to evaporator coil I6. A solenoid valve 25 is fitted in pipe 20, as is also a metering valve 25, which latter is located between the solenoid valve and the drip Dan coil 22. A shut-off valve 21 may be inserted in pipe I3 between receiver I2 and thermostatic expansion valve I4, if desired. By suitable adjustment of the metering valve 26, the supplying of an excessive amount of hot gas to the evaporator during defrosting can be prevented.

When the solenoid valve 25 is closed, no gas from the compressor I can pass to the drip pan coil 22 and thence through pipes 24 and I5 to the evaporator coil I6; but, when the solenoid valve is open, the hot gas from compressor I can take the course just described and thereby enter said coils in the form of a hot gas, instead of as a liquid which is the case when the gas from compressor I is caused to pass through condenser I0 and receiver I2. The hot gas thus entering coils 22 and I6 will serve to melt the ice collected upon more especially upon coil I5,

part of the present inven to be maintained in in suction pipe thus defrosting them and eliminating this deterrent to efficient operation.

It is important that this defrosting operation take place whenever the ice accumulation on the coils I5 and 22 attains such thickness or weight as materially to handicap the efficiency of the said coils; and it is also important that the successive defrostings be automatically initiated in order to eliminate the human equation element. As hereinbefore noted, the present invention embodies means for performing the functions just stated, which means will now be described.

Still referring to the form of the invention illustrated in Fig. 1, one wire 28 leads from a source of electric current (not shown) to one terminal of motor 3; while another wire 29 from the said source leads to one terminal 38 of a pressure switch 3|, the other terminal 32 of which is connected by a wire 33 with one terminal 34 of a thermostatic switch 35 that has its other terminal 36 connected by a wire 31 with the second terminal of motor 3. As a result of the arrangement just described, it will be seen that current is provided for driving motor 3, and hence for operating compressor I, whenever switches 3I and 35 are both closed, but that the opening of either or both said switches will break the circuit and cause the motor and compressor to cease operation.

A wire 38 leads from wire 28 through to one terminal of an electric motor 39 that is mounted on housing 23 and drives fan 48 which cooperates with evaporator coil I6 in a well understood manner. A branch wire 4I leading from wire 38 runs to one brush of an electric timer 42, and another branch wire 43 runs from wire 38 to one con- .nection of solenoid valve 25. A wire 44 leads from wire 31 to the pivotal contact 45 of a double switch 46; and a branch wire 41 connects wire 44 with the second brush of timer 42. A wire 48 runs from the second connection of solenoid valve 25 to one terminal 49 of double switch terminal 58 of said switch is connected by wire 5| with the second terminal of fan motor 39.

Thepressure switch 3l may be of any well known or approved form, sever-a1 of which are commercially available as units, and its bellows is connected by a capillary tube 52 with suction pipe 5, as indicated at 53, so that the operation of switch 3| will be subject to the pressure in pipe 5. The thermostatic switch 35 may likewise be of any well known and approved form, several of which are commercially available as units, and its bellows is connected by a capillary tube 54 with a feeler bulb 55 which may be conveniently located in the refrigerating chamber so as to be subject to variations in temperature in the chamber. It will thus be seen that when the pressure 5 reaches a predetermined low point, switch 3| will be opened, as indicated in dotted lines, thereby breaking the electric circuit to motor 3. Likewise, when the temperature in the refrigerating chamber reaches a predetermined low point, switch 35 will be opened, as indicated in dotted lines, and break the electric current to motor 3. It is desirable, under certain conditions, to utilize both these switches; and this is particularly true when the operative temperature of the refrigerating chamber is desired a low zone, e. g. below the frost line, because, in that zone, a thermostatic switch is more responsive to changes than a pressure switch. In other words, at low temperatures, changes intemperature of refrigerants. are accompanied by comparatively small changes in pressure which, generally speaking, makes a ther- 46, while the other der these conditions sented by levers 42*and 46' running. The timer said clock mechanism if, in a given apparatus or system,

mostatic switch more sensitive and reliable unthan a pressure switch. However, a, pressure switch is not only satisfactory under many temperature conditions, but it is also desirable as an auxiliary to the thermostatic switch especially for the purpose of preventing the compressor I from too greatly reducing the pressure in suction pipe 5, e. g., to the extent of approximating a vacuum. By the use of both switches, therefore, the apparatus accommodates itself to the widest range of conditions that may be demanded in the trade, and sensitivity and positiveness in action are insured.

