US2364459A - Control of refrigeration apparatus - Google Patents

Description

Dec. 5, 1944. w. l. MCGRATH CONTROL OF REFRIGERATION APPARATUS Filed Oct. 25, 1941 2 Sheets-Sheet 1 INVENTOR.

William. L. Mrah..

Dec. 5, 1944.

CONTROL OF REFRIGERATION APPARATUS w. L. MCGRATH 2,364,459

Filed oct. 25. 1941 2 snms-sheet` 2 rZGZ :gam

William MS Grah...

BY` /w Albi-neg" A Patented Dec. 1944 CONTROL yOF REFRIGERATION APPARATUS William L. McGrath, Philadelphia, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware ,Application October 25, 1941, 'Serial No. 416,530

(Cl. (i2- 4) 16 Claims.

lthe control mechanism will return to an initial position from which it will recycle upon resumption of the'power supply before any compressors are reenergized.

Another object is to provide manual shut-down' means whereby upon a manual shut-down the control mechanism will automatically return to an initial position, but one compressor nevertheless pumping down the evaporator just as in the event of an automatic shut-down.

'I'he details of my invention and numerous other of its objects and advantages will become .apparent from the following description` and drawings, wherein:

Fig. 1 represents a preferred form of my invention, and y Fig. 2 represents a modified and simpler form of the invention. l

Referring ,to Fig. 1 of the drawings, number Ill-designates a duct, the right end of which is connected to the suction side ofa fan disposed withina housing I I. Air for conditioning aspace I2 is circulated through ductI I0 and discharged into the space by means ofthe fan. The air may be amixture/of outdoorair-and recirculated air in accordance with common practice.

Disposed in the duct` I0 is a heat exchanger vcir-coil I3 through'whicli c old water is passed for cooling the air, the cold water being admitted to the` coil through a pipe I4. Interposed in the pipe I4'is an electric solenoid type control valve I5.

Also disposed in the duct I0 is an evaporator designated by the numeral I8 forming ,part of a direct expansion refrigeration system. The refrigeration system comprises three'com'pressors I9, 20 and 2| which discharge into a commonA header 22 through pipes 23, 24, and 25 respectively. The header 22 is connected to a condenser 26. The condenser is connected to the evaporator i8 by a pipe 21, and interposed in the pipe 2'l-is an electric solenoid type stop valve 28 and also a thermostatic valve 29. The thermostatic valve 29 is of the usual type constructed and arranged to maintain a constant degree of superheat at the outlet of the evaporator/ The evaporator outlet is connected to a pipe 30 which is connected to the inlet of all the compressors I9, and 2i. The operating mechanism of the valve 29 includes an expansible chamber which is connected to'a thermal bulb 32 by means of a capillary'tube 33, the thermal bulb being disposed in intimate heat exchange relationship with the pipe connected to the evaporator outlet.l The thermal bulb 32 is filled with an expansible liquid which vaporizes, the gas expanding and contracting in accordance with the temperature in the outlet pipe 30.

The controls for the compressors constitute primarily a step controller designated by the numeral 38. The step controller 3B includes a reversible electric motor 39 having rotors 4IJ` and 4I mounted on a shaft 42 and having windings 43 and 44 respectively associated with the rotors. The motor 39 drives a shaft 46, this shaft preferably being driven through a gearv train at a slower speed than the speed of the shaft 42.

Mounted upon the shaft 46 is a plurality of cams y 4l, 48, 49, 50, and 5I. The cam 4l has a single dwell of relatively short angular extent, and this dwell is arranged to actuate a pivoted switch carrying lever 54, which carries a mercury switch 55. When the cam 41 is in the position shown on the rdrawings, the dwell engages the lever 54 tilting the mercury switch 55 to closed positionas shown. .Each of the cams 48 to 5I has a single dwell of substantially 180 angular extent, the dwells on the different cams`I being spaced relatively-as shown yon the drawings. Each of.

