US2251891A

US2251891A - Refrigeration control system

Info

Publication number: US2251891A
Application number: US228508A
Authority: US
Inventors: Alwin B Newton
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1938-09-06
Filing date: 1938-09-06
Publication date: 1941-08-05
Anticipated expiration: 1958-08-05

Description

Aug.` 5, 1941 A. B; NEWTON 2,251,891

RFRIGERATION CONTROL SYSTEM Filed Sept. 6, 1938 f f l nomtor attorney Patented Aug. 5, 1941 REFRIGERATION CONTROL SYSTEM Alwin B. Newton, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.,V a corporation of Delaware Application September 6, 1938, Serial No. 228,508-

19 Claims.

This invention relates to control systems in general and more particularly to control systemsfor controlling the operation of a refrigerating apparatus.

An object of this invention is to provide a novel control arrangement for an electrically operated device wherein a plurality of control switches control individually the operation of a plurality of relays and wherein the electrically operated device can be operated only when all of the relays are pulled in.

A further object of this invention is to utilize this control arrangement for controlling the operation of a compressor of a refrigerating apparatus wherein the control switches are operated in accordance with refrigerating conditions,

` such as pressure on the high pressure side of the refrigerating apparatus, evaporator temperature,

compressor overload conditions and the temperature of the medium being cooled by the refrigerating apparatus. With such a control arrangement, it is possible to require the pressure on the high pressure side to reduce to a predetermined low value and the evaporator temperature to rise to a defrosting value before the compressor can be placed in operation upon a call for cooling by the medium temperature responsive switch. 'Ihis insures defrosting of the evaporator during each cycle of operation and prevents the starting of the compressor against high head pressures.

Other objects and advantages will become apparent to those skilled in the art upon reference, to the accompanying specification, claims and drawing.

The single sheet of drawings illustrates the preferred form of this invention.

Referring now to the drawing, an enclosure containing a medium to be cooled is designated at I0. For purposes of illustration, this enclosure is shown as being a storage chamber such as a walk-in box. The storage chamber is cooled by an evaporator I I suitably connected to a refrigerating apparatus generally designated at I2, which may comprise a compressor I3 operated by a compressor motor I 4. Refrigerant is delivered from th-e compressor I3 through a high pressure line I5 to a condenser I6 and the condensed refrigerant is collected in a receiver I1. Condensed refrigerant ows from the receiver I1 through an expansion valve I8 into the evaporator I I wherein it is evaporated and performs cooling functions. Evaporated refrigerant is drawn from the evaporator II through a suction line I9 by the compr-essor I3. The expansion valve I8 may be of the thermostatic type having a bulb 20 lochamber 28.

cated at the discharge side of the evaporator II connected by a capillary tube 2l to the expansion valve I8. Since such a construction is old in the art, a further description thereof is not considered necessary.

The compressor motor I4 and hence the refrigerating apparatus is illustrated as being controlled by three controllers. A controller responsive to the condition of the medium being cooled is generally designated at 23 and this controller may take the form of a temperature responsive controller responsive to the temperature of the air within the enclosure I0. A controller responsive to the pressure on the high pressure side of the refrigerating apparatus is generally designated at 24. A controller responsive toa condition indicative of evaporator temperature is generally designated at 25 and may take the form of a pressure responsive controller responsive to the pressure on the low pressure side of the refrigerating apparatus. Inasmuch'as suction pressure and evaporator temperature are proportional, the suction pressure controller 25 inresponding to variations in suction pressure also responds to the temperature of thel evaporator means Il.

The temperature responsive controller 23 may comprise a casing 21 to which is secured a bellows The bellows chamber 28 is connected by a capillary tube 29 to a bulb 3U located within the enclosure I0. The bellows chamber 28 andbulb 30 are charged with a volatile iluid so that a plunger 3I is operated in accordenclosure I0.

ance with variations in temperature within the The plunger 3l operates a lever 32 pivoted on a fulcrum 33 against the action of an adjustable tension spring 34. Upon an increase in temperature, the lever 32 is rotated in a clockwise direction, and upon a vdecrease in temperature the spring 34 rotates the lever 32 in a counter-clockwise direction. A bracket 36 carries resilient arms 31 and 38, the arms being urged toward the lever 32 by their own resiliency. The arm 31 abuts against the lever 32, and the arm 38 abuts against a lever 39 pivoted at 40 and adjustably positioned by a screw 4I.