As is well understood in this art, a relatively low pressure in suction pipe .5, which is in communication with pipe l8 that is connected to the outlet of evaporator coil l6, indicates that refrigerating conditions are temporarily satisfied so that the operation of compressor I may cease. Pressure switch 3| is therefore set to be operative at a predetermined pressure in pipe 5, whereupon it will break the electric current to motor 3 and stop compressor I. Similarly, when the temperature in the refrigerating chamber has reached the desired low point,'feeler bulb 55 will be responsive thereto and actuate switch 35. with the result of stopping compressor I. Hence, when predetermined refrigerating conditions have been reached in the refrigerating chamber, active operation of the apparatus ceases through actuation of switch 3| or switch 35, or both.

When, on the other hand, after a period of inactivity of the compressor, temperature conditions in the chamber and pressure conditions in the suction pipe 5 have risen to approximately of the compressor be for 8 the compressor runs for fifteen minutes and then stops, the timer will register or otherwiserespond to that period of time. If the next operation twenty-five minutes, the timer will total up forty minutes. Then, if the next operation of the compressor be twenty minutes or more, the timer will add the said twenty minutes to the fort minutes already accumulated and, at the sixty minute point will actuate the switch 46 so as to open the solenoid valve 25 and permit a defrosting to be initiated by passage of the hot gas through pipe 20 to coils 22 and It as hereinabove described. The timer also includes adjustable mechanism for determining the length of time the switch which is tripped or operated by its clock mechanism shall remain in tripped or changed position. Consequently, the manufacturer or the one who installs the refrigerating system can set the timer so as to establish inadvance the duration of each defrosting, e. g. fifteen minutes. It will be clear from the foregoing illustrative remarks that defrosting will be initiated each time the compressor has achieved a total operative duration of one hour and that each defrosting will be permitted to continue for fifteen minutes. These illustrative periods can be changed in either direction in accordance with the size, character,

. and operational requirements of the refrigeratmg apparatus and, once they have been appropriately and properly established, the operation of the apparatus or system will be automatic the upper limit permissible under the desired conditions of operation, the said switches will close and, by thus reestablishing the electric current from the source of supply to the motor 3,will restart the compressor.

The timer 42 may be any one of a number of commercial electric timers embodying clocklike mechanism which can be set so as to activate other mechanism at predetermined times. Several forms of such devices are on the market for sale as units so that it is deemed "unnecessary to describe their construction, though it may be said that, essentially, they include two electric circuits, one of which operates a synchronous motor to drive the clock mechanism, which mechanism, in turn, other electrical circuit so as to tuate some other device such as, in the present case, the solenoid valve 25 and the fan motor 39. Such a suitable operating connection between the timer 42 and the switch 46 is reprewith their connecting shaft which is shown asbroken to avoid interference with reference numerals. ing to this invention, the timer 42 is in and out of operation in correspondence ,with the compressor l, and the clock mechanism of the timer therefore runs only while the compressor is is set so that its clock mechanism will. accumulate the durations of the periods during which the compressor is in operation and, after this accumulation reaches a certain number of hours and/or minutes, the will trip or operate the switch 46 so as to affect the solenoid valve 25 and, if desired, the fan motor 39. For instance,

it be predetermined that defrosting should'take place whenever the compressor I has been in operation for an hour, the timer 42 will be so set. If, then,

cause it to acand the intervals between defrostings will. be in accordance with the load upon the apparatus as is reflected with accuracy by the amount of ice accumulation on the evaporator coils which is substantially directly in proportion to the duraspacing will vary all the way tion of operation of the compressor. Thus, when the apparatus is under heavy load, defrostings may succeed each other with great rapidity while, when the apparatus is under light load. defrostings will be widely spaced, and the said from the heaviest load through medium loads to the lightest load.

45 Referring more specifically to the elements and trips a switch of the '1 Accord,-

' electrical circuits exhibited in Fig. 1 of the drawings, the switches Hand 35 are shown in full lines .as closed and the switch 46 is shown in full lines as completing electrical connectionrbetween the source of current supply and the fan motor 39. With the parts in'this position, the current from the source of supply will pass through wire 28 on the one hand and through wire 29, switches 3| and 35, and wire 31, on the other hand, to the motor 3, which will drive compressor I through belt 4. As the circuit is also connected through fan motor 39, it will drive fan 40, and timer 42 will also be actuated; while solenoid valve 25 will remain closed because its wire 43 is not connected by switch 46 through to pivotal terminal 45. After the desired conditions within the refrigerating chamber in which the apparatus is installed have been attained, as reflected by the temperature in the chamber and/or by the pressure within suction pipe5, l8, either or both switches 3| and 35 will be opened to the.dotted position shown in Fig. 1, whereupon motor 3 and compressor l, motor 39 and fan 49, andtimer 42 will stop. The clock mechanism in thetimer, however, has registered the amount of time during which compressor I has been in operation. When, now, conditions within the refrigerating chamber have reached the point calling for renewed activity of the ap- 3| and 35 will be closed so as to complete the electric circuit to motor 3 and again start it and compressor in operation, together with fan motor 39 and timer 42. This procedure will continue until timer 42 has accumulated or registered the predetermined duration of operation of compressor I, in either its intermittent or continuous activity, calculated to call for defrosting of the evaporator coils. At this point, the mechanism 01" the timer will throw or trip switch 46 from the full line position to the dotted line position, thereby completing the electric circuit through the solenoid valve 25 and open.- ing the latter to permit the hot gas to pass through pipe 20 to the evaporator coils and start the defrosting operation as previously de-: scribed. The defrosting will continue for the period predetermined by the setting 01 timer 42 and, when this period expires, the timer mechanism will throw switch 46 back to thefull line position, thereby closing solenoid valve 25 and restoring the apparatus to normal operation.

