US2251503A

US2251503A - Refrigeration control system

Info

Publication number: US2251503A
Application number: US232574A
Authority: US
Inventors: Charles B Spangenberg
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1938-09-30
Filing date: 1938-09-30
Publication date: 1941-08-05
Anticipated expiration: 1958-08-05

Description

Aug. 5, 1941. c.' B. SPANGENBERG 2,251,503 REFRIGERATION CONTROL SYSTEM y Filed sept. so, 1938 i '2 sheets-sheet 1 so 28 l Aug. 5, -1941.

c. B. SPANGENBERG 2,251,503 REFRIGERATION CONTROL SYSTEM Filed Sept. 30, 1938 2 Sheets-Sheet 2 Patented Aug. 5, 1941 UNITED STATES.` PATENT OFFICE REFRIGERATION CONTROL SYSTEM Charles B. Spangenberg, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application September 30, 1938, Serial No. 232,574

, ze claims. `(cl. 62-4) This invention relates to refrigeration control systems and to improvements in the component parts thereof.

The primary object of this invention is to provide an improved control system for a refrigwherein the compressor may be stopped when either the pressure on the low pressure side of the evaporator decreases to a predetermind low value or the pressure on the high pressure side of the rerigerating apparatus increases to a predetermined high value and wherein an automatic resetting overload cut out 1s provided to stop the compressor upon the occurrence of overload conditions. v.

Other objects and advantages will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings, in which:

Figure l a diagrammatic illustration of one form of the control system applied to a refrigerating apparatus, i

Figures 2 and `3 arepiiodified forms of a portion of Figure 1 for accomplishing substantially the same@ results asj'are accomplished in Figure Figure/f4 illustrates,'diagrammatically a modification of thecontrol system Iolf Figure 1 for accomplishing "a slightly different sequence of control, and u.

Figure 5 is a diagrammatic illustration of the manner of applying the overload cut-out mechanism to the controlv system of application Seerating apparatus having evaporator means for refrigerant flows from the receiver Il through a liquid line i8 into the evaporator yII and the evaporated refrigerant is withdrawn from the evaporator II through a low pressure or suction line I9 by the compressor I3. An expansion valve controls the supply of refrigerant to the evaporator II and it may be of the thermostatic type having a bulb 22 located at the discharge side of the evaporator and containing a volatile iluid and connected by a capillary tube 2| to the expansion valve. The construction thus far described is conventional in the art and therev fore a further description thereof is not considered necessary it being sufficient to state rial No. 101,107, filed September 16, 1,9436, by Wayland R. Miller.

Referringnow to Figure l the mediumto be Y conditioned or cooled by the refrigerating apparatus is shown to be air within an enclosure Il).

The medium in the enclosure I0 `is ycooled by a cooling coil preferably in theformof an evaporator I I. Refrigerant is supplied to and withdrawn f,

from the evaporator I I by means of a refrigeratlng apparatus generally designated at I2 whichl may comprise a compressor fl3 operated byan I electric motor I4. 'The compressor I31delivers compressed refrigerant throughahigh pressure line I5 into a condenser IG'and 'the condensed refrigerant is collected in a receiver il, `[liquid controller generally designated at 25 operating in response to changes in pressure on the high pressure side of the refrigerating apparatus and pressureon the low pressure side of the refrigerating apparatus, the latter being an indication or evaporator temperature. An overload cut-out mechanism generally designated at 2li-also controls the operation of the compressor motor to protect the same against4 overload conditions,A

The temperature responsive controller 24 may comprise a bellows 28 vcontaining a volatile fluid for operating a lever 29 'against the-action of anV adjustable tension spring 30. The lever 2!! in response to changes in temperaturel closes and opens a mercury switch 3l.v For purposes of .i1-

lustration it is assumed that when the tempera.- I. ture of the medium within the enclosure" llrises to 42 the mercury Switch 3l is tilted thev closed position and when the yterfnperature',,de-l` creases to 40 vthe mercury switchlll is tilte'd to the openposition@ The' controller 25 against the action of an adjustable tension spring 38.,y 'Qne-,eiidoithespring isfconnected tofthel lever-,551' andthe other end islconnect'ed a'nut f as srewftnreadedly'mont" dion; 'a Screwn. j By y `rotating tliegscrei'v 4 0', thgtension in ftheV spring' 38 ina'be adjuste'd'aiid hence the pressure set-gl ting of the bellows 34 may be adjusted. *The leverV mayv` corxl'prise` ajcsixl; 3'3.l in which is, mounted .abellows 34gco`nnected'by a', pipe 35 to the, low pressure `or suction line'.l9,"4 The bellows' operates a lever 36. pivoted', at 131,14