the cams da to 5| has a pivoted switch'carrying lever associated therewith, these levers being designated by the numerals 56,51, 58, andI 59 respectively, the levers carrying mercury switches 60, 6I, 62, and 63, respectively. When the shaft 46 is rotated in a counter-clockwise direction, the dwells on thecams will engage their respective ly closed only when the shaft 46 is in substantial- 1y initiall position. After switches 60 to 63 have been closed, and the shaft 46 is rotated in a clockwise direction, the switches are opened in sequence from right to left in a reverse manner. The windings of the motor 39 vare controlled primarily. by a proportioning type thermostatic controller 55 comprising a bimetal 'element 66 5 arranged to actuate `a slider 61 which sweeps across a. resistance 68 when the temperature affecting the element 66 rises and falls. The controller 55 is arranged to operate over a range of 2f', the slider B1 being Yat the upper end of re- 10 sistance 68 when the temperature is 70 F., and being at the lower end of resistance 68 when the temperature rises to '72 F.. The controller 65 controls the windings ofthe motor 39 through a mouse-trap relay 10 comprising a vUshaped l5 armature 1| having legs 12 and 13, there being a winding 1|| associated with leg 12 and a winding 15 associatedY with leg 13. The amature 1| is pivoted at 16 and it carries a switch blade 11 movable between iixed electrical contacts 18 and 20 19. When the windings M and 15 are equally energized, the magnetic pullexerted on legs 12x and 13 isequal and the armature assumes a balanced position whereinthe switch blade 11 is equally distant Abetween the contacts 18 and *19; 25 When the energization of winding 14 preponderates over that'of winding 15, the magnetic. pull on leg 12 exceeds that on leg 13,.an'd the armature 1| is rotated in a clockwise direction causing blade 11 to engage contact 18.' When the ener- 30 gization of winding 15' preponderates over that ofwinding 14, 4the magnetic pull on leg 13 is greater than that on leg 12 and armature 1| is rotated in a counter-clockwise direction, causing. sw}tch blade i-1 .to engage.contact"|9.l The con- '3 5 trolsfor .the ,windings of motor 39 also include a rebalancing potentiometer comprising a resistance 8| having ,associated therewith a slider 82 which is mounted on ashaft 83 driven by the motor 39. .In practice, the shaft 83 is drivenA 40 through a gear train so as to operate ata slower speed than the shaft 42; the slider 82 may-of course be mounted on the shaft 46. l Also mounted on the shaft 46 is a switch actuating iinger 8'5 arranged to actuatelimit switches 45A 86 and 81, the limit switches `85 and 81 being in circuit with the windings 44 and 43, respectively, so as to interrupt the circuit through the motor windings'whenever the shaft 46 has been driven to a limiting .position in either direction. The 50 .switch B8 comprises blades 88 and 89 carrying -contacts 90 and 9|, respectively,l which are normally in engagement, .the blade y88 having an extending 4portion which may be engaged by the finger 85 or opening .the switch 86 when the 55 Ashaft 46 has been rotated substantially 180 in a counter-clockwise direction from the position in which itzis shown on the drawings. Switch 81l comprises blades 93.and94 carrying contacts 95 and 96,'respectively, which are normally in en- 60' gagement, the blade 93 having an extending portion which is adaptedito he engaged by the finger 85 when the'stepcontroller is in initial position asshown for opening'the switch 88.'. f

Power for the ,proportioning control'isystem is e5 supplied'by'a step-down transformer 98 comf fprisingak primary winding 99 and a secondary winding |00, the secondary win'ding having a fewer number of turns than the primarywinding. Power is' supplied to the primary winding 70 through wires |0| and '|02 connected to` any suitable Source of power not shown.

Numeral |ll3deslgnates a manual switch blade. vcooperating witha iixed electrical contact |04.

This switch-controls the winding 15 and, as will 15.*l

lpresently be described, is ,operable to cause the step controller to return to initial position. The details of operation of the. step controller in response to the proportioning controller 65 will be pointed out in the description of operation hereinafter wherein all of the various 'electrical circuits Will be traced. I Y

The controls for the various compressor motors include a power failure relay designated by the numeral |05, this )relay having a winding |06 with which is associated an armature connected to switch blades |01 'and |08 which are moved vinto engagement with iixed .electrical contacts |09 and lill", respectively, when the winding is energized. The power failure relay ||l5 is normally energized as will presently be pointed out, and controls the 'power supplied to all -oi the compressor motors.

Numeral ||5 designates another relay which, as will be presently pointed out, controls only the motor of compressor |9, the relay ||5 comprises a winding IIB 'having an armature .associated therewith connected to switchblades ||1 and |'|'8 which are vmoved to the left intoengagement withv fixed electrical'contacts ||9 and |20, -respectively, by the armature when the winding I6 is energized.

Numeral 22 designates another relay which controls the relay ||5, the relay` |22.comprsing a winding |23 having an armature associated therewith connected to a movable switch blade |24 which is moved to the left intoI engagement with the fixed electrical contact l2 5.by the armature when the winding |23 is energized.

The motor of compressor |9 is controlled by a relay or starter |26 comprising a winding |21 having an armature associated therewith con-` nected to a movable switch blade |26, which is moved to the left into engagement with the ixed electrical contact |29 by the armature when the winding |21 is energized. The motors of compressors 20 yand 2| are controlled by relays or starters |26a and |2617 which are identical with the relay |26, the elements, being similarly num-v bered with identifying characteristic letters a and b, so that further description of these relays is not necessary.

