US2234250A

US2234250A - Refrigeration control system

Info

Publication number: US2234250A
Application number: US243801A
Authority: US
Inventors: John L Harris
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1938-12-03
Filing date: 1938-12-03
Publication date: 1941-03-11
Anticipated expiration: 1958-03-11

Description

March 11, 19, 41. J. L. HARRIS REFRIGERATION CONTROL SYSTEM Filed Dec. 3, 1938 2 Sheets-Sheet 1 x x (I 8 j may m fiwall v "Fig.

March 11, 1941. J. L. HARRIS 2,234,250

REFRIGERATION CONTROL SYSTEM 7 Filed Dec. 3,, 1938 Z-Sheets-Sheet 2 7 Fig.3

Patented Mar. 11, 1941 UNITED STATES PATENT OFFICE REFRIGERATION CONTROL SYSTEM John L. Harris, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn a corporation of Delaware Application December 3, 1938, Serial No. 243,801

20 Claims.

This invention relates to control systems for a refrigerating apparatus and particularly to control systems for a refrigerating apparatus having a plurality of evaporators.

The prime object of this invention is to provide a control system for a refrigerating apparatus having a plurality of evaporators wherein refrigerant is normally supplied to one of the evaporators at all times regardless of the frost condition of the evaporator and wherein refrigerant is supplied to the other evaporator upon a demand for cooling provided the other evaporator is defrosted. In other words, this invention contemplates the control of a plurality of evaporators to give desired temperature control and to defrost those evaporators which it is desirable to defrost and not defrost the other evaporators. The evaporators which are defrosted may be utilized for cooling storage compartments walkin boxes or the like, while the evaporators which do not require defrosting may be utilized for cooling, freezing or hardening devices, soda fountains, water coolers, and the like.

The manners in which this sequence of operation is accomplished also form objects of this invention.

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

drawings in which Figure 1 is a diagrammatic illustration of one form of this invention,

Figure 2 is a diagrammatic illustration of another form of the invention, and

Figure 3 is a diagrammatic illustration of still another form of the invention.

Referring now to Figure 1 a pair of fixtures to I be cooled are designated at It and l I. The fixture l0 may be a storage compartment, walk-in box,

=10 or the like which is cooled by an evaporator l2 and fixture H may be a freezing or hardening chamber, a soda fountain, or the like cooled by an evaporator I3. Due to the evaporator l2 being located in an air space for cooling the same,

43 moisture will collect and freeze upon this evaporator thereby making defrosting of thisevaporator necessary. The evaporator l3 ;which is provided for chilling a substance which does not freeze on the coil is not subject to frosting and consequently it is unnecessary to defrost this evaporator.

Refrigerant is supplied to the evaporators l2 and I3 by a refrigerating apparatus generally designated at l4 which may comprise a compressor l5 operated by'an electric motor Ii. Compressed refrigerant is delivered from the compressor l5 through ahigh pressure line H to a condenser l8 and condensed refrigerant is collected in a receiver l9. Liquid refrigerant flows from the receiver I!) through a liquid line l to ,the evaporators l2 and I3 which are arranged iii parallel in this embodiment of the invention. Evaporated refrigerant is withdrawn from the evaporators l2 and I3 through a suction line 2| by the compressor IS. The supply of refrigerant to the' evaporator I2 is regulated by the usual thermostatic expansion valve 23 and is turned on and off by a solenoid valve 24. The supply of refrigerant to the evaporator I3 is controlled by the usual thermostatic expansion valve 25. A 15 check valve 26 located on the discharge side of the evaporator I3 is utilized to prevent the back flow of refrigerant into the evaporator l3 during the defrosting cycle of evaporator l2.

The compressor motor I6 is controlled by a 39 relay or starter generally designated at 28 and the relay or starter is in turn controlled by a suction pressure controller generally designated at 29 and a temperature responsive controller generally designated at 3|! responsive to the tempera- 35 ture within the fixture III. The temperature responsive controller 30 additionally controls the solenoid valve 24 to turn on and oil. the supply of refrigerant to the evaporator I2.