36 operates an arm 4| guided in a guide 42 and carrying at its upper extremity a screw 43. The screw 43 is adapted to engage a lever 44 pivoted at 45 and carrying a mercury switch 46, the mercury switch 46 being biased to the open position shown by its own weight. For purposes of illustration it is assumed that when the suction pressure rises to 35 lbs. the screw 43 tilts the mercury switch to a closed position and as soon as the pressure on the low pressure side of the refrigerating apparatus decreases a relatively small amount below this 35 lbs., the screw 43 disengages the lever 44 to allow the mercury switch 46 to open if it is not latched closed at this time.

The controller 25 also includes a bellows -48 mounted in the casing 33 and connected by a pipe 49 to the high pressure line |5. The bellows 48 operates a lever 50 pivoted at 5| against the action of an adjustable tension spring 52. One end of the spring 52 is connected to the lever 50 and the other end is connected to a nut 53 screw threadedly mounted on a screw 54. By rotating the screw 54 the tension of the spring 52 is adjusted and hence the pressure setting of the bellows 48 is adjusted. Lever 50 operates an arm 55 guided in a guide 56 and carrying at its upper extremity a screw 51. The screw 51 is adapted to engage a lever 58 pivoted at 59 for closing a mercury switch 60, the mercury switch 60 being biased to the open position shown by its own weight. For purposes of illustration it is assumed that when the pressure on the high pressure side of the refrigerating apparatus decreases to 140 lbs. the screw 51 tilts the mercury switch 60 to a closed position and when the pressure rises a relatively small amount above this 140 lb. value the screw |51 disengages the lever 58 to allow the mercury switch 60 to open providing it is not latched closed at this time.

A latch means generally designated at 6| is utilized for latching the mercury switch v46 closed during operation of the compressor after the mercury switch 46 has been closed in the manner pointed out above. This latch means may comprise a bell crank lever pivoted at 63 and having

arms

62 and 64. Mounted on the same pivot 63 with the bell crank lever is a latch member 65 provided with an abutment 66 :for engaging the arm 62 of the bell crank lever and also provided with an arm 61. 'I'he

arms

61 and 64 are provided with

lugs

69 and 10 connected together by a spring 60 for holding the abutment 06 in engagement with the arm 62.

A latch means generally designated at 1| is also provided for the mercury switch 69 for holding the same closed after it has once been closed in the manner pointed out above during the operation of the compressor. This -latch means 1| may comprise a bell crank lever pivoted at 13 and having

arms

12 and 14. A latch member 15 is pivoted on the pivot 13 and carries an abutment 16 for engaging the arm 12. The latch member 1.5 also carries an arm 11, the arms 11 and 14 being provided with

lugs

19 and 90, respectively, connected together by a tension spring 10 for holding the abutment 16 in engagement with the arm 12.

The latch means 6| and 1| are operated by an actuator 02 connected by a rod 03 to an armature 05, the rod 03 being guided in a guide 04. A core 96 and an operating coil 01 coact with the armature to raise the armature 05 and hence the actuator 02 when the operating coil 91 is energized.V Raising of the actuator 92 moves the latch means 6| and 1| outwardly to latch the

mercury switches

46 and 60 closed after they both have been closed in the manner pointed out above.

The arm 4| operated in response to changes in pressure on the low pressurev side of the evap orator carries a leg provided with a screw 9| for engaging the arm 61. For purposes of illustration it is assumed that when the pressure on the low pressure side of the refrigerating apparatus decreases to 10 lbs. the screw 9| will engage the arm 61 to overcome the spring 69 to release the latch member 65 from the lever 44 to allow opening of the mercury switch 46. In a similar'manner the arm 55 which is operated in response to changes in pressure on the high pressure side of the reirigerating apparatus is provided with a leg 92 carrying a screw 93 for engaging the arm 11 of the latch means 1.|. For purposes of illustration it is assumed that when the pressure on the high pressure side of the refrigerating apparatus increases to lbs. the screw 93 engages the arm 11 to move the same against the action of the spring 18 to disengage the latch member 15 from the lever 58 to allow opening movement of the mercury switch 60.