Numeral |3| designates a controller of a type disclosed in detail in the patent to Judson, No. 2,255,666.I The controller |3| comprises a switch mechanism responsive to head pressure and suction pressure of the refrigeration system, the suction pressure responsive mechanism of the controller being connected to the pipe 3D by means of tubes |32 and |33. The head piessure responsive mechanismo'f the controller |2I is connected to the pipe 21 `by a tube |34. The controller |3| is l arranged to close the circuit therethrough .when

the suction pressure .risesto a predetermined rela tively high value and the head pressure falls to a predetermined relatively low value. Thementroller |3| is arranged to interrupt the 'circuit therethrough when the suction pressure falls to a predetermined relatively low value or ,when the headgpressure rises to a predetermined relatively high value. Thus, theV controller |3| acts as a limiting controller' opening its circuitA when the head pressure is relatively high to` preventoverloading the compressor motors, it being\ under stood that the controller |3| controls the supply of power tov the compressor motors. The controller |3| also'acts asa limit controller in that itcuts ofi the supply of power .to the compressors whenthe suction pressure is relatively low and closes 'the circuit to supply power only when the suction pressure rises to a relatively high value.

Numeral |36 designates a suction pressure responsive switch comprising an expansible bellows I31 cnn`ected to pipe 30 through tubes |33 and |38. The movable end of the bellows carries an operating stem into engagement with which a switch carrying lever |39 is normally urged by a coil spring |40. The lever |39 carries a mercury switch |4Ifhaving electrodes at its left end which become bridged when the suction pressure is above a predetermined relatively high value at which the bellows |31 isin an expanded position. When the suction pressure falls to a predetermined relatively low value, the Ibellows |31 contracts moving lever |39 in a clockwise direction and opens the switch I4I;

With the parts in the position shown, the step controller 38 is in initial position, the temperature `in space I2 being at a relatively low value of 70, for example, at which cooling is not required and at which the slider 61 is at the upper end of.resistance 68. The slider 82 of the balancing potentiometer is at the clockwise end of' resistance 8|. The valves |5 and 28`are closed, and inasmuch as the step controller is in initial position, the mercury switch 55 is closed so as to complete a circuit for the power failure relay |05 as follows: from line conductor |6| 'to wire 60,

controller |3|, wire |59, wire |58, mercury switch 55, wire |51, wire |56, wire |55, wire |54, winding |06, wire |53, wire |52, and wire |5| back to line conductor |50, the line conductors |58 and |6| .being connected to any suitable source 0f power. not shown. When relay |05 is energized, blades |01 and I08-engage their respective flxed contacts, engagement of blade |08 with contact |I|l completing a maintaining circuit for relay |05 which is independent of mercury switch 55, this circuit being as follows: from line conductor |6| to wire |60, controller |3|, wire |59, wire |48, contact IIO, lblade |08, wire |49, wire |54, winding |06, wire |53, wire |52, and wire |5| back to line conductor |50. It is understood that the switch mechanism of controller I|3| is in closed position, the suction pressure at this time being at a relatively high value and the head pressure being ata low enough value so as not to cause overloading of the compressor motors upon starting.

With the parts in the position shown, the windings 14 and 15 are equally energized so that the blade. 11 is equally distant Vbetween contacts 18 y anld 19. The circuit for winding 14 is as follows:

,circuit for winding 15 is as follows: from secondary to wre I 62, wire I|63, element 66, slider 61, resistance 63, wire |69, contact |04, switch blade |03, wire |10, contact |09, switchvblade |01, wire |1|, winding 15, wire |12, slider 82,

cuit of winding should be interrupted by either of thefsaid switches the energization of winding 14 w-ould of course preponderate, unbalancing the relay 10 in a clockwise direction so as to cause blade 11 to engage contact 18. This would cause the step controller to return to an initial position as will presently be described.

It will now be assumed that there .is an increase in the cooling load and that the temperature in the space I2 rises from '10 to 72 so that the slider 61 is gradually moved downwardly from the upper end of resistance 68 to its lower causes the motor 39 to rotate shaft 46 in a counter-clockwise direction. Upon shaft 46 being thus rotated, cam 41 causes mercury switch 55 ,toppen but relay |05 remains energized through the above described maintaining circuit. When the temperature has risen to 70.5, cam 48 closes mercury switch which completes a circuit for energizing and opening valve I5 and admitting cold water to the coil I3, this circuit being as follows: from line conductor I6I, to 'wire |60, @controller I3I, wire |59, wire |48, contact IIO, switch blade |08, wire |49. wire |55, Wire |56. wire |19, wire |80, mercury switch 60, wire I8|, valve I5, wire |82, wire |52, and wire I5| back to line conductor I 50.

It will be understood of course that as the motor 39 operates in the manner above described. the slider 82 of the rebalancing potentiometer is rotated in a. counter-clockwise direction so as to reduce the amount of resistance in circuit with Thus, it will be seen thatall of resistance 8| is in series with winding 14 and all of resistance 68 is in series with winding 15. The values oi the.

" two resistances are equal and the two windings,

being alike, they are equally energized so as to Vmaintain the mouse-trap relay 10 in balanced position as shown. From the foregoing circuits, it. l

` will be seen that the winding 15 is controlled by the manual switch lcomprising blade |03 and also winding 14 so as to increase its energization to make it equal to thaty of winding 15 so as to rebalance the relay 10, the relay 1u being balanced when the temperature is stable and the step controller 38 assuming a position corresponding to' the controller 65.