Contacts

42 and 43 are carried by the arms 31 and 38, respectively, and upon an increase in temperature the lever 32 moves the contact 42 into engagement with the contact 43. The arm 38 also carries a -contact 44 which is adapted to engage an adjustable contact 45 carried by a post 46. After the

contacts

42 and 43 have been engaged and a further temperature rise occurs, the

Contact 44 is moved into engagement with the contact 45. For purposes of illustration, it is assumed that upon a rise in temperature contact 42 first engages contact 43 at 40 and then contact 44 engages contact 45 at 42. Upon a decrease in temperature, contact 44 iirst disengages contact 45 at 42;and then contact 42 disengages contact 43 at 40.

The temperature responsive controller 23 also includes a relay having an operating coil 48 for vmay comprise a casing 68 to which is secured a bellows chamber 6| connected by a pipe 62 to the high pressure line l 0i' the refrigerating apparatus. The operating parts within the casing 68 are the same as the operating parts within the casing 2i' of the temperature responsive controller 23 with one exception, and accordingly, like reference characters primed have been utilized for these parts. The location of the spring 3ft' and the plunger 3|' of the pressure responsive controller 24 is just the opposite of the location of the plunger 3| and spring 34 of the temperature responsive controller 23. Accordingly, upon an increase in high pressure the lever 38' is rotated in a counter-clockwise direction, while upon a decrease in high pressure the lever 32' is rotate/d in a clockwise direction. For purposes of illustration, it is assumed that upon a decrease in high pressure Contact 42 first engages contact 43' at 185 pounds and then contact 44' engages contact 45' at 140 pounds. Upon an increase in high pressure, contact 44' first disengages from contact 45' at 140 pounds and then contact 42"disengages contact 43' at 185 pounds.

The low pressure controller 25 may comprise a casing 65 to which is secured a bellows charnber 66 which, in turn, is connected by a pipe 81 to the low pressure or suction line |9 of the refrigerating apparatus. The operating parts contained within the casing 65 are exactly the same as the operating parts contained within the casing 2i of the temperature responsive controller 23 and therefore like reference characters double primed have been utilized for like parts. For purposes oi' illustration, it is assumed that upon an increase in suction pressure the contacts 42" and 43" engage at 20 pounds and then contacts 48" and 45" engage at 35 pounds. Upon a decrease -in suction pressure, contacts 44" and 45" separate at 35 pounds and then contacts 42" and 43" separate at 20 pounds. It is also assumed that the suction pressure value of 35 pounds at which contacts 44" and 45" engage represents a temperature above the defrosting temperature of the evaporator il so that the contacts 44" and 45" only engage after the evaporator means has defrosted.

An overload cut-out switching mechanism may be utilized with the control apparatus of this invention, and this overload cut-out switching mechanism is generally designated at 10. I may comprise arms 1i and 12 carrying contac s 13. The arm 'H is so arranged that it tends to separate thecontacts 13 by its own resiliency. The arm 'H may be held into contact making position by means of a bimetallic element 14 suitably mounted on a bracket 15. The bimetallc e19- ment 14 is influenced by a heater 16 located in the compressor load'circuit. Upon the occurrence of an overload condition in the compressor load circuit, the bimetallic element 14 is exed upwardly to allow the arm 1| to separate the contacts 13, whereupon the circuit through the contacts 13 is broken. A manual operator 11 may be utilized for reclosing the contacts 13 sov that they may be held in engagement by the bimetallic element 14 after the same has cooled down following the occurrence of an overload condition. Power is supplied to the compressor motor I4 and to the control system by means of line wires 89 and 8| leading from some source of power, not shown.

Assume now that the temperature within the enclosure I0 has risen to 40 to cause

contacts

42 and 43 and contacts 44 and 45 to be closed. A circuit is thereupon completed from the line ,wire through arm 1|, contacts 13, arm 12,

a maintaining circuit for the operating coil 48 which is independent of the contacts 44 and 45 and this circuit may be traced from the overload cut-out 1|! through

wires

82, 84, 84, and 85, post 46, Wire 88, contact V53, switch arm 50, contact 54, wire 89, arm 38,

contacts

43 and 42, arm 31, wire 86, operating coil 48, and wire 81 back to the line wire 8|. Completion of this circuit maintains the operating coil 48 energized until such time as the

contacts

42 and 43 separate.

When' the high pressure decreases to 140 pounds, contacts 42' and 43' and contacts 44' and 45 are in engagement to complete a circuit from the overload cut-out 18 through

wires

82, 83, and 9|, contacts 45 and 44', arm 38', contacts 43' and 42', arm 31', wire 92, operating coil 48', wire 93, contact 5|, switch arm 49, contact 52, and Wire 81 back to the line wire 8|. Completion of this circuit energizes the operating coil 48' when the high pressure decreases to 140 pounds providing the relay of the temperature lresponsive controller 23 is pulled in.