The relay or starter 28 may comprise an operating coil 32 for

operating switch arms

33 and 34 with respect tocontacts 35 and 36. When the operating coil 32 is energized the

switch arms

33 and 34 are moved into, engagement with the contacts 35 and 36, respectively, and when the oper- 35 ating coil 32 is deenergized the switch arms are moved out of engagement with their respective contacts by means of springs, gravity, or other means (not shown).

The suction pressure responsive controller 23 4 may comprise a bellows 33 connected by a pipe '39 1 to the suction pressure line 2|. The bellows 33 operates a lever 40, preferably made of insulating material, against the action of an adjustable tension spring 4|. Thelever 43 carries

contacts

42, 43, and 44, the contacts 43 and 44 being electrically connected while the contact 42 is electrically insulated from the contacts 43 and 44. The

contacts

42, 43, and 44 are adapted upon a rise in suction pressure to sequentially engage

stationary contacts

45, 46, and 41, respectively. Upon a decrease in suction pressure the movable contacts sequentially disengage their respective stationary contacts in a reverse order. For purposes in suction pressure contact 42 engages contact 45 at 15 lbs., contact 43 engages contact 46 at 25 lbs, and contact 44 engages contact 41 at 35 lbs. Upon a decrease in pressure contacts 44 and 41 separate at 35 lbs., contacts43 and 46 separate at 25 lbs., and

contacts

42 and 45 separate at 15 lbs. For purposes of illustration it is also assumed that the defrosting value of the suction pressure is between 25 lbs. and 35 lbs. so that it is impossible to engage the contacts 44 and 41 until the evaporator I2 has defrosted while contacts 43 and 46 may engage even though the evaporator I2 has not defrosted. Accordingly, the suction pressure responsive controller 29 may be considered a defrosted condition" responsive controller.

The temperature responsive controller 30 responsive to the temperature within the fixture I0 may comprise a bellows 49 charged with a volatile fluid for operating a lever 50 against the action of an adjustable tension spring I. The lever 50 operates a mercury switch 52 which may be of the general form shown and described in application Serial No. 167,755 filed by Harold T. Olson on October '7, 1937. The mercury switch 52 is provided with

left electrodes

53, 54, and 55 and

right electrodes

56, 51 and 59, the electrodes 55 and 56 being electrically connected together. The mercury switch 52 is provided witla ridge or detent 58 in the lower wall thereoi to cause the mercury in the mercury switch to separate from the

contacts

53, 54, and 55 before it engages the

contacts

56, 51 and 59 upon an increase in temperature. Upon a decrease in temperature the ridge or detent 58 holds some of the mercury in engagement with

contacts

56, 51 and 59 while the rest of the mercury engages the

contacts

53, 54, and 55 until the switch 52 is tilted sufiiciently far to cause the mercury to I disengage. the electrodes 56, 51 and- 59. In this manner upon an increase in temperature the switching actions performed by the switch 52 are non-overlapping, but are overlapping upon a decrease in temperature. For a more thorough description of the sequence of operation of the u y switch 52 reference is made to the above referred to Harold, T. Olson application. For

purposes of illustration it is assumed that the switch 52 is tilted to the position wherein the

electrodes

56, 51 and 59 are bridged at 42 and that theswitch 52 is tilted to the position where-- in the

electrodes

53, 54, and 55 are bridged when the temperature within the fixture I6 decreases to 40.

Power is supplied to the compressor motor I6.

the solenoid valve 24, and the control system.

by means of line wires 60 and 6| leading from some source of power (not shown).-

Assuming now that the temperature within the fixture I0 is below 40 so that no cooling is required in the fixture I 6' the switch 52 of the temperature responsive controller '30 will be in the position shown in Figure 1. When the suction pressure rises to 25 lbs. to cause the contacts 92 and 43 to engage contacts 45 and 46 a circuit is completed from the line wire 69 through wire 62,

electrodes

55 and 53, wire 63, contacts 46 and 43, wires 64 and 65, operating coil 32 and wire 66 back to the other line wire 6| Completion of this circuit energizes the operating coil 32 to move the

switch arms

33 and 34 into engagement with the contacts 35 and 36. Move- 1 ment of the switch arm 94 into engagement with the contact 36 completes a load circuit for the I compressor motor I9 which may be traced from the line wire 60 through wire 61, switch arm 34,

sure decreases to 15 lbs.

contact 36,- wire 68, compressor motor I6, and wires 69 and ,back to the other line wire 6|. Hence, whenever the relay or starter 28 is pulled in the compressor motor I6 and hence the compressor I5 is placed in operation.

