US2277345A - Refrigeration control system - Google Patents

Description

March 24, 1942. A. B. NEWTON RFRIGERATION CONTROL SYSTEM Filed July 24, 1959 Sheets-*Sheet l l las SUCTION PRESSURE HEAD PRESSURE 'ro commsssan TQ LINE SUCTIQN PRESSURE March Z4, 1942. ,A. B. NEWTQN REFRIGERATION CONTROL SYSTEM Filed July 24, 1939 .Sheets-Sheet r2 ro yc'cmwnzrassen SUTION PRESSURE invento? .Alwin B. Newham A. B. NEWTON REFRIGERATION CONTROL SYSTEM Filed July 24, 1939 March 24., 1942.

3 Sheets-Sheet 3 Patented Mar. 24, `1942 UNITED STATES I 2,277,345 itErmGERA'rIoN CONTROL sYs'rEM Alwin B. Newton, Minneapolis, Minn., assignor to Minneapolis-Honeywell. Regulator Company, Minneapolis, Minn., a corporation of Delaware -v Application July 24,19

24 Claims.

I'his invention relates to a control system for Y a refrigerating apparatus having evaporator means for controlling the'conditlon of a medium and a mechanism for controlling the circulation of refrigerant through the evaporator-means. 6,'

An object of this `invention is to provide an automatic control system responsive to a condition which is a measure of evaporator temperature, such as suction pressure, and responsive to the condition of the medium being controlled by the evaporator means, such as space temperature,- for controlling' the mechanism to start circulation of refrigerant through the evaporator means only when the 'evaporator temperature increases to a predetermined high value, to continue circulation of refrigerant through the evaporator means when the condition of the medium is below a desired value-until the evaporator temperature decreases to. a predetermined value, or to continue circulation oi' re- 20 frigerant through the evaporator means as long as the condition of the medium is above the desired value even though the evaporator temperature should decrease below this predetermined Another object of this invention is to provide the above control system with a means responsive to the pressure on the high pressure side of the refrigerating apparatus for stopping circulation of refrigerant through theevaporator means if 30 the pressure should rise to a predetermined high value.` Provision may also be made for preventing starting of the refrigerating apparatus until the pressure on the high pressure side decreases to a predetermined low value and this 35 also forms another object of this invention.

Still another object of this invention is to stop operation of the refrigerating apparatus if the evaporator temperature or suction pressure should decreasey to a predetermined 10W value.

Further objects of this invention are directed to the construction and mode of operation of electrical and mechanical control arrangements for4 obtaining the above sequences of operation. I Other objects and advantages will becomelap- 45 parent to those skilled in the art upon reference to the accompanying speciiication, claims and drawings, in which:

ing -mechanically substantially that which is 55 accomplished electrically in Figures ,1' and 2 ;v

,A Figure 4 is a view similar to Figure 3` showing the parts in different positions; and

Figures/5 and 6 are diagrammatic illustrations 39, serial N o. 2363153 (ci. ca -4') in Figures 3 and 4.

Referring now to Figure 1 the refrigerating system is shown to be applied. to an enclosure I 0 for cooling the same. 'Ihe enclosure I0 may be a storage compartment, counter-case, water cooler, walk-in box, or other space which it is desired .to cool. The enclosure I0 is cooled by a cooling coil which may take the form of an evaporator II and refrigerant is circulated through the evaporator II by means of a re- 'frigerating apparatus generally designated atA I2. The refrigerating apparatus I2 may comprise a compressor I3 driven by an electric motor I4 lfordischarging compressed refrigerant through a high pressure line I 5 into a condenser I6. Condensed refrigerant is collected in a receiver I1 and is discharged through a liquid line I8- to the evaporator I I. Evaporated refrigerant is withdrawn from the evaporator II through a suction line I9 by the compressor I3.` The ilow vofrefrigerant to the evaporator II may be controlled by a thermostatic expansion valve having a thermal bulb 2l responding to the temperature of the refrigerant leaving the evaporator II. conventional in the art and therefore a further description thereof vis not considered necessary,

' it being sufcient to state that when the compressor I3 isA placed in operation the evaporator II performs a cooling function for cooling the enclosure I0. e

'I'he compressor motor I4 and hence the compressor I3 is controlled by a relay or starter gen` erally designated at 23 and this relay or starter is in turn controlled by a controller 24 responsive to a condition which is o, measure of 4evaporator i temperature such as suction pressure, by a con-` troller V25 responsive to the pressure-on the high pressure side of the refrigerating apparatus, and by a controller 26 responsive to a condition being perature within the enclosure I0.

The .relay or starter 23 may include-an operat-i ing coil 28 for operating switch arms 29 and30 withrespect tocontacts 3| and 32. When the operating coil 28 is energized theswitch arms 29 and 30 are moved into engagement with ,their respective contacts 3| and 32 and when the' operating coil 28 isdeenergized the switch arms are moved out of lengagement with their Vrespective contacts by means of springs, gravity or other means, not shown. 4 r

The ,controller 24 responsive .to a condition indicative oi' evaporator temperature such as suction pressure may comprise a bellowsl 34 con- I nested by a pipe 35'to the suction line I9. The` bellows 34 operates a lever 36 against the action of an adjustable tension spring 3l for operating of further modied forms of the invention G0 amercury switch 38.4 For purposes of illustration The above outlined construction is- II has deirosted. In this respect the switch- 38 might also be operated thermostatically by a bulb .responding to the evaporator temperature directly instead of being operated in accordance .with changes in suction pressure as illustrated l here.

The controller 25 responsive to the pressure on rthe high pressure side of the refrigerating apparatus may comprise a bellows 40 connected by a pipe 4I to the high pressure line I5. The bellows 40 operates a lever 42 against the action of an adjustable tension spring 43 for operating a mercury switch 44. For purposes of illustration it is assumedthat the mercury switch 44 is moved to an open position when the head pressure or pressures on the high pressure side of the refrigerating apparatus increases to 180 lbs. and is moved to a closed position when the head pressure decreases to 170 lbs.

The controller responsive to a condition controlled by the evaporator I I, such as the temperature within the enclosure l0, may comprise a beltemperature within the enclosure I increases to y 41 the mercury switch 5I is closed and when the temperature decreases to 40 the mercury switch 5| is open. While the controller 26 is shown for pllrDOses of illustration as responding to dry bulb A temperature within the enclosure III, the controller might also respond to the wet bulb temperature or the relative humidity within the en-` closure I 0 and still remain within the contemplaS tion of this invention.

Power is supplied to the control system and to the electric motor I4 for driving the compressor y I3 by means of line wires 230 and 23| leading from some source of power, not shown.