Energization oi the operating coil 48' moves the switch arms 49 and 53 into engagement with their respective contacts. Movement of the switch arm 58' into engagement with the contacts 53'jand 54 completes a maintaining circuit for the operating coil 48' which is independent of the contacts 44' and 45'. This circuit may be traced from the overload cut-out 10 through

Wires

82, 83, and 9|, post 46', Wire 94, contact 53', switch arm 50', contact 54', wire 95, arm 38', contacts 43' ande42', arm 31', wire 92, operating coil 48', Wire 93, contact 5|, switch arm 49, contact 52, and wire 81 back to the other lin'e wire 8|. Completion of this circuit maintains the operating coil 48' energized until the high pressure increases to pounds to separate the contacts 42 and 43', or until the relay of the temperature responsive controller 23 drops out.

When the suction pressure rises to 35 pounds, the contacts 44" and 45" and the contacts 42" and 43" are moved into engagement. This completes a starting circuit for the operating coil 48" which may be traced from the overload cut-out 10 through

wires

82V, 83, 84, and 91, contacts 45" and 44", arm 38", contacts 43" and 42", arm 31", wire 98, operating coil 48", wire 99, contact I', switch arm 49', contact 52',

kwire 93, contact 5|, switch arm 49, contact 52,

and wire 81 back to the line wire 8|. Completion of this circuit energizes the operating coil 48" to move the switch arms 49" and 50 into engagement with their respective contacts. Movement of the switch arm 50" into engagement with the contacts 53" and 54" completes a maintaining circuit for the operating coil 48" which is independent of the contacts 44" and 45". 'Ihis circuit may be traced from the overload cut-out through

wires

82, 83, 84, and 91, post 46", wire |00, contact 53", switch arm 50, contact 54", Wire |0|, arm 38", contacts 43" and 42", arm 31", wire 98, operating coil 48", Wire 99, contact 5|', switch arm 49', contact 52', wire 93, contact 5|, switch arm 49, contact 52', and wire 81 back to the other line wire 8|. Completiony of this circuit maintains the operating coil 48" energized until the suction pressure decreases to pounds to separate the contacts 42" and 43", or until the relay of the temperature responsive controller 23 drops out or until the relay of the high pressure responsive controller 24 drops out.

When all of the relays of the temperature responsive controller 23, the high pressure responsive controller 24, and the suction pressure responsive controller 25 are pulled ins a circuit for the compressor is completed which may be traced from the line wire 80 through the overload cut-out 10, wires 82 and |05, heater element 15, wire |06, compressor motor I4, wire |01, contact 5i, switch arm 49", contact 52", wire 99, contact 5|', switch arm 49', contact 52', wire 93, contact 5|, switch arm 49, contact 52, and wire 81 back to the other line wire 8|. Accordingly, it is seen that the load switches of the relays of the three controllers are connected in series with the compressor motor |4 so that the compressor motor |4 can be operated only when all three relays are pulled in.

When the temperature of the enclosure rises to 42, when the high pressure decreases to 140 pounds, and the suction pressure increases to pounds, all of the relays are pulled in to complete the compressor motor circuit and place the reirigerating apparatus in operation. If the suction pressure should decrease to 20 pounds, the relay of the suction pressure responsive controller 25 drops out to stop operation of the refrigerating apparatus, the relays of the temperature responsive controller 23 and the high pressure responsive controller still remaining in. The relay of the suction pressure responsive controller cannot again be pulled in until the suction pres- Sure rises to 35 pounds and accordingly defrosting of the evaporator il must occur before the refrigeratng apparatus can be placed in opera- Cil temperature responsive controller 23 will then drop out. In addition to interrupting the load circuit to the compressor motor |'4, dropping out of the relay of the temperature responsive controller 23 also drops out the relays of the high pressure responsive controller 24 and the suction pressure responsive controller 25 so that the refrigerating apparatus cannot again be placed in operation until the temperature within the enclosure |0 rises to 42, the vhigh pressure kdecreases to 140 pounds, and the evaporator is defrosted.

If an overload condition in the compressor motor circuit occurs, the overload cut-out 10 trips open and all of the relays are dropped out. Hence following an overload condition the compressor cannot be restarted even though the overload cut-out is reset until the temperature within the enclosure |0 increases to 42, the high pressure decreases to 140 pounds and the suction H,pressure increases to 35 pounds. -Upon a moi mentary power failure condition the same sequence of operation is required to place the refrigerating apparatus back into operation.