Upon a continued rise in temperature, cam 49 will next close mercury switch 6| which will energize relay |22 through the following circuit: from line conductor |6| through wire I 60, con-v troller I I, wire |59, wire |48, contact ||0, switch blade I 8, wire |49, wire |55, wire |56, wire |19, wire |85, wire |86, mercury switch 6|, wire- |81, wiret |88, wire I89,'winding |23, wire |90, Wire |9I, wire |92, and wire |5| back to line conductor |50. At .the same time as relay |22 is energized, a circuit is completed for the solenoid valve 28 as follows: from line conductor |6| through wire |60, controller |3I, wire |59, wire |48, contact ||0, switch blade |08, wire |49, wire |55, wire |56, wire |19, wire |85, wire |86, mercury switch 6|, wire |81, wire |93, valve 28, wire |94, wire |9I, wire |92, and wire I5I back to line conductor |50. When relay |22 is energized, blade |24 moves into engagement with contact |25 completing acircuit for energizing relay I|5 as follows: 'from line conductor I6I, to wire |60. controller |3|,wire |59, wire |48, contact IIO, switch blade |08, wire |49, wire |55, wire |56. wire |19, wire |85, wire |86, mercury switch 6|, wire |81, wire |88, wire |95, contact |25, switch blade |20, wire |96, winding-IIS, wire |91, wire |92, and wire I! back to line conductor |50;

When relay II5 is energized, blades II'! and IIB move into engagement with their respective contacts, engagement of blade I|1'with contact IIS completing a maintaining circuit for winding ||6 as follows: from line conductor |6|, through wire |60, controller |3|, wire |59, wire |46, contact IID, blade |08, wire |09, wire |55, wire |90, wire |99, contact |I9, blade II1, wire 200, mercury switch MII (which will be closed at the time due to relatively high suction pressure), wire winding `I I6, wire |91, wire |92, and wire I5I back to line conductor |50. Engagement of blade' I,|8 with contact |20 .completes a Acircuit for starter |26 as follows: from line conductor |6I, through wire |60, controller |3|, wire |59, wire |48, contact IIO, blade |08, wire |49, wire |55, Wire |98, Wire 202, contact |20, bladeIIB, wire 203, winding |26, and wire 204 back to line conductor |50. When starter |26 is energized, a circuit is completed lor the motor of compressor I9 las follows: from line conductor I6I, through wire 205, the motor of compressor 9, wire 206, contact |29, blade |28,V

wire 201 back to line conductor |50. f

From the foregoing, it is to be seen that clokback to 70.

assente cuit with winding 15. Under these circumstances, the finger 85 will have been rotated to' a position wherein` the limit switch 86 is open.

' With all the compressors in operation, the refrigerative capacity is such that the temperature will now in all likelihood fall and as it falls, the slider 61 is moved upwardly along resistance 60 so as to now decrease the amount of resistance in circuit with winding 14 so as to increase the energization of this winding so that it preponderates over that of winding 15. Thus relay 10 is unbalanced in a clockwise direction bringing blade l1 into engagement with contact 18 and completing a circuit for motor winding 43 as follows: from secondary |00through wire |62, wire |15, blade 11, contact 18, wire 225,A limit switch 81, wire 226, winding 03, wire |18, and wire` |61 back to secondary |00. Motor 39 will now operate to notate shaft 46 in a clockwise direction and the mercury switches will be opened in sequence from right to left as the temperature falls As the temperature falls, starter |26b will first be deenergzed stopping lcompressor 2|, and'starter |26a will thenbe deenergized stopping compressor 20. Similarly, opening of mercury switch 6I will deenergize relay |22 and will deenergize the solenoid valve 28. However,

sure of mercury switch 6| causes opening of solenoid valve 28 and starting of compressor i9 so that the refrigeration system operates with refrigerantbeing supplied by a single compressor. It is to be noted also that power for the -starter |26 for compressor I9 is supplied through the power failure relay |05 and relay I|5 after this relay becomes energized, that is, the power supply for starter |26 is not dependent upon the step controllerv 38.

If the temperature continues to rise, cam 50 'will close mercury switch 62 completingv a circuit for starter |26a as follows: from line ccnductor I6I through Iwire |60, wire'.|59, wire |48, contact |I0,;blade |08, Wire |09, wire |55, wire |561, wire |19, wire |85, wire 2|0, wire 2|I, mercury switch 62, wire 2| 2, winding |210, and wire 2I3 back to line conductor |50. When starter |26a is energized, blade I28a moves into engagement-with contact I29a completing a circuit for the motor of compressor 20 as follows: from line conductor |6| through wire 2I4, the motor of compressor 20, wire 2I5, contact |2911, blade I28a, and wire 2I6 back to line conductor |50.