The overload cut-out mechanism generally designated at 26 may be provided with

control contacts

94 and 95 carried by a spring arm 96 mounted on the bracket 91 and a pivoted lever 98, respectively. Pivoted lever 98 is provided with a cam surface 99 which coacts with a bimetallic element |00 mounted on a bracket 0|. The bimetallic element |00 is heated by a heater |02 located in the energizing circuit for the compressor motor I4. Upon the occurrence of an overload condition in the compressor motor I4 the current flow through the heater element |02 becomes excessive which warps the bimetallic element 00 to the leit and when the bimetallic element |00 has moved suillciently to the left the lever 98 moves downwardly to separate the

contacts

94 and 95 to interrupt the energizing circuit for the compressor motor. The bimetallic element |00 carriesa contact |04 in an insulated manner which engages a contact |05 carried by an arm |06 mounted on a bracket |01 when the bimetallic element |00 tlexes suillciently far to the left to allow separation of the

contacts

94 and 95. Engagement of the contacts |04 and |06 energizes an auxiliary heater |00 for ilexing upwardly a bimetallic element |09 mounted on a bracket ||0. Upward movement of the bimetallic element |09 engages a lug on the lever 90 to reclose the

contacts

94 and 95. The heater |90 is so selected that a relatively long time interval is caused to elapse before the-

contacts

94 and 95 are reclosed and at this time the bimetallic element |00 has cooled sumciently to again latch the

contacts

94 and 95 closed. Accordingly the overload cut-out mechanism 99 opens the energizing circuit for the compressor motor |4 upon the occurrence ot an excessive current ow in the heater element |02 and automatically recloses the energizing circuit for the compressor motor after the lapse of a predetermined timed interval.

Power is supplied to the compressor motor |4 and to the control system in general by means of line wires ||2 and ||3 leading from some source of power (not shown).

For purposes of illustration it is assumed that the temperature of the medium within the enclosure 0 increases to 42 to close the mercury switch 3|, that the pressure on the low pressure side of the refrigerating apparatus increases to through wire ||4, heater |02, wire IIE, lever 88..

contacts

95 and 94,arm 86, wire ||6, compressor motor |4, wire ||1, mercury switch 3|, wire ||8, mercury switch 60, wire H8, operating coil 61, wire |20, mercury switch 46, and wire |2| back to the other line wire ||3.A Completion of this circuit energizes the compressor motor |4 and hence places the refrigerating apparatus in operation and also energizes the operating coil. 81 for raising the actuator 82 to-latch the mercury switches 46 and 60 closed. 'I'he compressor motor |4 and hence the refrigerating apparatus remains in operation even though the pressure onV the low pressure side of the refrigerating apparatus decreases below 35 lbs. and the pressure on the high pressure side of the refrigerating apparatus increases above 140 lbs. until such time as the temperature within the enclosure Iv decreases to 40. When the temperaturel within the enclosure |0 decreases to 40 the mercury switch 3| is tilted to the 0H position to break the energizing circuit to the compressor motor |4 and to deenergize the operating coil 81. The latch means 6| and 1| are thereupon released and the mercury switches 46 and 60 are tilted to the off positions as shown. I'he rei'rigerating apparatus can again be placed in operation only when the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. and the pressure on the high pressure side of the refrigerating apparatus decreases to 140 lbs.

If during the operation of the refrigerating apparatus the pressure on the low pressure side of the refrigerating apparatus decreases to 10 lbs. before the temperature in the enclosure 10 de- Greases to 40 the screw 9| releases the latch means 6| to allow the mercury switch 46 to open. Opening of the mercury switch 46 breaks the energizing circuit for the compressor motor |4 and deenergizes the operating coil 81 whereby both latch means 6| and 1| are' returned to the positions shown in Figure 1 to open the mercury switches 46 and 60. Here again the refrigerating apparatus lcan again be placed in operation only when the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. and the pressure on the high pressureV side oki; the refrigerating apparatus decreases to V140 l s.

If the pressure on the high pressure side of the refrigerating -apparatus should increase to 180 lbs.`before the temperature within the enclosure l0 decreases to 40 the screw 83v releases the latch means 1| to allow the mercury switch 60 to open. Opening of the mercury switch 60 breaks the energizing circuit for the compressor Amotor |4 and deenergizesthev operating coll 81 to release -both latch means 6| and. 1| to allow opening of the mercury switches 46 and 60. After this has occurred the refrigerating apparatus may again be placed in operation only when the pressure on the low pressure side of the refrigerating apparatus increases; to 35 lbs. and the pressure on the high pressure side` of the refrigerating apparatus decreases to 140 lbs.