From the foregoing, it will be evident that the apparatus is wholly automatic in its control of the times at which the defrostings take place and that its automaticity conforms to the demands of operating conditions as distinguished from being controlled by an arbitrary setting. This results in assurance that defrostings will take place whenever needed and will not take place when not needed, thus combining eiliciency and effectiveness with ecenomy to a high degree.

In the modified form shown in Fig. 2 of the drawings everything is the same as shown and described in connection with Fig. 1, except that pressure switch 3| is omitted, and power wire 29 runs directly to one terminal of thermostatic switch 35. Hence, in this form of the invention the on and off cycles of the apparatus, i. e. when the compressor is in and out of operation, are controlled by the temperature within the refrigcrating chamber only; but the operations of the timer 42 and the parts it controls remain the same as has been described.

In the modified form of the invention shown in Fig. 3, the construction and operation are the same as described in connection with Fig. 1, except that thermostatic switch 35 is omitted and wire 31 makes direct connection from motor 3 to terminal 30 of pressure switch 3|. In this case,

\ cuit from the source of fan motor 39, and hence fan 40, is attained. In this modified form of Fig. 4, the wire 29 from the source of current supply runs directly to pivot terminal 45 of switch 46 and. through the said switch, to one brush of fan motor 39, which is here represented diagrammatically. The other power wire 28 runs directly to the other brush of fan motor 39. Pressure switch 3| is connected by a branch wire '56 withwire 29 and by another wire 51 with one terminal of motor 3; while the other terminal of motor 3 is connected by branch wire 58 to power wire 28. The terminals of timer 42 are connected by branch wires 59 and 66 with wires 5'! and 58 respectively.

As the result of this wiring it will be seen that operation of switch 3| will start or stop motor 3 and timer 42, but that it will have no effect upon fan motor 39 because switch 3| is not in the cirof power through motor 39.

The only times that fan motor 39 stops are when the mechanism of timer 42 throws switch 46 from the full line position to the dotted line position to open solenoid valve 25 and start defrosting. This movement of switch-46 stops fan motor 39 because there is no occasion for fan 40 to be running while defrosting is taking place. The pressure switch 3| shown in this modified form of the invention could be substituted by the thermostatic switch 35 or any other suitable unit of this character.

The valves 26 and 21 shown in Fig. 1' of the drawings may be manually operated as indicated by the hand wheels thereon, but the thermostatic expansion valve I4 is automatically controlled, in a well known manner, by a suitable device such as a feeler bulb 6| that is attached to pipe l8 and connected to valve l4 by a capillary tube 62. The usual louvers 63 are pivotally mounted in the evaporator housing 23 and may be adjusted for control of the direction of the air current from fan 40. A drip pan 64 is located below evaporator l6, II, to receive water resulting from the melting of ice during defrosting periods,,which water is carried to a sewer, or other disposal outlet, by pipe 65. Finally, a small pipe 66 connects the bottom of tank I 9 with the oil sump 2 of compressor in order to drain on from tank |8 such the on and oil cycles of .the apparatus are con- 1 trolled by the pressure within suction pipe 5, 8, only, but the operations of the timer 42 and the parts it controls are again the same as has been described.

In the forms of the invention already described, the fan motor 39 is cut out or stopped whenever motor 3 is cut out or stopped, because switches 3| and 35 are in the power line which leads to motor 39 as well as to motor 3. In some, if not many, instancesit is desirable that the fan 40 continue in operation though the compressor be stopped. This is especially desirable when the refrigerating chamber is crowded because the continued operation of the fan will maintain a circulation that tends to the establishment of uniform temperature throughout all portions of the chamber, and also tends to better control of the on and oil. cycles of the apparatus by providing against subjecting the feeler bulb of the thermostatic valve to temperatures that are not truly reflective of the effective temperature in the chamber.

Fig. 4 of the drawings shows a modified form of L the apparatus in which this continuous operation oil as may be deposited therein from the circulating fluid.