Assume now that the pressure on the high pressure side of the 'refrigerating apparatus is below 180 lbs. so that the mercury switch 4 4 is closed and that the temperature within the enclosure I0 is below 41 so that the mercury switch 5| is open. Also assume that the refrigerating apparatus is stopped and that the suction pressure is increasing. When the evaporator II has defrosted and the suction pressure has risen to 33 lbs., the mercury switch 38 is closed tocomplete a circuit fromithe line wire 230 through wire 232, mercury switch 38, wire 233, operating coil 28 and wire 234 back to the other line wire 23|. Completion of Ithis circuit energizes the operating coil 28 to move the switch arms 29 and 30 into ,engagement with their'respective contacts 3| and L32. Movement of they switch arm 30 into engagement with the contact 32 completes a load circuit for the compressor motor I4 which may be traced from the line wire 230 through wire 235, switch arm 30, contact 32, wire 236, compressor motor I4 and Wire 231 `back to the other line wire 23|. Hence, when the suction pressure increases t0 33 y, briefly as follows.

vis cyclically operated by the suction pressure im. the compres-sor ls is started to circulate re- 'frigerant'through the evaporator I I and the com- Assume now that the temperature within the enclosure I 0 rises to 41 to close the mercury switch 5I, However no circuits are completed immediately upon closure of the mercury switch 5| since the circuit through the mercury switch 5| also passes through the switch arm 29 and contact 3| ofthe relay or starter 23; When the suction pressure increases to 33 lbs. to start the compressor I3 in the manner pointed out above the switch arm 29 of the relay or starter 23 engages the contact 3| and if at this time the mercury switch 5| of the temperature responsive controller 26 is calling for operation of the compressor, a circuit is then completed from the line wire 230 through wire 232, wire 240, mercury switch 44, wire 24|, mercury switch 5|, wire 242, contact 3| switch arm`29, wire 243, operating coil 28 and wire 234 back to the other line wire 23|. Completion of this circuit maintains the relay or-starter 23 pulled in and hence the compressor I3 in operation until such time as the temperature within the enclosure I0 decreases to 40 to open the mercury switch 5I regardless of whether the suction pressure decreases below 27 lbs. Thus after the compressor is placed in operation by the suction pressure controller 24 it will remain in operation until such time as the temperature within the enclosure I0 decreases to 40 to open the mercury switch 5| of the temperature responsive controller 26. Desired temperature conditions are therefore at all times maintained within the'` enclosure I0.

It is here noted that the controller 25 responsive to the pressure on the high pressure side of the refrigerating apparatus is located in series with the temperature responsive controller 26 so that if the pressure on the high pressure side of the refrigerating apparatus should become excessive, as illustrated over lbs., then the last mentioned circuit is interrupted and the relay or starter 23 is dropped out to stop operation of the compressor I3. The compressor I3 cannot again be restarted until such time as the suction pressure increases to 33 lbs. to close the mercury switch 38.

The operation of Figure 1 may be summarized The refrigerating apparatus controller 24 and the compressor cannot be started until such time as the suction pressure increases to a value indicating. that the evaporator has defrosted. If when the compressor .is started by the suction pressure controller 24 in operation it is impossible therefore to start contact member 89 carried by a terminal 90.to

the refrigerating apparatus until such time as the evaporatorjl has defrosted. .If during the operation of the compressor the pressure on the high. pressure side of the refrigerating apparatus should become excessive then the refrigerating 1 5 apparatus is stopped and cannot again be 're started until the evaporator Ili has defrosted.

Figure 2 illustrates adierent arrangement for accomplishing substantially the same results as areaccomplished in Figure 1. In Figure 2 10 the compressor motor and hence the compressor are controlledby a unitary control arrangement generally designated at 55 which may be' of the type shown .and described in application Serial No. 196,447 led by Albert L. Judson and Carl G. Kronmiller on March 17, 1938.- For purposes of illustration in this application the unitary conl trol arrangement55 is shown to include a conf trol device 56 responsive to a condition which is a measure of evaporator temperature such as suction pressure, a control-device 51 responsive to head pressure, that is Athe pressure on the' high pressure side of therei'rigerating apparatus, an overload cut-out 58 and a relay or starter 59. 'I'he compressor motor'and hence the com- 25 pressor are also controlled by a controller 60 responsive to a condition controlled by the evaporator such as compartment temperature and if desired by a second controller 6I responsive to a condition which is a measure. of evapd 30 rator temperature such as suction pressure.

The control device 56 of the unitary control arrangement 55 responsive to changes in suction ried lby the bridge member 10 is adapted to en;

refrigerating apparatus.

gage a contact member 12 carried by a terminal 45 13. A second contact 14 carried by the bridge Y.

^ member 10 is adapted to engage a contact member 15 carried by-a terminal 16. A pair of concentrically arranged cams'11 and 18 are utilized |08 connected by a wire separate the contact member 89 from a contactor 9|. The abutment surface 86 is adapted to engage a contact member 92 carried by the terminal 16 to move the contact member 92l out of engagementwith a contact 93. For purposes ofillustration it is assumed that upon an in-l crease' in pressure on theA high pressure side of the refrigerating apparatus the contact member 92 ls flrst moved out of engagement with the contact 93-at ,140 lbs. and then the contact member 89 is moved out of engagement with the contact 9| at 180 lbs.. Conversely upon a decrease.

in head pressure the contact member 89 4iirst engages the contact 9| at 180 lbs. and then the contact member 92 engages the contact 93 at 140 lbs.

`The overload cut-out device may comprise a housing 94 to which is secured a terminal 95 and-a contmt 96.. Aheater element 91 is connected across the terminal 95 and the contact 96 for heating a thermostatic element enclosed within the housing 94. When the current liow through the heater-element-91 becomes excessive the thermostatic element.. not'shown, trips a latch to separate control contacts 98 and 99. y The control contacts 98 and 99 may be manually reclosed b y a manual reset lever I 00.

' The relay or starter 59 may comprise an oper-V ating coil |02 for operating bridge members |08 and |06. When the operating coil |02 is energized the bridge member |03 ismoved into en respective contacts by means of springs, gravity` or other means, not'shown. The unitary control arrangement also includesa controlterminal 41- to the .contact |04 and a load terminal |09.