Movement of the switch arm 33 into engagement with the contact 35 completes a maintaining circuit for the operating coil 32 which may be traced from the line wire 69 through wire 62,

electrodes

55 and 54, wires H and 12,

contacts

45 and 42, wire 13, contact 35, switch arm 33, wires 14 and 65, operating coil 32, and wire 66 back to the other line wire 6I. Completion of this circuit maintains the operating coil 32 energized and hence the compressor I5 inoperation until the suction pressure decreases to lbs. to separate the

contacts

42 and 45. Accordingly when the temperature responsive controller 30 within the fixture I0 is satisfied the relay or starter 28 and hence the compressor I5 are controlled by the suction pressure controller 29 to maintain the suction pressure between 15 lbs, and lbs. This operation of the compressor I5 therefore supplies refrigerant to the evaporator I3 for cooling the fixture I I but since the solenoid valve 24 associated with the evaporator I 2 is closed the evaporator I2 is starved of refrigerant and therefore performs no cooling action.

Assume now that the temperature Within the fixture Ill rises to 42 to tilt the switch 52 to a position to bridge the

electrodes

56, 51 and 59. As pointed out above the

electrodes

53, 54, and 55 are unbridged before the

electrodes

56, 51 and 59 are bridged and therefore if the compressor I5 is operating at this time the unbrid'ging of the

electrodes

53, 54, and 55 stops the compressor. Bridging of the

electrodes

56, 51 and 59 completes a circuit from the line wire 60 through wire 62, electrodes 56 and 59, wire 16, solenoid valve 24, and

wires

18 and 18 back to the other line wire 6| Accordingly when the temperature within the'fixture It increases to 42 the solenoid valve 24 is opened to supply refrigerant to the evaporator I2.

However, the compressor I5 cannot start. until such time as the suction pressure increases to a defrosting value of 35 lbs. to close the contacts 54 and 41. When this occurs a circuit is completed from the line Wire 60 through wire 62, electrodes 56 and 51, wires 19, and 86, contacts 41 and 44, wires 64 and 65, operating coil 32, and wire 66 back to the other line wire 6| Completion of this circuit pulls in-the relay or starter 28 to start the compressor 55. Pulling in of the relay or starter 28' completes a maintaining circuit which may be traced from the line wire 60 through wire 62,

electrodes

55 and 51, wires 19, BI, and 12,

contacts

45 and 42, wire 53, contact 35, switch arm 33, -wires 14 and 65, operating coil 32, and wire 66 back to the other line wire 6I. Completion of this circuit maintains the relay or starter 28 pulled in until the suction pres- Accordingly, when the temperature responsive controller calls for cooling, the compressor I5 is stopped if it is running and if the suction pressure is below lbs, the solenoid valve 24 is opened, and when the evaporator i2 has defrosted to cause the suction pressure to rise to 35 lbs, the compressor i5 is placed in operation to supply refrigerant to the evaporator I2. The check valve 26 connected on the discharge side of the evaporator I3 prevents the back flow of refrigerant into the evaporator It so that the evaporator I3 will not defrost while the evap rator I2 is defrosting.

If when the temperature responsive controller 38 is calling for cooling and the' suction pressure decreases to 15 lbs. to stop the compressor I5, the compressor cannot again start until the suction pressure increases to the defrosting value of lbs. whereby defrosting of the evaporator I2 is always assured.

When the temperature within the fixture I8 decreases to 40 the mercury switch tilts from the on position to the position shown in Figure 1 and as pointed out above the mercury in the mercury switch 52 engages the

contacts

53, 54, and 55 before it disengages the

contacts

58, 51 and 59 so that if the compressor is in operation it will be maintained in operation by the overlapping action of the mercury switch 52. When the switch 52 is tilted sumciently far to cause the mercury to disengage the

electrodes

56, 51 and 59 the solenoid valve 24 is closed to starve the evaporator I2 and hence interrupt the cooling action performed thereby. From the above it is seen that the control system of Figure 1 provides cooling at all times in the fixture II and also provides temperature and defrosting control for the fixture I8. In other words, the refrigerating system of Figure 1 provides a freezing or hardening action within the fixture I I at all times and provides accurate temperature control accompanied with a defrosting action within fixture I8.