4If the load is such that even after compressor 20 is started the temperature continues to rise, slider 61 will eventually be moved to the bottom of resistance 68, and at this time mercury switch 63v will -be closed, closure of this switch completing a circuit for starter |2619 as follows: vfrom line conductor |6I, Wire |60, controller |3|, wire |59, wire |48, contact ||0, blade |08, Wire |49, Wire |55, Wire |56, wire |19, Wire |05, wire 'M0` wire 2I1, switch63, wire 2I8, winding |2112, wire 2|9 back to line conductor A-|50. When starter |26b is energized, blade. |285 engages contact' |29b and a circuit for the motor of compressor 2| is completed asA follows:l from lineconductor ||SIl to the motor of compressor 2|, through wire 220, contact I29b, blade I28b, to line conductor |50.

As pointed out, when all the mercury switches have been closed, slider 61 is at the bottom of the resistances, 'and at this time the slider 82 of `the rebalancing :potentiometer 'will be at the counter-clockwise end of resistance 8| and thus all of resistance will' be in'circuit with winding 14 and-all of resistance 8| will no'w be in cirrelay I I5 will remain energized through its maintaining crcuit and .will maintain the starter |26 of'compressor I9 in 4energized position.

AWhen solenoid valve 28 is closed, no more refrigerant will be admitted -to the evaporator, and

with the compressor I9 still in operation the pressure in' the evaporator ywill be pumped down relatively quickly to the value at which controller |36 opens its switch. When mercury switch EHI opens, the maintaining circuit forrelay II5 is interrupted deenergizing this relay and Acausing deenergization of starter |26 and stoppage of compressor |8.

From the foregoing, it isA to Ibe seen that start.- ing of compressor I9 is controlled by the step controller but that this compressor does not stop I until ,the pressure in the evaporator has been pumped down.

If at any time during operation there is a fail 'ure of power supply, for instance, a momentary power failure, the power failure relay |05 will of course lbe deenergized as will all the other` relays.. The step controller may perhaps -be in an intermediate position at this time with mercury switch 55 open, and when the powerv comes back on the power failure relay |05 will not be immediately reenergized because mercury switch 55 is open and the maintaining circuit has been interrupted. When relay |05 is deenergized upon the power failure, blade |01 disengages from contact |09 interrupting the circuit of winding 15 -of relay 10. Thus, when the power supply' is resumed the energization of winding 14 will preponderate over that of'winding 15 which is com; fpletely deenergized and the step controller will recycle, that is, motor 39 will rotate shaft 46- in a'clockwise-direction and it will return toinitial position wherein mercury switch 55 is closed 4and the power failure relay |05 will be reenerglzed through the circuit above described extending through mercury switch 55. When relay |55 has been deenergized as a result of a rpower failure, upon the powerbeing resumed, power will not immediately be supplied to relay I I5 because blade |06 will be disengaged from contact |I0.

Therefore, the relay |05 provides power failure ,protection for the first compressor I8 as well as for the other compressors which are dependent entirely upon the step controller for power supply. By reason of the power failure protection arrangement, upon a failure of power supply, the control mechanism will recycle when power returns and the sequence will be started over again, the mechanism. of course assuming a position dependent upon the position of the controller 65 at the time.

If it is desired to shut down the system manually, the manual switch blade |03 may be disengaged from contact |04 which will entirely interrupt the circuit of windingV so. that the `energization of winding 14 preponderates, un-

balancing the relay 10 in a clockwise direction and causing motor 39 to operate in a direction to return the step controller to initial position. By

` thus'shutting down the system manually in this manner, the power supplyl controlled by the power failure relay |05 is not out olf and thus relay 5 will remain energized keeping compressor* I9 in operation until the evaporator is pumped downto the proper pressure. If manual shut down wereaccomplished merely 'by cutting off` the power supply to the entire setup, all of the compressors would' of course be immediately deenergized and [pump-down of the evaporator would not be obtained.

From` the foregoingthose skilled in theart will appreciate that I have provided a novelarrangement whereby a plurality of compressors may be controlled by a, step controller and, while power thermostatris'es to a predetermined value which may be 72 F. for example. Associated with the blade 254 which is constructed so as to serve as an armature is a permanent magnet 256 so disposed as to cause the blade 254 to engage' with and disengage from the contact 255 with a snap action in a manner .Well known in the art. The thermostat 252 may have a differential of 2, for example, that is, opening at a temperature of 70 F.

The thermostat 252 controls a relay 258 cornprising a winding 259 having an armature associated therewith which is connected to a-movable switch blade 260 which is moved-to the left by the armature into engagement with a fixed electrical contact 26| when the winding 259 is energized. l

Power for operation offthe relay 258 and theY valve 246 is supplied by a step down transformer 262 comprising a primary Winding 263 and a secondary winding 264 having a fewer number of turns than the primary. Power is supplied to the primary winding-through wires 265 and 266 which may be connected to any suitable source of power not shown.