If during the operation of the refrigerating apparatus the current flow in the energizing circuit for the compressor motor |4 should become excessive the

control contacts

94 and 95 of the overload cut-out mechanism 26 will separate to break the energizingvcircuit for the compressor lmotor I4 and deenergize the operating coil 81 to release the latch means 6| and 1| and open the mercury.

switches 46 and 60. Accordingly following an overload condition the refrigerating apparatus can not againl be placed in operation until the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. and the pressure on the high pressure side of the refrigerating apparatus decreases to lbs. As

pointed out above the overload cut-out mechavnism 26 is automatically reclosed following the lapse of a predetermined timed interval so that when the overload condition no longer exists the refrigerating apparatus may be automatically restarted to maintain desired temperature conditions within the enclosure |0.- Since it is impossible to start the refrigerating apparatus until the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value, illustratively 140 lbs., starting of the compressor against relatively high head pressures is prevented and therefore the main cause for overload conditions is eliminated in this system. Likewise the refrigeratlng apparatus is shut down when the pressure on the high pressure side of the refrigerating vapparatus increases to a, predetermined high value, say lbs., or the pressure on the low pressure side of the` refrigerating apparatus decreases to a low value of, say 10 lbs. Accordingly in such a system it is perfectly satisfactory to utilize an automatic resettable overload cut-out mechanism since the majority of causes of overload conditions are eliminated by the control system. About the only condition which will cause the overload cut-out mechanism to trip open is a low voltage condition which is not permanent in nature or extremely detrimental to the operation of compressor motor |4. From the above it is seen that the use of an automatically resettable (overload cut-out mechanism in this type of control system is extremely beneficial. Since it is impossible to start the compressor until the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs., which may be a value corresponding to the defrosting temperature of the evaporator Il, defrosting of the evaporator 4|| during each cycle of operation is assured.

Other means may be utilized for causing the latch means 6| and 1| to hold the

switches

46 and 60 closed during operation of the refrigerating apparatus and two of these means are shown in Figures 2 and 3.

In Figure 2 'a combined ball governor and Bowden wire arrangement generally designated at |30 is utilized for this purpose. A collar |3| is rigidly secured to the compressor motor shaft or compressor shaft |32 for rotation therewith. Spring straps |33 carrying weights |34 are connected to the collar |3| and to a collar |35 slidably mounted on the shaft |32. Upon rotation of the compressor motor or compressor shaft |32 the weights |34 fly outwardly tofmove the collar |35 towards the left. The collar |35 is provided with a groove |36 for receiving a pin |31 carried by a yoke |38. Secured to the yoke |38 is a wire |38 cury switches 46 and 60 closed during the operation of the refrigerating apparatus. The combined ball governor and Bowdenwire arrangement therefore provides exactly the same operation as the electromagnetic actuator of Figure 1 and therefore a further description is not considered necessary.

In Figure 3 the actuator 82' is operated by a iuid pump arrangement generally designated at E44. The actuator 82 is connected by a rod |45 to a diaphragm |46 which is clamped to a pressure chamber |41 by a ring |48. A uid line |49 c onnects the pressure chamber under the diaphragm |46 to the discharge side of a gear pump |50 which is operated by the compressor motor shaft or the compressor shaft. Fluid is supplied to the gear pump |50 by a supply line |5| leading from a sump |42. Accordingly when the compressor is placed in operation the gear -pump forces the diaphragm |46 and hence the actuator 82 up- Y wardly to cause the latch means 6| and 1| to latch the mercury switches 46 and 60 closed during the operation of the refrigerating apparatus. When the refrigerating apparatus shuts down the uid in the pressure chamber leaks balclrthrough the gear .pump |50 to the sump|52 to allow the' to 35 1bs. a circuit is thereupon completed from Completion of this circuit causes operation of the compressor motor I4 and energization of the oppressure on the high pressure side of the refrigv erating apparatus decreases to 142 lbs. the mercury switch 60 and the latch means 1| may be omitted as is illustrated in Figure 4. In Figure 4 the bellows 48 which'is operated in accordance with changes in pressure on the high pressure side of the refrigerating apparatus operates aA lever pivoted at |56 against the action of an adjustable tension spring |51. One end of the tension spring |51 is'connected to the lever |55 and the other end is connected to a nut |58 screw threadedly mounted on a screw |59. By rotating the screw |59 the tension in the spring |51 may be adjusted and hence the pressure setting of the bellows 48 may be adjusted. Lever |55 carries a screw |60 which is adapted to engage the arm 61 of the latch means 6|, for example, when the pressure on the high pressure side of the refrigerating apparatus increases to 180 lbs.