The controller responsive to the condition' being controlled by the evaporator, such as enclosure temperature, may comprise a bellows connected by a capillary tube H2 to a bulb H3 f .l

for independently adjusting the position of the..50 contracted inaccordance with changes in temcontact members 12 and 15 with respect to their contacts 1| and 14.- For purposes of illustration it is assumed` that the parts yare so arranged that upon an increase in suction pressure`the` perature. 'Ihe bellows I|| operates a lever ||4 against the action of an adjustable tensionspring H5 for operating a mercury switch |I6.'.1"or4 purposes of illustration iti'svassumed that when contact 1| rst engages the contact member.-v 12 l55 the temperature atl'ecting the bulb I3 increases at 27 lbs. and then the contact 14 engages the contactmember I5y at 33 lbs. Conversely upon a decrease in suction pressure. the contact 14 rst disengages the contact member I15 at 33 lbs.v and then the contact 1| disengages the contact ber 12 at 27-lbs. y

The control device 51 of the unitary control arrangement 55 responsive to changes i headV pressure may comprise a bellows 80 co ected by apipe"8| to the high pressure line of the 65 The, bellows 80 operates a lever 82 fulcrumed on a fulcrum mem.

aber 88 against the action of an adjustable ten-l sion spring 84.l Onej end of the tensionspring r when-the suction pressure rises to 18 lbs. the

84 is connected tothe lever 82 an'd the-other 7d I end is connected to an adjusting screw arrange- \to 41 the mercury switch ||6 is closed and when the temperature decreases to 40 the mercury switch H6 is opened. l The controller 6| responsive to a condition inmemmsdicative of evaporator temperature such as suc- 'tion-pressure may comprise =a bellowsl ||8 con- 'nected by a pipe ||9 tothe suction line of the 're'frigerating apparatus. The ,bellows H8 operates a lever |20 against the .action of an ad- -justabletension spring |2|to operatea mercuryswitch |22. For purposes of illustration' it is .as-

."sumed that when .the'suction pressuredecreases to 15 ibs. the mercury switch m is lopened and mercury switch |22 is rec1osed.. However, as far as the sequence of operationis concerned the mercury switch |22 may be reolosed at any suctrol arrangement 55 engages the contact memand |22 leading from some source of power, not

cury switch |22 opens when the suction pressure decreases to lbs. and is reclosed by the time the suction pressure rises to 33 lbs.

A manual switch generally designated at |23 5 'may comprise a switch arm m adapted to engage contacts |25'and |22. If it be desired to connect the suction pressure controller 2| into .the control circuit the switch arm |24 is moved |24 is moved into engagement with the contact 22. If it be desired to eliminate the temperature control'feature from the system, then the manual switch |24 may be positioned as shown in Figure 2. 4

Power is supplied to the-control system and to the compressor motor by means of lineA wires |22 shown.

Assume now that the temperature within the enclosure is below 41 so that the mercury switch |,|2 of the temperature responsive controller 50 is opened, that the switch arm |24 of the manua1 switch |23 is engaging the contact |25 so that f the suction pressure responsive controller 2| is included in the system, that the suction pressure increases to 33 lbs. to cause the contacts 1| and 14 to engage the contact members 12 and 15 30 and thatrthe head pressure decreases to '140 lbs. L to cause the contact membersll, and 22 to engage the contacts 2| and 23. Underthese conditions a starting circuit for the relay or. starter 52 is completed and this starting circuit-may be traced from the line wire '|22 through contact 2|, contact member, terminal 20, conductor |32, terminal 13, contact member`12, contact 1|, bridge member 12, contact 14, contact members 12 and 22, contact 23, conductor |3I, contact |05, conductor |32, control contacts 23 and 22, conductor |33, operating coil |22, conductor |34 and terminal |22 back to theother line wire |29. Completion of this circuit energizes the operating coil |22 to move the bridge'members |03 and |22 into engagement with their respective-contacts.

Movement of the bridge member |22 into ensagement with the contacts and |21 completes a load circuit which may be traced from the line wire |22 through contact 2|, wire |32, terminal 22, heater element 21, contact 22, bridge member |22, contact |21, wire*|31, the compressor motor, wire |32, and terminal |22 back to the other line wire |22. 'Thus when the suction pressure increases to 33 lbs. the compressor motor and hence the compressor is placed in operation.

Movement of the bridge member |23 into engag'ement with the contacts |04 and |25 completes a iirst maintaining circuit for the operating coil 52 which may be traced from the line wire |22 through contact 2|, contact member 22. terminal 22, conductor |32, terminal 13, contact member 12, contact 1|, bridge member 12, conductor |42, contact |24, bridge member |03, contact |25, conductor. |32, control contacts 22 and 22, conductor |33, operating coil |22, conductor |34, and terminal |22 back to the other lin'e wire |22. Completion of this circuit maintains theA compressor motor and hence the refrigerating apparatus in operation until either the `suction pressure decreases to 27 lbs. to move the contact member 12, out of engagement with the contact 1| or until the pressure on the high pressure side of the reirigerating apparatus increases to -l 75 r f 2,271, yser 1s. A11 that is necessary is that the merlbs. to move the contact member 22 out of engagement with the contact 2|. Accordingly when both the suction pressure increases to a predetermined high value, illustratively 33 lbs., and the pressure on the highpressure side de,- creases to a predetermined low value, illustratively lbs., the compressor of the refrigerating apparatus is started and the compressor remains in operatiomuntil either the suction pressure decreases to an intermediate value of illus-v tratively 27 lbs.,4 or the head pressure increases to a high value of lbs.

Assume now that the' temperature within the enclosure increases to 41'to close the mercury switch ||6 of the temperature responsive con--A troller 60. Here as in the modication of Figure 1 this alone cannot start operation of the compressor. Under these conditions when the suction pressure increases to 33 lbs. and the head pressure decreases to 140 lbs. to pull inthe relay or starter 59, a second maintaining circuit is completed from the line wire |23, through contact Slfeontact member 29, terminal 90, conduc'- tor |30, terminal 13, wire |42, mercury switch H2, wire |43, switch arm |24, contact |25, wire \|44,` mercury switch |22, wire |45, contact |26, wire |46, terminal |02, conductor |41, contact |04, bridge member |03, contact |05, conductor |32, control contacts 92 and 99, conductor |33. operating coil |02, conductor |34, and terminal |09 back to the other line wire |29. Completion of this circuit maintains the relay or starter 59 pulled in and hence the compressor in operation until either the temperature within the compartment decreases to 40 to openthe mercury switch` IIB or the pressure on the high pressure side of the refrigerant apparatus increases to 180 lbs.

to move the contact members! out of engagement'with the contact 9|. It is also noted that the mercury switch |22 of the suction pressure responsive controller 2| `islincluded in series in this second maintaining circuit Vso that if the suction pressure decreases to 15 lbs. to openthe mercury switch |22 the relay or starter 59 is also dropped out to stop operation of the compressor. After the compressor has been lstopped by the' occurrence of either of these three conditions it cannot again be restartedA until such time as theA suction pressure increases to 33 lbs. and thehead pressure decreases to 140 lbs.