Summing up, 'if after the refrigerating apparatus has been" placed in operation it is stopped by the occurrence of a low suction pressure, the refrigerating apparatus cannot be replaced in operation until the evaporator has defrosted. If the refrigerating apparatus has been stopped upon the occurrence of a high head pressure, it cannot be restarted until the head pressure decreases to a low value and the evaporator has defrosted. If the refrlgerating apparatus has b een stopped upon the occurrence of a low temperature condition within the enclosure l0, or if it is stopped upon the occurrence of an overload condition in the compressor motor circuit, it cannot be restarted until the temperature within the enclosure rises to a predetermined value, the high pressure decreases to a predetermined value7 and the evaporator has defrosted. Accordingly, this system insures that the evaporator |I is defrosted before the refrigerating apparatus is placed in operation regardless of how operation of the refrigerating apparatus was stopped.

If it be'desirable to insure that the refrigerating apparatus cannot be placed in operation until the pressure on the high pressure side of the rerigerating apparatus has decreased to a predetermined low value regardless of how the refrigerating apparatus was stopped, the location of the suction pressure responsive controller 25 and the high pressure responsive controller 24 in the circuit may be reversed. With such a revised arrangement the refrigerating apparatus could not be started under any conditions until the pressure on the high pressure side of the refrigerating apparatus decreased to, illustratively, pounds. Likewise, if it be desirable to prevent restarting of the refrigerating apparatus until the temperature within the enclosure |0 increasesto 42 regardless of how the refrigerating apparatus was stopped, the temperature responsive controller 23 and the suction pressure responsive controller may be reversed in the circuit. With such an arrangement, it would be impossible to restart the refrigerating apparatus until the temperature within the enclosure III increases to 42 regardless of how the refrigeratng apparatus was shut down. Hence this invention contemplates various locations of the various controllers in the circuit arrangement so that any desired sequence of operation may be obtained.

II, as shown, the starting circuit of the operating coil 48' of the high pressure responsive controller passes through the-switch means of the temperature responsive rcontroller 23 and if the starting circuit o! the operating coil 48 oi the suction pressure controller 25 passes through the switch means of the relay of the high pressure responsive controller 2l and the switch means of the -relay of the temperature responsive controller 23, it is not necessary to pass the load circuit of the compressor motor I 4 through the three relays. 'Ihe compressor motor H/could be controlled solely by the switch means of the relay of the suction pressure controller 25 and substantially the same results would be obtained. This is predicated on the fact that the energization of the operating coil 48" of the suction pressure controller 25 is controlled by the switch means of the relays of the temperature responsive controller 23 and the high pressure responsive controller 2l. Such a modied cntrol arrangement is also within the contemplation of this invention.

If the load circuit for the compressor motor i4 passes serially through the switch means ,of all of the relays as illustrated in the drawing, it is not necessary to pass the starting circuit of the relay 48' of the high pressure responsive controller through the switch means of the relay.

of the temperature responsive controller or to pass the starting circuit of the operating coil 48" of the suction pressure controller 25 through the switch means of the relays of the temperature responsive controller 23 and the high pressure responsive controllex- 24. Substantially the same mode of operation would be obtained by this revised arrangement and this revised arrangement is also within the contemplation oi' this invention. y

By passing the load circuit serially through the three relays and by passing the starting circuits of the relays through the other relays as is shown in the drawing, shutting down of the refrigerating apparatus is absolutely assured even though one of the relays should stick to prevent shutting down of the refrigerating apparatus.

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

I claim as my invention:

l. In a control system for an electrically operated device, the combination oi, a nrst switch,

opening the same in the opposite order, second relay means including an operating coil and switch means closed upon energization thereof, circuit connections for completing a circuit through the second switch and the operating coil oi.' the second relay means to energize the same, circuit Vconnections for completing a circuit through the third switch.' the switchv means of the iirst relay means, the switch means of the second relay means and the operating coil of the second relay means to maintain the operating coil of the second relay means energized until the third switch is opened or the operating coll o1' the rst relay means is deenerglzed whereupon the operating coil of the second relay means is deenergized, anda circuit for connecting the switch means of both relay meansl in series with the electrically operated device to operate the electrically operated device only when the operating coils of both relay means are energized.

2. In a control system for an electrically operrelay means including an operating coil and iirst relay means including an operating coil and switch means closed upon energization thereof,

wiring connections lfor completing' a circuit through the second switch, the switch means of the nrst relay means and the operating coil of the second relay means to energize the same when the operating coil of the nrst relay means is energized, wiring connections for completing a circuit through the third switch, the switch means of the ilrst relay means. the switch means of the second relay means and the operating coil of the second relay means to maintain the operating coil of the second relay means energized until the third switch is opened or the operating coil of the rst relay means is deenergized whereupon the operating coil oi' the second relay means is deenergized, and wiring connections for controlling the electrically operated device by the switch means ofthe second relay. means to operate the electrically operated device only when both relay means are energized.