The relay 258 controls another relay orstarter 269 comprising a winding 210 having an 'armature associated therewith connected to movable failure protection is provided at all times, one,

compressor will always pump downthe evapo` rator when operation of the rfrigeratlng sys-. tem is not required. Moreover, upon a manual shut down, one of the compressors will pump down the evaporator in the same manner,

L Referring to Figure 2 of the drawings, I have shown another formof 'my invention wherein a.

single compressor is used and wherein the control arrangement provides for starting the compressoronly when there is a demand by the thermostat and causing the compressor evaporator each time that the thermostat becomes satisfied. Referring to Figure 2, numeral 240 designates a compressor driven by an electric motor, the compressor discharging into a conto pump down the,

switch blades 21| .and 212 which are moved to the left by the armature into engagement with fixed electrical contacts 213 and 2,14 respectively wnenthe winding 210 is energized. Power for operation of the relay 269 is supplied by stepdown transformer 216 havingfa'- primary winding 211 and a'secondary winding 2"|8 having a fewer number of turns. Power may be supplied tothe primary winding 211 through wires 2-19 and 280 which may be connected to the above referred to power source. Oneof the switches operated by relay 269 controls the motor of compressor 240 as will presently be described .and the other controls a maintaining circuit for the winding 210 which maintaining circuit is controlled by a suction pressure controller designated by the numeral 282` The controller 282 comprises an .expansible and contractible bellows 283, the interior ofwhich is connected to the pipe 245 by a tube 284 so that the bellows expands and contracts in accordance denser 24| through a, pipe 242. The condenser is i connected to an evaporator 243 by a pipe 244 and the outlet of the evaporator is connected to thesuctioninlet of the compressor by a pipe 245.

Disposed in the pipe 244 is a solenoid type stop valve 246, and also interposed in the pipe 244is a thermost'atic expansion valve 241. The valve 241 is of the Ausual type -adapted to maintain predetermined degree of superheat. at the outlet of the evaporator. 'I'he valve 241 includes an expansible operating chamber whichis connected to a thermal bulb 248 by a capillarygtube 249, the

. bulb 248 containing avaporizable liquid and be ing disposed in intimate heatlexchange relation- -ship with the pipe 245. The liquid in the bulb 248 vaporizes and develops a pressure for actuating the valve depending upon the temperature in the pipe 245. The operation of this type of valve is well known in the art. 1 f

The'compressor motor is controlled primarily by a thermostat 252 responsive to the temperature of a medium, for instance, air being cooled by the `evaporator 243. The thermostat 252 com- Y prises a. bimetal element 253 arranged to actuate a movable switch blade 254 which is moved to the left into engagement with a xed electrical contact 2 55 when the temperature aiectlng the 75 movable end of the bellows 283 carries an operating stem into engagement with which a pivoted switch carrying lever 285 isnormally urged by a coil spring 286. The lever 285 carries a mercury switch 281 having electrodes at its left end which are engaged when the suction pressure is at or above a predetermined. relatively highlyalue, at which' the bellows 283 i's expanded, with the lever 285 in a position such as that shown in the drawings. When the suction pressure falls to apredetermined relatively low value, the bellows 283 contracts moving lever 285 in a clockwise direction and opening a switch 281'.

In operation, when the temperature affecting -thermostat 252 rises to the predetermined value of 72 F., for example, blade 254 engages contact 255v completing a circuit for energizing and opening solenoid valve 246 and completing another circuit for the relay 258, the circuit for the valve 246 being as follows: from the secondary 264 of transformer 262 through wire 289 to valve 246,

' pre ergized, a circuit .is completed for relay 269 as follows: from secondary 218 of transformer 216, through wire 299, switch 261, wire 300, wire 295, switch blade 260, contact 26l, wire 296, wire 291, winding 210, wire 298 back to secondary 218. Completion of this circuit energizesthe relay 269 moving switch blades 21| and 212 into engagement with their respective contacts, energizing the motor of compressor 240 and completing a maintaining circuit for relay 269. The maintaining circuit for relay 269 is as follows: from secondary 218 through -wire 299, mercury switch 281, (which will normally be closed at the time) wire 300, wire 306, switch blade 212, contact 216, wire 30|, wire 291, winding 210, and wire 298 back to secondary 218. The circuit for the motor of compressor 240 is as follows: from wire 219 to wire 302, switch blade 21|, contact 213, wire 303, the motor of compressor 240, wire 304 back to wire 280, the wires 219 and 280 being connected to a suitable source of power as pointed out above.