The operation of Figure 2 may be summarized briefly as follows. When the temperature vre-I sponsive controller 221s satisfied the compressor .is started when the suction pressure rises to a predetermined value, illustratively 33, lbs., andY g the head pressure decreases to a ,predetermined value, illustratively 140` lb's., and is maintained in. operation untileither the suction pressure. de-

creases to an intermediate value, illustratively 27 lbs.. or the head pressure increases to a high value, illustratively 180 lbs. In this way the compressor is intermittently operated in accord# j ance with changes in suction pressure or evaporator temperature. l. IL when the compressor is started as outlined above the-temperature within Q the compartment rises to a predetermined value,

illustratiyely 41, the compressor is maintained in operation until either the temperature within the compartment decreasesto a' redetermined value, illustratively 40, or the suction pressurel l,decreases to a predetermined low value, illustratively 15 lbs., or until the/head pressure increases to a predetermined high value; illustratively 180 lbs. In this Way desired temperatureconditions ,are at all times lrx'iaintained within the enclosure.

wise direction about the pivotv |81 by means of e Referring now to Figures 3 and 4, there is disclosed a mechanical arrangement for accomplishing substantially the same results as are accomplished by the electrical arrangement of Figure l2. Here a single control arrangement is generally designated at |50 and is provided with a control device|5| responsive to a condition which is a measure of evaporator temperature such as suction pressure, a control device |52 responsive to head pressure or pressure on the high pressure side of the refrigeratifng apparatus, and a control device |53 responsive to a condition controlled by the evaporator such as the temperature of the enclosure for operating a switching mechanism generally designated at |54.' n

The control device |5| responsive to a condition which is a measure of evaporator temperature suchy as suction pressure may comprise a bellows casing |56 in which is mounted a bellows for operating a plunger |51. The bellows casing |56 is connected by a pipe tothe suction pressure line of the refrigerating apparatus. The .plunger |51 is therefore operated in accordance with changes in suction pressure or evaporator temperature. 'I'he plunger |51 operates a lever. |58 fulcrumed on a knife edge |59. The lever |58 is provided with an ear |60 to which is sean adjustable spring |90, one end of the spring |90 being connected to the lever |86 and the other e'nd 'being connected to a nut |9| screw-- threadedly mounted on a' screw |92. By rotating the screw |92 the tension of the spring ture it is moved in a counter-clockwise direction. Stops |93 and 94 carried by the bracket |83 are utilized for limiting the amount of movement oi.' the lever |88. For purposes of illustration it is assumed that when the temperature within the compartment increases to 41 the lever |86 is moved against the lower stop |94 as illustrated in Figure 3 and when the temperature decreases to'40 .the lever |86 is moved Iagainst the-upper stop |93 as illustrated in Figure 4.

An arm |96 is pivoted to the bracket |64 by a pin |91 yand carries an abutment surface |98 to be engaged by the lever |58. The arm |96 is urged'in a counter-clockwise direction by an ady certain conditions to limit the counter-clockwise limiting movement of the pivoted lever |58. Upon an increase in suction pressure the lever |58 is moved in a counter-clockwise direction and upon a decrease in suction pressure the lever |58 is moved in a clockwise direction.

' The lever |58 is provided with an extension |88 and an arm |69 is pivoted to the extension |68 by a pivot pin |10. The extension |68 is prof vided with a lug |1| which is normally engaged by the arm |69. The extension |68 is provided with another lug |12 and the arm .|69 is provided with a lug |13, a spring |14 being connected between the lugs |12l and |13 to urge the arm |69 into engagement with the lug I1| as shown in Figure 3. The arm 69 therefore normally moves coextensively with the'exterision |68, the spring |14 providing a strain release the` purpose of which will be pointed out more fully hereafter. The arm |69 carries a pin |15 for operating the switching mechanism |54.

The switching mechanism |54 may comprise 1 a switch carrier |11, pivoted at |18 for carrying a` mercury switch |19. The lower end of the carrier "|11 is provided with two arms |80 and,

|8| to be engaged by the pin |15. When the pin |15 is moved tothe left and engages the arm |80 to move the carrier |11, the mercury switch |19 is moved to'a closed position and when the pin with a bulb f|85 which may be located within ,the enclosure to be' cooled. The bulb |85 may be charged witha volatile iiuid so vthat the bel- "lows 82 is expanded and. contracted in accordmovement o'f the arm ,|96 as is evidenced in Figure 3.5 However, when the latch member |88 is retracted' as'shown .in Figure 4 the-,movement of the arm |96 by the spring |99 is not limited.

A'I 'he lcontrol device |52 responsive to head pressure, -that is, the pressure on the high pressure side of the refrigerating apparatus, may comprise a bellows casing 205 in which'is mounted a'bellows for operating a plunger 201. The bellows casing' 205 is connected bya pipe to the high pressure line of the refrigerating apparatus so that the bellows within the casing 205 is expanded and contracted in accordance with changes V'in head pressure. A spring is also lo-` l t cury switch |19 is'closed a circuit is completed.

ance with changes in temperature. vThe bellows s |82 operates a lever v|86 pivoted at' |81 to the bracket |64 and rprovided witha latch membe@t |88. The lever |86 is urged in a counter-clockfrom the line wire 2|4 through the vmercuryk switch 19, wire 2| 5 and theA compressor motor back .to the other line wire 2 I3 to cause operation of the compressor motor and hence operation of the refrigerating apparatus.-

Omitting for the time being the operation 0f the head pressure responsive controller |52 let it be assumed that the parts are in the position shown in Figure 3. The mercury switch |19 is open and hence the compressor isnot operating. The temperature within the compartment has increased lio-41ov to cause the latch member |88 to engage the arm |96. Since the compressor is not operating the suction pressure withirf the refrigerating apparatus is increasing to move the lever |58 in acounter-clockwise direction. When the lever |58 engages the abutment surface |98 'be assumed that the suction pressure is 30 lbs.

As the suction pressure increases from 30 lbs. to 33 lbs. the lever |58 is moved in a counter-clock wise direction against the'action of both springs .|6| and |99. When the pressure iinally reaches 33 lbs. whereupon the lever |58 is moved into engagement with the lower stop |66, the pin |15 carried by the arm |69 closes the mercury switch |19 and the compressor is placed in operation. Immediately upon placing the compressor in operation the suction pressure starts to decrease and when the suction pressure decreases to 30 lbs. the lever |58 assumes the position shown in Figure 3. At this point the tension spring Cil |99 becomes ineffective to move vthe lever |58 in a clockwise direction since the arm |96 is limited in yits movement by the latch member |88. Accordingly only one spring |6| is then urging the lever |58 in a clockwise direction about the pivot |59. When the suction pressure decreases to 16 lbs. the lever |58 starts to move in a clockwise direction about the pivot |59 under theiniluence of the spring |6| and when the pressure finally decreases to lbs. the-lever |58 is moved into engagement with the upper stop |65 whereupon the pin |15 carried by the arm |69 opens the mercury switch |19. The compressor is then stopped and the suction pressure starts to rise.