Accordingly in the construction shown in Figure 4 the mercury switch 46 is closed when the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. and is heldclosed by the latch means 6| during operation of the compressor. If either the pressure on the low pressure side of the refrigerating apparatus de'- creases to 10 lbs. to cause the -screw 9| to engage the arm 61 or the pressure on the high pressure side of the refrigerating apparatus increases to 180 lbs. to cause the screw |60 to engage the arm 61 the latch means 6| is released to allow the mercury switch 46 to open.

Power is supplied to the compressor motor I4 in Figure 4 by line wires |62 and |61 leading from some source of power (not shown). Assume now that the temperature within the enclosure increases vto 42 to close the mercury erating,coi1 81 to latch the mercury switch 46 closed. The compressor motor |4 will thereupon remain in operation until either the temperature within the enclosure should decrease to 40 or the pressure on the low pressure side of the refrigerating apparatus should decrease to 10 lbs. or the pressure on the high pressure side of the refrigerating apparatus should increase to 180 lbs. or an overload condition should occur.

The overload cut-'out mechanism of this invention may also be applied to the control system shownand described in application Serial No. 101,107, led Sept. 16, 1936, by W. R. Miller to accomplish substantially the same results as are accomplished in the control system of Figure 1.

'The application of the overhead cut-out mecha- I 'nism 26 to the control system of the W. R. Miller application is diagrammatically illustrated in Figure 5. The compressor motor I4 is here controlled by a relay or starter generally designated at |10 and comprising an operating coil |1| for operating switch arms |12 and |13 with respect to,contacts |14 and |15. When the operating coil |1| is energized the switch arms |12 and |13 are moved into engagement with their respective contacts |14 and |15 and when the operating coil |1| is deenergized the switch arms are moved out of engagement with their respective contacts by means of springs gravity or other means (not shown).

Contacts |16 and 11 are normally closedbut are open when the pressure on the high pressure side of the refrigerating apparatus increases to 180 lbs. and contacts |18 and |19 are normally open butare moved to a closed position when the pressure on the high pressure side of the refrigerating apparatus decreases to 140 lbs. Contacts and |8| are normally closed but are moved to an open position when the pressure on the low pressure side of the refrigerating apparatus decreases to 10 lbs. and contacts |82 and |83 are normally open but are moved to a closed position when the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. The mercury switch |84 is operated in accordance with variations in temperature being controlled and is moved to a closed position when the temperature increases to 42 and is moved to an open position when the temperature decreases to 40.

Control contacts

contacts

94 and 95, wire |90, contacts |18 and |11, wire 25 upon the occurrence of an excessive current flow through the heater |02 or the pressure on the 35 high pressure side of the refrlgerating apparatus increases to 180 lbs. or the temperature being controlled decreases to or the pressure on' the low pressure side of the refrigerating apparatus decreases to 1-0 lbs. When' any of these con- 40 tingencies occur the refrigerating apparatus can-lI not again be restarted until the mercury switch |84 is closed upon a call for cooling, the

control contacts

94 and 95 of the overload cut-out mechanism 26 are reclosed, the -pressure on the high 45 pressure side of the refrigerating apparatus decreases to 148 lbs. and the pressure on the low pressure side of the refrigerating apparatus increases to 35 lbs. Accordingly the sequence of operation is substantially the same as that of -50 the construction shown in Figure 1 although the construction of the two systems is entirely diierent. In Figure 5 the

control contacts

94 and 95 of theoverload cut-out mechanism are located in a pilot circuit while in Figure 1 they are shown 55 to be in the energizing circuit of the compressor motor.

Although for purposes of illustration several forms of this invention have been disclosed other forms thereof may become apparent to those skilled in the art upon reference to this disclosure and therefore this invention is to be limited only by the scope of the appended claims and prior art.

I claim as my invention:

1. In a control system for a refrgerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor, means responsive to a/condition which is a measure of evaporator temperature for closing the switch means whenvthe evaporator temperature rises to a predetermined high value foroperating the compressor, and latch means operated as an incident Completion of this circuitlmaintains the 30 to operation of thecompiessor for holding the switch means closed as long as the compressor remains in operation.