. Upon completion of the circuits described, the soleigoid valve 246 will be opened and the comor 240 will operate to produce refrigeration in the evaporator 243. By reason of the maintaining circuit for relay 269, the compressor motor will remain energized until the suction pressure falls to a low enough value to cause the mercury switch 281 to open, that is, the compressor will remain in operation until mercury switch 281 opens, even though the temperature of the air falls to a low enough value to cause thermostat 252 tol open its contacts. When the. thermostat 252 has opened its contacts and the suction presusure has fallen to a low enough value to openmercury switch 281, relay 269 will be deenergized and the compressor will be stopped. Of course, after the thermostat 252 has opened its contacts, .the solenoid valve 246 will be closed cutting oil the supply of refrigerant tothe evaporator, and thereafter the compressor will pump the evaporator down to the settingr of controller 282 relatively quickly. .If during the time that the thermostat 252 is-satisfled, the pressure in the evaporator should rise to thesetting of controller 282 due to leakage past the valve 246 or the like. the compressor motor will not be energized because the controller 282 controls only the maintaining circuit of relay.269 and is not operable to energize this relay but only to deenergize it after the relay 258 has been deene'rgized. Thus, when the thermostat 252 becomessatised, the evaporator is always pumped down and thereafter the compressor is maintained inoperative until the thermostat 252 again calls for operation of the compressor. Thus, the system provides for pumping'down of the evaporator and positive disconnection of` the compressor motor until there is another demand for the refrigera- `tion. i

disclosed are representative of its' preferred forms, it lbeing understood that various modifications and variationsin the invention will occur to those skilled in the art. be interpreted-in an illustrative rather than a limiting sense, and the invention -is to be limited only in accordance with the claims appended hereto. v

I claim as my invention: I

1. In apparatus of the character described, in combination, a plurality of electrical devices to be controlled, an electrical control device having My disclosure is 'to' ,position for sequentially controlling-said first devices,.control means for normally controlling said control device, said means being so arranged that upon failure of power supply said means assumes a position wherein said control device assumes its initial position upon resumption of the power supply, and separate means for automatically controlling one of said rst devices. said/ last means being controlled by said aforementioned means. 3. A refrigeration system comprising, in combination, a refrigerant translating device, an

evaporator, means responsive to a condition of treated air, rst relay means controlled by said 'condition responsive means. second relay means controlled by said rst relay means and arranged to control said compressor, means forming a maintaining circuit for said second relay means for keeping it in a position causing operation of the translating device, and means responsive to evaporator pressure controlling said maintaining circuit arranged to interrupt said circuit at a predetermined evaporator pressure.

4. A refrigeration system comprising, in cdmbination, a plurality of refrigerant translating devices, an evaporator, a step controller controlling said devices, means responsive to a condition oi treated air controlling said step controller, and

- control means for maintaining one translating de- The embodiments of my invention which I have -v vice in operation after it would otherwise be shut down by the step controller until a predeltermined evaporator pressure is reached.

5. In a refrigeration system, a plurality of refrigerant translating devices, an evaporator,

a step controller controlling said devices, means 4 responsive to a condition of treated air controlling said'step controller, and control means for maintaining one translating device in operation after it would otherwise be shut down by the step controller until a predetermined evaporator pressure is reached, said control means comprising a relay controlling said one translating device, circuit means whereby said relay is energizable by the stepv controller for starting said one translating device, means forming a maintaining circuit for said relay, and a device responsive to evaporator pressure controlling the maintaining circuit.

6. In a refrigeration system, a` plurality oi' refrigerant translating devices, an evaporator, a step controller controlling the devices, normally energized'relay means controlling the power supply to the step controller, means including a device responsive to suction pressure controlling one translating device to cause it to pump down the evaporator after the step controller has assumed .relay is :de-energized upon a power failure, upon the return of power, the step controller will operate to initial position.

7. A refrigeration system comprising,.ln combination, a plurality of refrigerant translating devices; an evaporator; a step controller controlling said devices, said step controller having a plurality of positions including an initial posi-1 tion; means comprising a normally energized re.. lay vcontrolling the supply of power to the Step .controller and translating devices, said relay and step controller being so related that the step controller must be in initiall position to initially energize the relay; co-ntrol means including a suction pressure responsive device so arranged that one device, after having been put in operation by the step controllen'remains in operation until the eyapo'rator is pumped down to a predetermined pressure even though the step controller moves to a position not demanding operationof any of the translating devices, and'means as- .sociatcd with said relay and so related to said step controllerthat if the relay is deenergized as a result of a ,power failure, upon resumption of the power supply the step Lcontroller will return to initial position thereupon re-energizing the relay. 8. A refrigeration system comprising, in combination, a plurality of refrigerant translating devices; an evaporator; a step controller controlling said devices, said step controller having a plurality of positions including an initial position; means comprising anormally energized relay controlling the supplyof power to the step controller and translating devices, said relay and step controller being so related that the step controller must be in initial position to initially energize the relay; a second relay energizable by said step controller for starting one translating device, means forming a maintaining circuit for said second relay whereby said one device is kept in operation to pump down lthe evaporator after the step controller moves to a position not demanding operation of vany of the translating devices; means responsive to evaporator pressure arranged to interrupt said maintaining circuit at a predetermined pressure; means associated with said .first relay and so related to said step controller that if the first relay is de-energized as a resu-lt of a power failure, upon resumption of the power supply the stepcontroller will return to initial position thereupon re-energizing the ilrst relay, and means wherebysaid first relay controls said maintaining circuit so that after a power failure said second relay' cannot be reenergized until the step controller returns to initial position.