When the suction pressure rises from 15 lbs. to

16 lbs. the lever |58`moves from the upper stop |65 into engagement with the abutment surface |98 as shown in Figure 3. A further ris in suction pressure is then resisted by both springs |6| and |99 and the lever will not move from the position shown in Figure 3 toward the bottom stop until such time as the suction pressure starts rising above lbs. Thus when the temperature within the enclosure is at 41 and ca'lling for cooling the compressor is started only when the suction pressure increases to 33 lbs.

and remains in operation until such time as the suction pressure decreases to 15 lbs. Y If after the compressor has been started in the troller |5| or the head pressure controller |52 it manner outlined immediately above and `is ops erating to reduce the pressure on the low pressure side of the refrigerating apparatus the temperature responsive controller |53 'should become satisfied before the suction pressure is decreased to 15 lbs. then the latch member |88 is moved out of engagement with the arm |96. If the suction pressure should be below for ,example 27 lbs. both springs 6| and |99 will become effective to move the lever |58 in a clockwise direction to the upper stop |65 to -open the `inercury switch |19 and the compressor will then be stopped. 9

Assume now that the temperature within'the compartment is whereupon thelever |86 is moved against the upper stop |93 and the latch member |88 is'retracted. `When the suction pres- .Y

sure increases to 33 lbs. both springs |6| and |99 are overcome and the lever |58 is moved against the lower stop |66 to close the mercury switch .|19. The compressor is then placed in operation y and the suction pressure is caused to decrease.

As thesuction pressure decreases from 33 lbs. the lever |58 moves in a clockwise direction underA vtion pressure controller.

springs |,6| and |99 stilltend to urge the lever |58 in a clockwise direction. When the suction pressure decreases to 27 lbs. the lever |58 is moved against the upper stop by both springs |6| and |99 and the mercury switch |19 is opened. The compressor is then stopped and cannot be restarted until such time as the suction pressure rises to 33 lbs. to allow the lever |58 to engage the lower stop |66to reclose the mercury switch |19.

Assume now that the parts are in the-position shown in Figure 4 with the mercury switch v,|19 closed and the compressor in operation. If now the head pressure or the pressure on the high pressure side of the refrigerating apparatus should increase to a predetermined high value illustratively 180 lbs., the`plunger 201 will engage the upper end of the lever 208 to move the lever 208 in a counter-clockwise direction. Counterclockwise movement of the lever 208 will cause engagement with the lug 2|| of the arm |69 to move the mercury switch |19 tothe "oiT position, this movement being permitted by the strain release connection afforded by the spring |14 located between the lugs |12 and |13. Thus when the pressure on the high pressure side of the reuntil such time as the suction pressure rises to 33 lbs. due to the differential action of the mercury switch |19 and the lost motion connection between the pin |15 and the arms |80 and |61. 10v

Thus it will be seen that when the mercury switch |19 is opened either by the suction pressure concannot again be reclosed until such time as the suction pressure rises to 33 lbs. or the head pressure decreases to 140 lbs.

The operation of the arrangement shown in Figures 3 and 4 may be summarized briey as follows. When the temperature within the enclosure is below a predetermined value, illustratively 40, the compressor may be started only when the suction pressure increases to 33 lbs. and

the head pressure decreases to 140 lbs., and after the compressor is once started it will remain in operation until such time as either the suction pressure decreases to 27 lbs. or the head pressure increases to 180 lbs. Thus the refrigerating apparatus is intermittently operated by the suc- The temperature responsive control device |53 is incapable in itself of starting operation of the rcfrigerating apparatus. If after the refrigerating apparatus is started by the suction pressure control device |5|, the temperature responsive control device 53 should demand cooling upon an increase in enclosure temperature to 41 the compressor will be maintained in operation until either the temperature within the enclosure should decrease to 'J a npredetermined value, illustratively 40, or the suction pressure should decrease to a predetermined low value, illustratively l5 lbs., or the pressure on the high pressure side of the refrigerating v apparatus kshould increase to a predetermined high value,` illustratively lbs. Upon stopping of the compressor by the occurrence of any of these conditions it cannot be restartedr until such time as the suction pressure rises to 33 lbs. and the head pressure decreases to 140 lbs.

Referring now. to Figure 5, the same control only difference being that a different temperature responsive control means 252 is utilized in 'arrangement |50 is utilized as-in Figure 3, the 3 place of the temperature responsive control means |53 ofv Figure 3. Accordingly, in Figures 3 and 5 like reference characters are utilized for like parts. The temperature responsive control means 252 of Figure 5 may comprise an electrical operating coil 258 carried byu a bracket 254, the bracket 254 being provided withA upper and lower stops 255 4and 256.

When the operating coil 253 is4 medium being controlled. Air under pressure4 utilized for operating the lever |86.for in turn operating the latch member |88. The bracket 215 is provided with'upper and lower stops 216 and 211 for limiting the movement'of the lever |86. The pneumatic bellows 214 is connected by a branch line 218 to a pneumatic thermostat '.219 responsive to the temperaturev of'the is supplied to the pneumatic thermostat 218 by an air supply pipe A280. When the temperature within the space being controlled rises to 41 the pneumatic thermostat 218 supplies air through the pipe -218 to the bellows 214 to cause the latch member |88 to engage the lever |86. l When the temperature decreases to 40 the pneumatic thermostat 218 vents the air from the bellows 214 through the branch line 218 to allow the lever |86 to move against the upper volatile fluid for operating a lever 262 against the action of an adjustable tension spring 263 for operating a mercury switch 264. Forv purposes of illustration it is assumed that when the temperature ofthe bellows 26| rises to 41 the mercury switch 264 is closed and when the temperature decreases to 40"` the mercury switch.

264 is opened.

Power is supplied to the operating coil 253 byl means of wires 265 and'266 connected across wires 2|3 and 2|5,'the operating coil 253 thereby being connected in parallel with the compressor motor. When'the temperature condition affectstop 216 to release the latch member |88 from the` lever |96. Accordingly the modification shown in Figure 6 operates in exactly the same manner as the modification shown in Figure 3 and therefore va .more complete description of this modification is not considered necessary. l

Although for purposes of illustration several forms of this invention have been disclosed, other forms thereofl may become apparent `to those skilled in the art upon reference to this dis. closure and therefore this invention is to be lim- -ited only by the scope of the appended claims.