2. In a control system for a refrigerating apparatus including acompressor and evaporator means-for cooling a medium, the combination of, means including switch means for `controlling the operation of the compressor, means responsive to a condition which is a measure of evaporator temperature for closing the switch means when the levaporator temperature rises to a predetermined high value for operating the compressor,

latch means operated as an incident to operationV of the]y compressor for holding the switch means closed as long as the compressor remains in operation, and means operated by said condition responsive means when the evaporator temperature decreases to a predetermined low value forv releasing said latch means to open said switch means and stop operation of the compressor.

3. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means f or controlling the operation of the compressor, means responsive to the pressure on the high pressure side.oi

the refrigerating apparatus for closing the switch meansfwhen the pressure decreases to a predetermined low value for Operating the compressor, and latch means operated as an incident to Voperation of the compressor for holding the switch means closed as long as the compressor/ remains in operation.

4. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor,.v means responsive to the pressure on the high 'pressure side of the reirigerating apparatus for closing the switch means when ythe pressure decreases to a. predetermined low value for operating the compressor, latch means operated as an incident to operation of the compressor for holding the switch means closed as long as the compressor remains in operation, and means operated by said pressure responsive means when the pressure increases to a predetermined high value for releasing said 4|latch means to open said switch means and stop operation of the compressor.

5. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor, control means responsive to a condition which is a measure of evaporator temperature, means controlled'by said control means for closing said switch means when the evaporator temperature rises to a predetermined high value for operating the compressor, latch means operated as an incident to operation of the compressor for holding the switch nieans closed as long as the compressor'remains in operation, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, and means controlled by said last mentioned control means for releasing said latch means when the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value to open said switch means andv stop operation of the compressor.

6. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor, control means responsive to .a condition which is a measure of evaporator temperature, means controlled by switch means closed as long as the compressorV remains in operation, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, and means controlled by both of said control means for releasing said' latch means when either the evaporator temperature decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value to open said switch means and stop operation of the compressor.

'7. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor, control means responsive to a condition which is a measure of evaporator temperature, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, means controlled by said control means for closing said switch means when both the evaporatortemperature increases to a predetermined high value and the pressure on the vhigh pressure side of the refrigerating apparatus decreases to a predetermined low value,

' and latch means operated as an incident to operation of the compressor for holding the switch means closed as long as the compressor remains in operation.

8. 'In a control system for a. refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including switch means for controlling the operation of the compressor, control means responsive to a condition which is a measure of evaporator temperature, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, means controlled by said control means for closing said switch means when both the evaporator temperature increases to a predetermined high value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value, latch means operated as an incident to operation of the compressor for holding the switch means closed as long as the compressor remains in operation, and means controlled by said control means for releasing said latch means when either the evaporator temperature4 decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value to open said switch means and stop operation of the compressor.

9. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including rst and second switch means arranged in series for controlling the operation of the compressor, first control means responsive to a condition which is a measure of evaporator temperature for closing the rst switch means when the evaporator temperature rises to a predetermined high value, second control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the second switch means when the pressure decreases to a predetermined low value, and latch means operated as an incident to operation of the compressor for holding the switch means closed as long as the compressor remains in operation.

10. In a control system for a refrigeratingapparatus including `a compressor and evaporator means for cooling a medium, the combination of, means including iirst and second switch means arranged in series for controlling the operation of the compressor, first control means responsive to a condition which is -a measure of evaporator temperature for closing the first switch means when the evaporator temperature rises to a predetermined high value, second control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the second switch means when the pressure decreases to a predetermined low value, latch means operated as an incident to operation of the compressor for holding the switch means closed as long as the compressor remains in operation, and means operated by both of said control means for releasing said latch means when either the evaporator temperature decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatusincreases to a predetermined high value.