3. In a control system for an electrically operated device, the combination of, iirst and second switches, means for closing the rst and second switches in sequence and for opening the same in theopposite order, rst relay means including an operating coil and switch means closed upon energization thereof, means for completing a circuit through the second switch and the operating coil of the, first relay means to energize the same, means for completing a circuit through the iirst switch, the switch means' oi the iirst relay means and the operating coil of the first relay means to maintain the same energized until the rst switch is opened whereupon the operating coil of the iirst relay means is deenergized, third and fourth switches, means for closing the third and fourth switches in sequen'ce and for opening the same in the opposite order, second relay means including an operating coil and switch means closed upon energization thereof, means for completing a circuit through the fourth switch and the operating coil of the second relay means to energize the same, means for completing a circuit through the third switch, the switch means of the first relay means, the

switch means of the second relay means and the operating 'coil of the second relay means to maintain the same energized until the third switch means is opened or the operating coil of the first relay means is deenergized whereupon the operating coil of the second relay means is deenergized, and means for connecting the switch means of both relay means in series with the electrically operated device to operate the electrically operated device only when the operating coils of both relay means are energized.

4. In a control system for an electrically operated device, the combination of, first and second switches, means for closing the first and second switches in sequence and for opening the same in the opposite order, rst relay means including an operating coil and switch means closed upon energization thereof, means for completing a circuit through the second switch and the operating coil of the first relay means to energize the same, means for completing a circuit through the first switch, the switch means of the first relay means and the operating coil of the first relay means to maintain the same energized until the first switch is opened whereupon the operating coil of the first relay means is deenergized, third and fourth switches, means for closing the third and fourth switches in sequence and for opening the same in the opposite order, second relay means including an operating coil and switch means closed upon energization thereof, means for completing a circuit through the fourth switch, the switch means of the first relay means and the operating coil odfs the second relay means to energize the same when the operating coil of the first relay means is energized, means for completing a circuit through the .third switch, the switch means of the vfirst relay means, the switch means of the second relay means and the operating coil of the second relay means to maintain the same energized until the third switch means is opened or the operating coil of the first relay means is deenergized whereupon the operating coil of the second relay means is deenergized, and means for controlling the electrically operated device by the switch means of the lsecond relay means to operate the electrically operated device only when both relay means are pulled in.

5. In a control system for an electric motor, the combination of, a first switching means having starting, intermediate and stopping positions, first relay means including operating means and switch means operated thereby, circuit connections controlled by the first switching means for initially energizing the operating means of the first relay means to close the switch means thereof when the first switching means moves to its starting position, circuit connections controlled by said first switching means and the switch means of the first relay means to maintain the switch means of the first relay means in closed position when the first switching means moves to its intermediate position and until it moves to its stopping position, second switching means also having starting, intermediate, and stopping positions, second relay means including operating means and switch means operated thereby, circuit connections controlled by the switch means of the first relay and by said second switching means when in its starting position to initially energize the operating means of the second relay means, circuit connections controlled by the switching means of both the first and second relay means and by the second switching means to maintain the switch means of the second relay means closed upon movement of the second switching means to its intermediate position and until it moves to its stopping position, a circuit for the motor controlled by the switch means of the second relay means, and an overload cutout mechanism responsive to overload conditions on the motor and including a vswitch in circuit with the operating means of each of said relay means whereby upon opening of said switch both the first and second switching means must return to their starting positions before their associated relay means can again be energized.

6. In a refrigeration system including a refrigeration apparatus having a compressor and evaporator means, the combination with said apparatus of, a first switching means having starting, intermediate and stopping positions, first relay means including operating means and switch means operated thereby, circuit connections controlled by the first switching means for initially energizing the operating means of the first relay means to close the switch means thereof when the first switching means moves to its starting position, circuit connectionscontrolled by said rirst switching means and the switch means of the first relay means to maintain the switch means of the first relay means in closed position when the first switching means moves to itsintermediate position and until it moves to its stopping position, second switching means also having starting, intermediate and stopping positions, second-relay means including operating means and switch means operated thereby, circuit connections controlled by the switch means of the first relay and by said second switching means when in its starting position to initially energize the operating means of the second relay means, circuit connections controlled by the switching means of both the first and second relay means and by the second switching means to maintain the switch means of the second relay means closed upon movement of the second switching means to its intermediate position and until it moves to its stopping position, a circuit for the compressor controlled by the switching means of the second relay means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for operating one of the switching means, means responsive to a condition which is a measure of evaporator temperature for operating the other of the switching means, and an overload cutout mechanism responsive to overload conditions of `the compressor and including a switch in circuit with the operating means of each of said relay means whereby upon opening of said switch both the first and second switching means must return to their starting positions before their associatedrelay means can again be energized.