.I claim as my invention:

ll. In a refrigeratingappar'atus having evap# o rator means for controlling the condition of a ing the thermostat 260 rises to 41 to closey Ithe mercury switch 264 and when the mercury switch` |18 is closed, a circuit is completed from the line wire 2|4 through mercury switch |18, wires 2|5 and 265, mercury switch264, wire 261,'operating coil 253, and wire 266 backv to the other ating coil 253. When the-operating coil 258 is energized the latch member |88 engages the lever |86 and the control arrangement'vof Figure 5 operates in exactly the same way as the control arrangement of Figure v3. 'When the temperature4 aectingthe bellows 26| decreases to 40 the circuit through the operating 'coil' is broken and the latch member |88 disengages the lever |86 to cause the control arrangement of Figure 5 to operate in the same manner as the vline wire 2|3 to cause energi'zation of the opermedium and a mechanismY for controlling the circulation of refrigerant through the evapo- `rator means, the combination of, control means responsive to a condition which is a measure of evaporator temperature, control means respon- -sive to the condition of the medium controlled lby the evaporator means, and'means controlled by both control means for controlling the mechanism tostart circulation of refrigerantthroughthe evaporator means onlywhen the evaporator .temperatureincreases to a predetermined high value, tol continue circulation of refrigerant through the evaporator means when the` condition of the medium controlled by the evaporator means is below a predetermined value until the evaporator temperature decreases Ito a predeter mined low value or to continue circulation of I refrigerant throu'ghthe evaporator means as vcontrol arrangement of Figure 3. Accordingly, a more thorough description of the operation -of the control arrangement of Figure 5 is not considered necessary. Since the operating cit-cuit for the operating. coil 258 passes through the mercury switch |18, the operating coil 2581s not ,i called uponv to operate the latch member l| 88 T until -the'leverl86 is moved to the lower position to allow free movementof the latch me'mber |88.

the operating coil 253 may be made smaller.

' Referring now t6V mure 6, the-'control ar-y rangement |50 fis exactlyjthe same as thatof Figure -with the' vciiceptionthat a different temperature responsive control means- 218l is substituted for the temperature responsive, conlong as the condition'ofl the medium controlled by the evaporator means is above said predetermined value j regardless of whether-the evaporator temperature decreases below the predetermined low value.

2. In a refrigeratlng apparatus .having evaporator means for controlling the condition of a medium anda mechanism for controlling the cirjsoemanen of refrigerant through'tne evaporator means, the combination of, first control means responsive to a condition which isa measure-of evaporator temperature for controlling the mechanism to start circulation or refrigerant through the evaporator, means only when. the evaporator temperature risestol a predetermined high value ,v-@and to stop circulation of refrigerant through the evaporator means when the evaporator tem- Iperature decreases to a predetermined` low value and second control means responsivetothe con'- trol means |53 of'Figure 3. In Figure 6 a pneumatie bellQWS '214 Gamed 'by a bracket 216 is 75 ue to maintain circulation of refrigerant through dition of the medium controlled by the: evaporator means for also controllingthemechanism when the condition rises to a vale means, the combination of, control means ren sponsive to a'condition which `is a measure of yevaporator temperature, control means responsive to the condition of the medium controlled by the evaporator means, and means controlled by both control means for controlling the mechanism to start circulation of refrigerant through tlie evaporator means only when the evaporator temperature increases to a predetermined high vvalue, to continue circulation of refrigerant through the evaporator means when the condition of the medium controlled by the evaporator means is below a predetermined value untilJ the evaporator temperature decreases to a predetermined intermediate value orto continue circulation of refrigerant through the evaporator means as long the condition of the medium controlled by the evaporator means is above said predeteris mined value provided theevaporator temperature does not decrease to a predetermined low value. 4. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and a mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, control means responsive to a condition which is a measure of evaporator temperature, control means responsive to the condition of the medium controlled the medium controlled by the evaporator mean.. for also controlling the mechanism when the condition rises to a predetermined value to maintain circulation of refrigerant through the evaporator 5 means after circulation has been started by the first control means regardless of whether the evaporator temperature decreases below the predetermined low value, said second control means being incapable of controlling said mechanism l to start circulation of refrigerant through the evaporator lmeans, and third control means responsive to the pressurefon the high pressure side of the refrigerating apparatus for controlling-said mechanism to stop circulation of refrigerant l through the evaporator means when the pressure increases to a predetermined high value.

6. In a refrigerating apparatus having evaporator 6means for controlling the condition of a medium anda mechanism for controlling-the circulation of refrigerant through the evaporator means, the combination of, control means responsive to a condition which is a measure of evaporator temperature, control means responsive to the conditio of the medium controlledI by the evaporator n? eans. means controlled by 'both control means for controlling the mechanism to start circulation of refrigerant through the evaporator means only when the evaporator temperature increases to a predetermined .high value, to continue circulation of refrigerant through the evaporator means when the condition of the medium controlled by the evaporator means is below a predetermined value until the evaporator temperature decreases to a predetermined intermediate value or to continue circulation of refrigerant through the evaporator means as long as the condition of the medium controlled by the evaporator means is above said predetermined Vvalue provided the evaporator temperature does by the evaporator means, means controlled by e40 not decrease to a predetermined low value, and

both control means -for controlling the mechanism to start circulation of refrigerant through the evaporator means only when the evaporator temperature increases to a predetermined high value, to continue circulation of 4refrigerant through the evaporator means when the condition of the medium controlled by the evaporator means is below af predetermined value until the evaporator temperature' decreases to a predetermined low value or to continue circulation of refrigerant through the evaporator-means as long as the condition of the medium controlled by the responsive to-a condition which is a. measure of- Y evaporator temperature for controlling the mechanism to start circulation of refrigerant through v they evaporator means only when the evaporator "temperature rises to a predetermined high value and to stop circulation of refrigerant through the evaporator meansl when the evaporator tempera"- ture decreases 'to `a predetermined low value, seccontrol means responsive to the pressure on the high pressure side of the refrigerating apparatus when the pressure increases toa predetermined high value. p 1

7. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and a mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, control means responsive to a condition which is a measure ofr evaporator means is above said predetermined evaporator temperature, control means responsive to theA condition of the medium controlled by the evaporator means, control means responsive to the pressure on the high pressure side of 'the refrigerating apparatus, and means controlled? by alluof the control means for controlling the mechanism to start circulation of refrigerant 6o through the evaporator means only when the evaporator temperature increases to a predetermined high value and the pressure ori'tliehigh pressureI side decreases to a predetermined low l value, to continue circulation of .refrigerant through the evaporator means when the condition of the medium controlled by the'evaporator means is below a predetermined value until either the evaporator temperature decreases to a pre- 7'0 determinedlow v'alue or the pressure on the high pressure side increases to a-predetermined high value nor to continue' circulation of refrigerant through the evaporator means as long as the condition of the medium controlled by the evaporaond control meansresponsive to the condition ci tor means is above said predetermined value unarras-isi 4 1 .9

less the pressure onthehiglr pressure side in# creases to 'said predetermined high value.

8. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and a mechanism `ior controlling the circulation of refrigerant through .the evaporator `means, the combination, of, control means re sponsive to a condition which is a measure of, evaporator temperature, control means responsive.

to the condition of the medium controlled by the evaporator means, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, and means controlled b-y *l all of the control means for controlling the mech-I' anism to start circulation of refrigerant through the evaporator means only when the evaporator temperature increases to a predetermined high value and the pressure on the high pressure side decreases to a predetermined low value, to continue circulation of refrigerant through the evaporator means when the condition of the medium controlled by the evaporator means is below a predetermined value until either the 'evaporator temperature decreases to a predetermined intermediate value or the pressure on the high pressure side increases to a predetermined high value or to continue circulation of refrigerant through the evaporator means as long as the' condition of' the medium controlled by. the evaporator meansV is above said predetermined value unless the pressure. on the high pressure side increases to said predetermined high value or the temperature of the evaporator means decreases to a predetermined low value. n Y

9. In a reirigerating apparatus having evaporator means for controlling the condition .oi a

medium and an electrically kcontrolled mechanism for controlling the circulation of refrigerant through' the evaporator means, the' combination of, first' switch means, means responsive to the kcondition of the medium controlled by the evaporator means for closing the rst switch means when the condition increases to a predetermined highvalue, second switch means, meansrespon.-

sive to a'condition whichis a measure of evapo rator temperature for closingfthe second switch means when the evaporator temperature increases to a predetermined highvalue, means for completing a lstarting circuit through the second switch means independently of the iirst switch v means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means. a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through the iirst switch means and the maintaining. switch independently of the second switch means to main-4 tain the electricallyl controlled mechanism in operation to circulate refrigerant through the evap- 60 orator means. said maintaining switch remaining closed as long as the maintaining circuit is completed..

10. In a refrigerating apparatus having evaporater meansfor controlling the condition of a medium and an electrically controlled mechanism for controllingl the circulation ofrefrigerant through the evaporator means, the combination of, ilrst switch means, means responsive tol the condition of the medium controlled bythe evaporator means for closing the ilrst switch `means when the condition increases'to a predetermined high value, second switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increasesl to a predetermined high value, .third switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus 5 for4 opening the third switch means when the pressure increases to'a predetermined high value,

means forcompleting a starting circuit through Nthe, second switch means independently of the lilrst switch means to operate the electrically l0 controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switch, means for closing-the maintaining switch as an incident to completion ofthe starting circuit, means Ior completing a maintaining circuit `through the nrst switch means, the uurd switch means and .the maintaining switch independently ot the second switch means to maintain the electrically controlled mechanism in operation vto circulate refrigerant through the Levaporator means, said maintaining switch remaining closed as long as the maintaining .circuit is completed.

1l. In a refrigerating apparatus having evaporator means for controlling .the condition of a 4medium and an electrically controlled mecha- 5 nism for controlling the circulation of refrigerant through the evaporator'means, 'the combination. of, rst switch means, means responsive to the condition oi the medium controlled by the evaporator meansior closing the rst switch means when the condition increases'to a predetermined high value,."second and third' switch means,

-n means responsive to a condition which is a meas,

ure ofevaporator temperature for closing the second switch means,whenV the evaporator 0ternperature increases to a predetermined high value and for opening the third switch ,means when the evaporator temperature decreases to a predevterm'ined low value, means for completing a starting circuit throughthe second switch means'in- 0"depen'dently of the rst switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switch,- means -for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through theiirst and third switch means and the maintaining switch/independently of the second switch means to maintain the electrically controlled'mechanism in operationtofcirculate refrigerant `through the evaporator means;

said maintaining switch remaining closed as vlon'g Aas the maintaining circuit is completedf, y*

1,2. In a refrigerating apparatus having evaporator means for 'controlling the condition of a medium andan electrically controlled mechazo startingl circuit through the scond'syvitch means v independently of the iirst switch means-Ato operate ,the electrically controlled mechanism to circulate,

` refrigerant through the evaporator means,V a

maintaining switch, means for closing the main- 'I5A Itaining switch as an incident to completlongof the starting circuit, means for completing a first maintaining circuit throughl the third switch means and the maintaining switch independently of the first and second switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, and means for completing a second maintaining circuit through the first switch means and the maintaining switch independently of the second and third switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said'maintaini'ng switch remaining closed as long as either maintaining cir,- cuit is completed. h f

13. In a refrigerating apparatushaving evaporator means for controlling the condition of a medium and an electrically controlled mechanism for'controlling the circulation of refrigerant through the evaporator means, they combination of, first switch means, means responsive to the' condition of the medium controlled bythe evaporator means for closing the rst switch means when the condition increases to apredetermined high value, second, third and fourth switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increases to a. predetermined-high value, for openingthe third switch means when the evaporator temperature decreases to a predetermined intermediate value and for of the first and second switch means to maintain the electrically controlled mechanism inoperation to circulate refrigerant through the eva orator means, and means for completing a seco d maintaining circuit through the first and fourth switch means and the maintaining lswitch independently of the second and third switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as either maintaining 'circuit is completed.

14. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, first switch means, means responsive to the condition 'of the medium controlled by the evaporator means for closing the first switch' means when the condition increases to a predetermined` high value, second switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increases to a predetermined high value, third and fourth switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the third switch meansA when the pressure decreases to a predetermined low value and for opening the fourth switch means when the pressure increases v to a predetermined high value, means for completing a starting circuit through the second and third switch means independently of the first switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switchfmeans for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through the first and fourth switch means and the maintaining switch independently of the second and third switch means to maintain the electrically controlled mechanism in operation to circ ulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as the maintaining circuit is completed.

15. In a. refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator mea'ns, the combination of, rst switch means, means responsive to the condition of the medium controlled by the evaporator means for closing the first switch means when the condition increases to a predetermined high value,v second and third switch means, means responsive to a condition which is y value and for opening the third switch means when the evaporator temperature 'decreases to a predetermined low value, fourth switch means, means responsive' to the pressure on the high pressure .side of the refrigerating apparatus for opening the fourth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through thesecond switch means independently of the rst switch means to'operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through the first, third and fourth switch means and the maintaining switch independently of-the second switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as -long as the maintaining circuit is completed.