1l. In a control system for aI refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including rst and second switch means arranged in series for controlling the operation of the compressor, iirst control means responsive to a condition which is a measure of evaporator temperature for closing the first switch means when the evaporator temperature rises to a predetermined high value, second control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the second switch means when the pressure decreases to a predetermined low value, and latch means for each switch means and operated as an incident to operation of the compressor for holding their .respective switch means closed as long as the compressor remains in operation.

l2. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including rst and second switch means arranged in series for controlling the operation of the compressor, rst control means responsive to .a` condition which is a measure of evaporator temperature for closing the iirst switch means when the evaporator temperature rises to a predetermined high value, second control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the second switch means when the pressure decreases to a predetermined low value, latch .means for each switch means and operated as an incident to operation of the compressor for holding their respective switch means closed as long as the compressor remains in operation, means operated by the first control means for releasing the latch means of the rst switch means when the evaporator temperature decreases to a predetermined low value to open the rst switch means, and means operated by the second control means for releasing the latch means of the second switch means when the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value to open the second switch means.

13. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the .combination of,

nrst switch means, first control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements by the medium for closing the first switch means upon a demand for cooling and for opening the first switch means when the cooling demand is satisfied, second switch means, secondvcontrol means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature rises to a predetermined high value, means controlled by the rst and second switch means for operating the compressor when both switch means are closed, and latch means operated as an incident to operation of the compressor for holding the second switch means closed as long as the compressor remains in operation.

14. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, first switch means, first control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium for closing the first switch means upon a demand for cooling and for opening the rst switch means when the cooling demand is satisfled, second switch means, second control means responsive to a condition which is a measure of vrises lto a' predetermined high value, means controlled by the first and second switch means for operating the compressor when, both switch means are closed, latch means operated as an incident to `operation of the compressor for holding the second switch means closed as long .as the compressor remains in operation, and means controlled by the second control means for releasing the latch means when the evaporator temperature decreases to a' predetermined low value to open the second switch means.

15. In a vcontrol system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, first switch means, first control means 'responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium for closing the first switch means upon a demand for cooling andffor opening the iirst switch means when the cooling demand is satisfied, second switch means, secon control means responsive to the pressure on the high pressure side of the refrigeratingapparatus for closing the second switch means when the pressure decreases to a predetermined low value, means controlled by the rst and second switch means for operating the compressor when both switch means are closed, latch means operated as an incident to operation of the compressor for holding the second switch means closed as long as the compressor remainsv in operation, and means controlled by the second control means for releasing the latch means when the pressure on the high pressure side of thevrefrlgerating apparatus increases to a predetermined high value to open the second switch means.

16. In a control system for a refrigerating ap-y paratus including a compressor and evaporator means for cooling a medium, the combination of, first switch means, rst control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium for closing the first switch means upon a demand for cooling'and for opening the first switchmeans when the cooling demand is satisfied, second switch means. second control means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature rises to a predetermined high value, means controlled by the first and second switch means for operating the compressor when both switch means areclosed, latch means operated as an incident to operationof the compressor for holding the second switch means closed as long as the compressor remains in operation, third control means responsive to the pressure on the high pressure side of the refrigerating apparatus for releasing the latch means when the pressure increases to a predetermined high value to open the second switch means.

17, In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of first switch means, first control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium for closing the first switch means upon a demand for. cooling and for openingthe first switch meansv when the cooling demand is satisfied, second switch means, second control means responsive to a condition which is a measure of evaporator :temperature for closing the second switch means when the evaporator temperature rises to a predetermined high value, means controlled by the first and second switch means for operating the compressor when both switch means are closed, latch means operated asan incident to operation of the compressor for holding the second switch means closed as long as the compressor remains in operation, means controlled by the second control means for releasing the latch means when the evaporator temperature decreases to a predetermined low value to open the second switch means, third control means responsive to the pressure on the high pressure side of the refrigerating apparatus for releasing the ylatch means when the pressure increases to a predetermined high value to open the second switch means.

18. In a control system for a refrigerating apparatus including a lcompressor and evaporator means for cooling a medium, the combination of,

` iirst switch means, iirst control means responsive to a condition of thev medium being cooled which is a measure of the cooling requirements of the medium for closing the rst switch means upon a demand for cooling and forropening the first switch means when the cooling demand is satisfied, second switch means, second control means responsive to a condition which is a measure lof evaporator temperature, third control means responsive to the pressure o the high pressure side of the refrigerating apparatus, means controlled by the second and third control means to close the second switch means when bothv the evaporator temperature increases to a predetermined high value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value, means evaporator temperature decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value to open the second switch means. I

19. In a control system for a refrigerating apparatus having an electrically operated compressor and evaporator means for cooling a medium, the combination of, an energizing circuit for the electrically operated compressor, means including control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the energizing circuit and operating the compressor only when the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value wherebystarting of the compressor against high head pressures is prevented, switch means for controlling the energizing circuit, means responsive to the current flow through the energizing circuit for tripping open the switch means for opening the energizing circuit in response to an excessive current ow, and means operative upon opening of the switch means for automatically reclosing the switch means after a time interval has elapsed.