7. In a control system for an electrically operated device, the combination of, first switching means, first relay means including operating means and switch means operated thereby, circuit connections controlled by the first switching means for energizing the operating means of the first relay means to close the switch means thereof when the first switching means is moved to closed circuit position, second switching means having a starting position and an off position and an intermediate position, second relay means including operating means and switch means operated thereby, circuit connections controlled by the second switching means and the switch means of the rst relay means for energizing the operating means of the second relay means to close the switch means thereof when the second switching means is moved to the starting position and the switch means of the first relay means is closed, circuit connections controlled by the second switching means, the switch means of the first relay means and the switch means of the second relay means for maintaining energization of the operating means of the second relay means to maintain the switch means of the second relay means closed while the second switching means moves from its starting position and through its intermediate position whereupon opening of the switch means of the rst relay means or movement of the second switching means to its off position opens the switch means of the second relay means, and a circuit for controlling the electrically operated device by the switch means of the second relay means to operate the electrically operated device only when the switch means of both relay means are closed.

8. In a control system for an electrically operated device, the combination of, first switching means, nrst rel ay means including operating means and switch means operated thereby, circuit connections controlled by thc first switching means for energizing the operating means of the rst relay means to close the switch means thereof when the first switching means is moved to closed circuit position, second switching means having a starting position and an off position and an intermediate position, second relay means including operating means and switch means op- A erated thereby, circuit connections controlled by the second switching means for energizing the operating means of the second relay means to close the switch means thereof when the second switching means is moved to the starting posi-- tion, circuit connections controlled by the switch means of the rst relay means and the switch means of the second relay means for maintainingv energization of the operating means of the second relay means to maintain the switch means of the second relay means closed, whereupon opening of the`switch means of the first relay means opens the switch means of the second relay means, circuit connections controlled by the second switching means in control of the energization of the operating means of the second relay means to open the switch means thereof when the second switching means is moved through its intermediate position to the off position, and a circuit connecting the switch means of both relay means in series with the electrically operated device to operate the device only when the switch means oi both relay means are closed.

9. In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said appayratus of, a rst relay including operating means and switch means operated thereby, a second relay including operating means a'nd switch means operated thereby, rst switching means, circuit connections controlled by the first switching means to energize the operating means of the first relay for closing the switch means thereof, second switching means, circuit connections controlled by the second switching means and the switch means of the rst relay to energize the operating means of the second relay for closing the switch means thereof providing the switch means of the rst relay is closed, whereupon opening of the switch means of the rst relay opens the switch Ali) means of the second relay, means responsive to pressure on the high pressure side of the refrigerating apparatus for operating one of the switching means, means responsive to a condition which is a measure of evaporator temperature for operating the other switching means, and circuit connections controlled by the switch means of the second relay for operating the compressor only when the switch means of both relays are closed.

10. In a refrigeration system including a refrigeratng apparatus having a compressor and evaporator means, the combination with said apparatus'of a first relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, rst switching means| circuit connections controlled by the first switching means to energize the operating means of the first relay for closing the switch means thereof, second switching means, circuit connections controlled by the second switching means and the switch means of the first relay to energize the operating means of the second relay for closing the switch means thereof providing the switch means f the first relay is closed, whereupon opening of the switch means of the iirst relay opens the switch means of the second relay, means responsive to pressure on the high pressure side of the refrigerating apparatus for operating one of the switching means, means responsive to the temperature of the medium being controlled by the evaporator means for operating the other switching means, and circuit connections controlled by the switch means of the second relay for operat ing the compressor only when the switch means of both relays are closed.

11. In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a rst relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, rst switching means, circuit connections controlled by the rst switching means to energize the operating means of the first relay for closing the switch means thereof, second switching means, circuit connections controlled by the second switching means and the switch means of the first relay to energize the operating means of the second relay for closing the switch means thereof providing the switch means of the first relay is closed, whereupon opening of the switch means of the first relay opens the switch means of the second relay, means responsive to a condition which is a measure of evaporator temperature for operating one of the switching means, means responsive to the ternperature of the medium being controlled by the evaporator means for operating the other switching means, and circuit connections controlled by the switch means of the second relay for operating the compressor only when the switch means of both relays are closed.