16. In a refrigerating apparatus having evaporator means for controlling the condition of a medilun and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, first switch means. means responsive to the condition of the medium controlled by the evaporator means for closing the first switch means when the condition increases to a predetermined high value, second and third switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second'switch means when the evaporator temperaturel increases to a predetermined high value and for opening the third switch means when the evaporator temperature decreases to Aa predetermined low value, fourth switch means, means responsive to the' pressure on the high pressure side of the refrigerating apparatus for opening the fourth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through `the second switch means independently of the first switch means to operate the electrically controlled mechanism to' circulate refrigerant through the evaporator means, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a first maintaining circuit through the third switch means and the maintaining switch independently of the first and second switch means to maintain the elec- 'trically controlled mechanism in operation to circulate refrigerant through the evaporator means, and means for completing a second maintaining circuit through the first and fourth switch means and the maintaining switch independently of the second and third switch means to maintain the electrically controlled mechanism in operation to circulate; refrigerant through the evaporator means, said maintaining switch remaining closed as long as either maintaining circuit is completed.

17. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, rst switch means, means responsive to the condition ofthe medium controlled by the evaporator means for closing the first switch means when the condition increases to a predetermined high value, second, third and fourth switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increases to a predetermined high value, for opening the third switch means when the evaporator temperature decreases to a predetermined intermediate value and for opening the fourth switch means when the evaporator temperature decreases to a predetermined low value, fifth switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for opening the fifth switch means when the pressure on the high pressure side increases to a -predetermined high value, means for completing a starting circuit through the second switch means independently of the first switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switch, means for closing the maintaining switch 2s an incident to completion of the starting circuit, means for completing a first maintaining circuit through the third switch means and the I maintaining switch independently of the first and second switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, and means for completing a'second maintaining 4circuit through the first, fourth and fifth switch means and themaintaining switch independently of the second and third'switch means to maintain the electrically controlled mechanism ln operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as either maintaining circuit is completed. f

18. In a refrigerating apparatus having evap- 4 orator means for controlling the condition of a medium and an electrically controlled mechanism for controlling they circulation of refrigerant through the evaporator means, the combination of, first switch means, means responsive to the condition of the medium controlled by the evaporator means for closing the first switch means when the condition increases to a predetermined high value, second and third switch means, means responsive to` a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increases to a predetermined high value and for opening the third switch means when the evaporator temperature decreases to a predetermined low value, fourth and fifth switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the fourth switch means when the pressure decieases to a predetermined low value and for opening the fifth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through the second and fourth switch means independently of the first switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporatormeans, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through the first, third and fifth switch means and the maintaining switch independently of the second and fourth switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as the maintaining circuit is completed.

19. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electricallyv controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, first switch means, means responsive to the condition of the medium controlled by the evaporator means for closing the' first switch means when the condition increases to a predetermined high value, second and third switch means, means responsive to a condition which is a measure cf evaporator temperature for closing the second switch means when the evaporator temperature increases to a predetermined high value and for opening the third switch means when the evaporator temperature decreases to a predetermined low value, fourth and fifth switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus.

forclosing the fourth switch means when the pressure decreases to a predetermined low value and for opening the fifth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through the second and fourth switch means independently of the first switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a main-f taining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a first maintaining circuit through the third and fth switch means and the maintaining switch independently of the first, second and fourth switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, and means for completing a second maintaining circuit through therst and fifth switch means and the maintainingV switch independently of the second, third and fourth switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as either maintaining circuit is completed.

20. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically .controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, first switch means, means responsive to the condition of the medium controlled by the evaporator means for closing the rst switch means when the condition increases to a predetermined high value, second, third and fourth switch means, means responsive to a condition which is a measure of evaporator temperature for closing the second switch means when the evaporator temperature increases to a predetermined high value, for opening the third switch means when the evaporator temperature decreases to a predetermined intermediate value and for opening the fourth switch means when the evaporator temperature decreases to a predetermined low value, fifth and sixth switch means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing,

the fifth switch means when the pressure decreases to a predetermined low value and for opening the sixth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through the second and fth switch means independently of the first switch means to operate the electrically controlled mechanism to circulate refrigerant through the evaporator means, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a first maintaining circuit through the third and sixth switch means and the maintaining switch independently of the rst, second and fifth switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, and means for completing a second maintaining circuit through the first, fourth and sixth switch means and the maintaining switch independently of the second, third and fth switch means to maintain the electrically controlled mechanism in operation to circulate refrigerant through the evaporator means, said maintaining switch remaining closed as long as either maintaining circuit is completed.

21. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, switch means movable to on and oi positions for controlling the electrically controlled mechanism, a control device responsive to a condition which is a measure of evaporator temperature, spring means for opposing operation of the control device, means controlled by the control device for moving the switch means` to the on position to circulate refrigerant through the evaporator means when the evaporator temperatur'e increases to a predetermined high value and to the off position to stop circulation of refrigerant through the evaporator means when the evaporator temperature decreases to a low value, and a control device responsive to the condition of the medium controlled by the evaporator means for regulating the spring means to cause the switch means to be opened at a lower evaporator temperature value when the condition of the medium is above a desired value than when the condition of the medium is below the desired value.

22. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of, switch means movable to closed and open positions for controlling the electrically controlled mechanism, a control device responsive to a condition which is a measure of evaporator temperature for closing the switch means upon an increase in evaporator temperature and a pair of spring means opposing said control device for predetermining the evaporator temperature value at which the switch means is closed to circulate refrigerant through the evaporator means and for opening the switch means to stop circulation of refrigerant through the evaporator means when the evaporator temperature decreases, and a control device responsive to the condition of the medium controlled by the evaporator means for preventing one of the spring means from opening the switch means when the condition of the medium is above a desired value to cause the switch means to be opened at a lower evaporator temperature than when the condition of the medium is below the desired value and both spring means are effective to open the switch means.

23. In a refrigerating apparatus having evaporator means for controlling the condition of a medium and an electrically controlled mechanism for controlling the circulation of refrigerant through the evaporator means, the combination of switch means movable to on and 01T positions for controlling the electrically controlled mechanism, a control device responsive to a condition which is a measure of evaporator temperature, spring means for opposing operation of the control device, means controlled by the control device for moving the switch means to the on position to circulate refrigerant through the evaporator means when the evaporator temperature increases to a predetermined high value and to the off position to stop circulation of refrigerant through the evaporator means when the evaporator temperature decreases to a low value, a control device responsive to the condition of the medium controlled by the evaporator means for regulating the spring means to cause the switch means to be opened at a lower evaporator temperature value when the condition of the medium is above a desired value than when the condition of the medium is below the desired value, and a control device responsive to the pressure on the high pressure side of the refrigerating apparatus for moving the switch means to the off position whenever the pressure increases to a predetermined high Value.

24. In a control device, in combination, a control member movable to first and second operative positions for performing a control function, first and second spring means urging said member toward said first position, automatic means for moving said member in opposition to said spring means to said second position, control means cooperative with one of said spring means in a manner to render it ineffective to urge said member towards said first position and automatic means for operating said control means.

ALW'IN B. NEWTON.

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