9.v A refrigeration system comprising, in combination, a refrigerant translating device, -an evaporator, means controlling the device comprising a relay and a control instrument respon- .sive to a condition of medium treated by the evaporator, means forming a maintaining circuit for the relay, and means 'responsive to evaporator pressure controlling the maintaining circuit to cause the translating device to pump down the evaporator after the demandsof the control in...1

strument have been satisiied.

l0. A refrigeration system comprising, in com-"- translating devices, an evaporator, a step 'controller controlling said devices, means responsive to a condition of treated aircontrolling said step controller, and control means for maintaining one translating device in operation after it would otherwise be shut down by the step controller until a predetermined evaporator pressure is reached, said control means comprising a relay controlling said one translating device, circuit means whereby said relay is energizable by the step controller for starting said one translating device, means forming a maintaining circuit for said relay, a device responsive to evaporator pres` sure controlling the maintaining circuit, and manual shut-down means whereby upon a manual shut down`the step controller moves to a position interrupting the initialgenergizing circuit of the relay, but the relay remaining energized through its maintaining circuit until the said /predetermined evaporator f pressure reached.

12. In al refrigeration .system comprising an evaporator and a plurality of compressors for feeding liquid refrigerant thereto, in combination; valve means controlling the supply of refrigerant to said evaporator;- means responsive to the demand for refrigeration; means controlled thereby for opening said valve means and energizing a rst of said compressors when said demand is relatively small; means controlled by said responsive means :for successively energizing the other of said compressors as said demand increases, said responsive means'acting` through said controlled means to successively deenergize bination, a plurality of refrigerant translating:

y devices, an evaporator, a step controller for se-l quentially starting the translatingdevices, means controlling one translating device for causing it to pump the evaporator down to a predetermined pressure when the system is shut down, and manual means for shutting down the,..-system, said last means being so related to the step controller that upon a manual shut-down the step controlthe other of said compressors and iinally close said valve means as said. demand becomes satised, and means responsive to evaporator pressure for maintaining said 'rst compressor energized until said pressure decreases to a predetermined value.

`13. In a refrigeration system comprising an evaporator and a plurality of compressors `for feeding liquid refrigerant thereto; in combination, valve means controlling the supply of refrigerant to said evaporator; means responsive to the demand for refrigeration; means controlled .thereby -for opening saidvalve means and energizing a rst of said compressors when said demand is relatively small; means controlled by said responsive means for successively energizing the other ofsaid compressors as said demand increases, and means responsive to a power failure and operative upon a resumption of power to cause said controlled means to return to the position which they would normally occupy when thereis no demand for refrigerant, and thereafter energize said compressors successively to supply sufficient refrigerant to meet the demand for refrigeration.

14. In a refrigeration system comprising an .evaporator and a plurality of compressors 'for feeding liquid refrigerant thereto; in combination, valve means controlling the supply of refrigerant to said evaporator; means responsive to the demand for refrigeration; means controlled thereby for opening said .valve means and energizing a first of said compressors when said demand is relatively small; means controlled by said responsive means for successively energizing the other qt said compressors as said `demand increases, said responsive'means acting through saidcoritrolled means to successively deenergize assessetion pressure arranged to cause continued operposition which they Would normally occupy when A there is no demand for refrigerant, and thereafter energize said compressors successively to supply sufiicient refrigerant to meet the demand for refrigeration.

15. In a refrigerating system comprising, in combination, a refrigerant translating device, a

condenser, evaporator means, said translating device, when operating, causing refrigerant flow through said condenser to said evaporator means, suction means connecting the outlet of said evaporator means to the inlet of vsaid translating device, means responsive'to a condition or a medium being treated by said evaporator means for starting the translating device, talvel means controlling the flow of refrigerant from said condenser` to said evaporator means, said valve means being capable of stopping all fiow from said condenser, said condition responsive means being arranged to control said valve means to stop all refrigerant flow from said condenser upon the condition responsive means becoming satisfied, and means responsive to sucation of the translating device after said condition `responsive means is satisfied until a predetermined suction pressure is reached.

I 16. A refrigerating system comprising, in combination, a refrigerant translating device, a relay controlling .said device, a condenser, evaporator means, operation of said translating device causing refrigerant flow through said condenser to said evaporator means, suction means connecting the outlet of said evaporator means to the inlet of said translating device, means responsive toa condition of a medium being treated for actuating said r'elay and starting the translating device, valve means controlling the flovt of reirigerant from said condenser to said evaporator means, said valve means being capable of stopping all flow from said condenser, said condition responsive means being arranged to control said valve means to stop all refrigerant flow from said condenser upon the condition responsive means becoming satisfied, means forming a maintaining circuit for said relay, and means responsive to suction pressure controlling said maintaining circuit and so arranged that said translating device is kept in operation by reason of said maintaining circuit after the condition.re sponsivev means is satisfied until a predetermined relatively low suction pressure is reached.

WILLIAM L. MCGRA'I'H.

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