20. In a control system for a refrigerating apparatus having an electrically operated compressor and evaporator means for cooling a medium, the combination of, an energizing circuitvfor the electrically operated compressor, control means responsive to the pressure on the low pressure side oi'` the refrigerating apparatus, control means responsive to the pressure on the high pressure side of the reirigeratng apparatus, means controlled by said control means to close the energizing circuit and operate the compressor only when the pressure on the low pressure side of the refrigerating apparatus increases to a predetermined high value and the pressure on the high pressure side of the reirigerating apparatus decreases to a predetermined low value and for maintaining the energizing circuit closed and the compressor in operation until either the pressure on the low pressure side of the refrigerating apparatus decreases to a predetermined low value or the pressure on the high pressure side of the reirigerating apparatus increases to a predetermined high value, overload cut-out means for controlling the energizing circuit including con-v trol means tripped open upon the occurrence of an excessive current ow through the energizing circuit for opening the energizing circuit, and means operative upon opening of the control means for automatically reclosing the control means following the lapse of a predetermined time interval.

21. 'In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, rst switch means, first control means responsive to the condition'of the medium being cooled for closing the rst switch means upon a demand for cooling and for opening the iirst switch means when the cooling demand is satisied, second switch means, second control means responsive to a condition which is a measure of evaporator temperature, third control means responsive to the pressure on the high pressure side of the refrigerating apparatus, means controlled by the second and third control means to close the second switch means when both the evaporator temperature increases to a predetermined high value and the pressure on the high pressure side of the reirig'erating apparatus decreases to a predetermined low value, means controlled by the iirst and second switch means for operating the compressor when both switch means are closed, latch means operated as an incident to operation of the compressor for holding the second switch means closed as long as the compressor remains in operation, means controlled by the second and third control means for releasing the latch means when either the evaporator temperature decreases to a predetermined low value or the pressure on the high pressure side increases to a predetermined high value to open the second switch means, overload cut-out means for the compressor including switch means for additionally controlling the operation of the compressor, means for latching the switch means closed, means responsive to a compressor overload condition for releasing the last mentioned latch means to cause the last mentioned switch means to open for stopping operation of the compressor, and means operative upon opening of the last mentioned switch means for automatically reclosing the switch means and latching the same closed following the lapse 'of a predetermined time interval.

22. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, means including control means responsive to a condition which is a measure of evaporator temperature for starting operation of the compressor only when the evaporator temperature rises to a predetermined high value and means operated directly and mechanically by the compressor for maintaining the compressor in operation.

23. Ina control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, lthe combination of,

iirst control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium, second control means responsive t0 a condition which is a measure of evaporator temperature, means controlled by both control means for starting operation of the compressor only when the iirst control means demands cooling and the evaporator temperature increases to a predetermined high value, and means operated directly and mechanically by the compressor for maintaining the compressor in operation until the first control means becomes satisiied.

24. In a control system for a reirigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, iirst switch means, iirst control means responsive to a condition yof the medium being cooled which is a measure of the cooling requirements of the medium for closing the first switch means upon a demand for cooling and for opening the rst switch means when the cooling demand is satistled, second switch means, second control means responsive to a condition which is a measure of evaporator temperature for closing the ,second switch means when the evaporator temparatus including a compressor and evaporator means for cooling a medium, the combination of, first control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium, second control means responsive to a condition which is a measure of evaporator temperature, means controlled by both control means for starting operation of the compressor only when the irst control means demands cooling yand the evaporator temperature increases to a predetermined high value and means actuated by operation of the compressor for maintaining the compressor in operation until the first control means becomes satisfied.

26. In a control system for a refrigerating apparatus including a compressor and evaporator means for cooling a medium, the combination of, first control means responsive to a condition of the medium being cooled which is a measure of the cooling requirements of the medium, second control means responsive to a condition which is a measure of evaporator temperature, means controlled by both control means for starting opera tion of the compressor only when the first control means demands cooling and the evaporator temperature increases to a predetermined high value and means actuated by operation of the compressor for maintaining said second control means in compressor operating position until the rst control means becomes satisfied.

CHARLES B. SPANGENBERG.-