12. In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a rst relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, first switching means, circuit connections controlled by the first switching means to energize the operating means of the rst relay for closing the switch means thereof, second switching means having a starting, a stopping and an intermediate position, circuit connections controlled by the second switching means when in its starting position and the switch means of the first relay to initially energize the operating means of the second relay for closing the switch means thereof providing the switch means of the iirst relay is closed, whereupon opening of the switch means of the iirst relay opens the switch means of the second relay, additional circuit connections controlled by the switch means of both theV first and second relays and by said second switching means for maintaining energization of the operating means upon movement of said second switching means from its starting to its intermediate position, means responsive to the temperature of the medium being controlled by the evaporator means for controlling one of said switching means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for controlling the other of said switching means, and a circuit controlled by the switch means of the second relay for operating the compressor only when the switch means of both relays are closed.

13.'In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apn paratus of, a first relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, first switching means, circuit connections controlled by the first switching means to energize the operating means of the first relay for closing the switch means thereof, second switching means having a starting, a stopping and an intermediate position, circuit connections controlled by the second switching means when in its starting position and theswitch means of the first relay to initially energize the operating means of the second relay for closing the switch means thereof providing the switch means of the lirst relay is closed, whereupon opening of the switch means of the first relay opens the switch means of the second relay, additional circuit connections controlled by the switch means of both the rst and second relays and by said second switching means for maintaining energization of the operating means upon movement of said second switching means from its starting to its intermediate position, means responsive to the temperature of the medium being controlled by the evaporator means for controlling one of said switching means, means responsive to a condition which is a measure of evaporator temperature for controlling the other of said switching means, and a circuit controlled by the switch means of the second relay for operating the compressor only when the switch means of both relays are closed. 14. In a refrigeration system including a reirigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a first relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, rst switching means, circuit connections controlled by the first switching means to energize the operating means of the nrst relay for closing the switch means thereof, second switching means having a starting, a stopping and an intermediate position, circuit connections controlled by the second switching means when in its starting position andthe switch means of the first relay to initially energize the operating means of the second relay for closing the switch means thereof providing the switch means of the first relay is closed, whereupon opening of the switch means of the rst relay opens theswitch means of the second relay, additional circuit connections controlled by the switch means of both they first and second relays and by said second switching means for maintaining energization of the operating means upon movement of said second switching means from its starting to its intermediate position, means responsive to the pressure on the high pressure side of the refrigerating apparatus for controlling one of said switching means, means responsive to a condition which is a measure of evaporator temperature for controlling the other of said switching means, and a circuit controlled by the switch means of the second relay for operating the compressor only when the switch means of both relays are closed.

15. In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a nrst relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, a third relay including operating means and switch means operated thereby, first switching means, circuit connections controlled by the first switching means to energize the operating means of the rst relay for closing the switch means thereof, second switching means, circuit connections controlled by the second switching means'and the switch means of the first relay to energize the operating means of vthe second relay for closing the switch means thereof providing the switch means of the iirst relay is closed, whereupon opening of the switch means of the rst relay opens the switch means of the second relay, third switching means, circuit connections controlled by the third switching means and the switch means of the first and second relays to energize the operating means of the third relay for closing the switch means thereof providing the switch means of the first and second relays are closed, whereupon opening of the switch means of the first or second relay opens the switch means of the third relay, means responsive to the pressure on the high pressure side of the I'efrigerating apparatus for operating one of the switching means, means responsive to a condition which is a measure of evaporator temperature for operating another of the switching means, means responsive to the temperature of the medium being controlled by the evaporator means for operating the other switching means, and a circuit controlled by the switch means of the third relay for operating the compressor only when the switch means of all of the relays are closed.

16. In la refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a first relay including operating means and switch means operated thereby, a second relay including operating means and switch means operated thereby, a third relay including operating means and switch means operated thereby, first switching means, circuit connections controlled by the first xswitching means to energize the operating means of the iirst relay for closing the switch means thereof, second switching means, circuit connections controlled by the second switching means and the switch means of the rst relay to energize the operating means of the second relay for closing the switch means thereof providing the switch means of the rst relay is closed, whereupon opening of the switch meansroi'v the iirst relay opens the switch means of the second relay, third switching means, circuit connections controlled by the third switching means and the switch means of the rst and second relays` to energize the operating means of-the third relay for closing the switch means thereof providing the switch means oi the `rst and second relays are closed, whereupon opening of the switch'means of the first or second relay opens the switch means of the third relay, means responsive to the temperature of the medium being controlled by the evaporator means for operating the one of said switching means, means responsive to the pressure on the high pressure side of the refrigerating apparatus for operating another of the switching means,

- means responsive to a condition which is a measure of evaporator temperature forv operating the remaining switching means, a circuit controlled by the switch means of the third relay for operating the compressor only when the switch means of all of the relays are closed, one of said switching means having a starting, a stopping and an intermediate position, and circuit connections'controlled by said one or the switching means and the switching means of its relay to maintain energization of the operating means of such relay when the switching means moves from itsA starting to its intermediate position.