With reference to all the forms shown, it may be noted that the apparatus of this invention operates upon the principle of automatically totalling the number of operating hours and/or minutes of the compressor, making the said total an average measure of the mulate upon thetherefrom the need evaporator unit, determining for defrosting, and automatically initiating the same; thus timing the successive defrostings on the basis of compressor operation rather than upon a predetermined fixed interval.

I desire it to be understood that various changes may be resorted to in the form, construction, material and arrangement of the several parts, without departing from the spirit and scope of my invention; and hence I do not intend to be limited to details herein shown or described except as they may be included in the claims or required by disclosures of the prior art.

What I claim is: k p

1. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrosting the evaporator, means for registering the operation of the compressor, and means controlled by amount of ice accutermined time;

prising, a compressor, an

11 the operation of the registering means for activating the defrosting means when the compressor has been operating for a predetermined time.

'2. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrosting the evaporator, means for registering the oper-.

ation of the compressor, and means controlled by the operation of the registering means for activating the defrosting means when the compressor has been operating for a predetermined time and for deactivating the defrosting means when the latter has been operating for a predetermined time.

3. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrosting the evaporator, a timing device for registering the operation of the compressor, and means controlled by the operation of the timing device for activating the defrosting means when the compressor has been operating for a predetermined time.

4. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrosting the evaporator, an electrical timing device for registering the operation of the compressor, and

' operation of the means controlled by the operation of the timin device for activating the defrosting means when the compressor has been operating for a predethe character described comevaporator, means for .operating the compressor, means for defrosting the evaporatona timing device for registering the operation of the compressor, and means controlled by the operation of the timing device for 5. Apparatus of activating and deactivating the defrosting means I when the compressor predetermined time. I

6. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrostin the evaporator, an electrical timing device for registering the operation of the compressor, and means controlled by the operation of the timing device for activating and deactivating the defrosting means when the compressor has been operating for a predetermined time. 7. Apparatus of the character described comprising, a compressor, an evaporator, electric means for operating the compressor,.means for defrosting the evaporator, an electrical timing device for registering theoperatlon of the compressor, a thermostatic switch for governing said has been operating for a electric means and said, timing device, and means regulated by the timing device for activating the defrosting means when the compressor operating means has been active for a predetermined time.

8. Apparatus of the character described comprising, a compressor, 'an evaporator, electric means for operating the compressor, means for defrosting the evaporator, an electrical timing device for registering the operation of the compressor, a pressure switch for governing said electric means and said timing device, and means regulated by the timing device for activating the defrosting means when the compressor operating means has been active for a predetermined time.

9. Apparatus of the character described comprising, a compressor, an evaporator, electric means for operating the compressor, means for defrosting the evaporator, an electrical timing device for registering the operation of the compressor, thermostatic and pressure switches for governing said electric means and said timing device, and means regulated by the timing device for activating the defrosting means when the compressor operating means has been active for a predetermined time.

10. Apparatus of the character described comprising, a compressor, an evaporator, means for operating the compressor, means for defrosting the evaporator, a fan associated with the evaporator, means for automatically starting and stopping the compressor operating means. means for activating the defrosting means when the compressor operating means has been active for a predetermined time, means for operating the fan when the compressor operating means is both active and inactive, and means for stopping the fan operating means when the defrosting means is activated.

11. Apparatus of the character described comprising, a compressor, an evaporator, means for intermittently operating the compressor, means for defrosting the evaporator, a device for totaling the duration of the intermittent periods of compressor.- and means controlled by the operation of the said device for activating the defrosting means when the total of compressor operation equals a predetermined time.

12. Apparatus prising, a'compressor, an intermittently operating the compressor, means for defrosting the evaporator, a device for totaling the duration of the intermittent periods of operation of the compressor, and means conof the character described comevaporator, means for activating and deactivating the defrosting means when the total of compressor operation equals a 40 predetermined time.

13. Apparatus of the character described comprising, a compressor, an evaporator, means for intermittently operating the compressor, means for defrosting the evaporator, an electrical timing device for totaling the duration of the intermittent periods of operation of the compressor,; and means controlled by the operation of the said device for activating the defrosting means when the total of compressor operation equals a predetermined time.

14. Apparatus of the character described comprising, a compressor, an evaporator, means for intermittently operating the compressor, means for defrosting the evaporator, an electrical timing device for totaling the duration of the intermittent periods of operation of the compressor, and means controlled by the operation of the said device for activating and deactivating the defrosting means when, the total of compressor operation equals a'predetermined time.

" GEORGE FRIE.

REFERENCES CITED The following references are of record in the file of this patent:

7 UNITED STA ES PATENTS 2,351,140 McCioy June 13, 1944