17. In a refrigeration system including a reirigerating apparatus having a compressor and evaporator means, the combination with said ap paratus of, a iirst relay having operating means and switch means operated thereby,a second relay having operating means and switch means operated thereby, iirst switching means having a starting position, an intermediate position and an oi! position, second switching means having a starting position, an intermediate position, and an oil position, circuit connections controlled by the first switching means to energize the operating means of the first relay to close the switch means of the first relay when the iirst switching means is moved to the starting position, circuit connections controlled by the switch means of the iirst relay in control of the operating means of the rst relay to maintain the switch means of the iirst relay closed when the rst switching means moves to its intermediate position and until it moves to its ofi position, circuit connections controlled by the second switching means and the switch means of the rst relay to energize the operating means of the second relay to close the switch means of the second relay when the second switching means is moved to the starting position and the switch means of the first relay is closed, circuit connections controlled by the4 switch means of the iirst relay and the switch means of the second relay in control of the operating means of the second relay to maintain the switch means of the second relay closed when the second switching means moves to its intermediate position and until it moves to its ofi psition, a circuit controlled by the switch means of the second relay for operating the compressor when the switch means of both relays are closed, means responsive to the pressure on the high pressure side of the refrigerating apparatus for moving one of the switching means to the starting position upon a decrease in pressure and to its intermediate position and then to the oi position upon an increase in pressure, and means responsive to a condition which is a measure of evaporator temperature to move the other switching means to the starting position upon an increase in evaporator temperature and to its intermediate position and then to the of! position upon a decrease in evaporator temperature.

18. Ina refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a rst relay having operating means and switch means operated thereby, a second relay having operating means and switch means operated thereby, iirst switching means having a starting position, an intermediate position and anoiI position, second switching means having a starting position, an intermediate position and an oif position, circuit connections'controlled by the first switching means to energize the operating means of the ilrst relay to close the switch means of the rst relay when the first switching means is moved to the starting position, circuit connections controlled by the switch means of the first relay in control of the operating means of the first relay to maintain the switch means of the first relay closed when the first switching means moves to its intermediate position and until it moves to its of! position,

"circuit connections controlled by the second switching means and the switch means of the ffirst relay to energize the operating means of the second relay to close the switch means of the second relay when the second switching means is moved to the starting position and the switch means of the iirst relay is closed, cirswitching means moves to its intermediate position and until it moves to its oii position, 'a circuit controlled by the switch means of the second relay for operating the compressor when the switch means of both relays are closed, means responsive to the pressure on the high pressure side ofthe refrigerating apparatus for moving one of the switching means to the starting position upon a decrease in pressure and to its intermediate and then to the oiI position upon an increase in pressure, and means responsive to the temperature of the medium being controlled-by the evaporator means to move the other switching means to the starting position upon an increase in temperature and to its intermediate and then to the off positionupon a decrease in temperature.

19. In a refrigeration system including a refrigerating apparatus having a compressor and evaporator means, the combination with said apparatus of, a iirst relay having operating means and switch means operated thereby, a second relay having operating means and switch means operated thereby, rst switching means havingmoves to its intermediate position and until it moves to its off position, circuit connections controlled by the second switching means and the switch means of the first relay to energize the operating means of the second relay to close the switch means of the second relay when the second switching means is moved to the starting position and the switch means of the first relay is closed, circuit connections controlled by the switch means of the first relay and the switch means of the second relay in control of the operating means of the second relay to maintain the 'switch means of the second relay closed when the second switching means moves to its intermediate position and until it moves to its off position, a circuit controlled by the switch means of the second relay for operating the compressor when the switch means of both relays are closed, means responsive to the temperature of the medium being controlled by the evaporator means to move one of the switching means to the starting position upon an increase in temperature and to its intermediate and then to the off position upon a decrease in temperature, and means responsive to a condition which is a measure of evaporator temperature to move the other switching means to the starting position upon an increase in evaporator temperature and to its intermediate and then to the oi position upon a decrease in evaporator temperature.

ALWIN B. NEWTON.