, Referring now to Figure 2 a fixture to be cooled is designated at 85, this fixture being provided with a freezing chamber 88 and a storage compartment 81. An evaporator 88 located within the freezing chamber 86 cools, hardens or freezes a suitable substance located in a container 84 and an evaporator 89 located within the storage compartment 81 maintains desired temperatures within the storage compartment 81. As shown the

evaporators

88 and 89 are connected in series with respect to each other, a check valve 98 being located between the evaporators to prevent the back flow of refrigerant from the evaporator 89 into the evaporator 88 during the defrosting periods.

Refrigerant is supplied to the

evaporators

88 and 89 by means of a refrigerating apparatus generally designated at 92 and comprising a compressor 93 driven by an electric motor 94. Compressed refrigerant flows from the compressor 93 through a high pressure line 95 into a condenser 98 and condensed refrigerant is collected

orators

88 and 89 through a suction line 99 by I the compressor 93.

An expansion valve I 88 regulates the supply of refrigerant to the

evaporators

88 and 89, the expansion valve I08 being of the thermostatic type having a capillary tube I88 connected through a three-way valve I82 to bulbs I83 and I84. The bulb I83 is located at the discharge end of the evaporator 88 and the bulb I84 is located at the discharge end of the evaporator 89. The bulbs I83 and I84 are charged with a volatile fluid so as to operate the thermostatic expansion valve I88 in accordance with the temperature of the refrigerant leaving the evaporators. The three-Way valve I82 operated by a solenoid I85 selects which bulb I83 or I84 shall control the thermostatic expansion valve I88. When the solenoid I 85 is energized the thermostatic expansion valve I88 is connected to the bulb I84 to be cury switch I81. When the solenoid I85 is energized the switch I81 is tilted to bridge electrodes I98 and I9I and when it is deenerglzed, electrodes I92 and I93 are bridged. To insure that no cold gaseous refrigerant will enter the evaporator 89 when the solenoid I85 is deenergized an electric heating coil I89 located in the connection between the

evaporators

88 and 89 may be utilized to heat the gaseous refrigerant flowing thereby. When the solenoid I85 is deenergized to prevent the supply of liquid refrigerant to the evaporator 89, the refrigerant therein will be superheated by this heating coil and hence the evaporator 89 will defrost.

The compressor motor 94 and hence the compressor 93 is controlled by a relay or starter generally designated at I I I. The relay or starter I II is, in turn controlled by a suction pressure responsive controller H2 and a temperature responsive controller I I3 responsive to the temperature within the storage compartment 81. A temperature responsive controller II4 responsive to the temperature and hence the defrosted condition of the evaporator 89 acts in conjunction with the temperature responsive controller II3 to control the heating element I89 and the solenoid "I85.

The relay or starter III may comprise an operating coil II-8 for moving switch arms H1 and H8 into engagement with contacts H9 and I28 when energized. When the operating coil II8,is deenergized the switch arms are moved out of engagement with their respective contacts by means of springs, gravity, or other means (not shown).

The suction pressure responsive controller II2 may comprise a bellows I22 connected by a pipe I23 to the suction line 99 for operating a lever I24, preferably made of insulating material, against the action of an adjustable tension spring- I25. The lever I24 sequentially operates contacts I26, I21, and I 28 with respect to stationary contacts I29, I38, and I3I, the contacts I21 and I28 being electrically connected together and the contact I28 being electrically insulated from the contacts I21 and I28. For purposes of. illustration it is assumed that the parts are so arranged that the contacts I28 and I21 engage and disengage at erates a lever I86 which in turn operates a mer- 15 lbs., the contacts I21 and I38 engage and 81 decreases to' 40 electrodes I39, I40, and I are bridged and when the temperature increases to 42 the electrodes E42, I43, and I44 are bridged. The parts are so arranged that upon an increase in temperature the electrodes I42, I43 and I44 are bridged before the electrodes I39, I40, and MI are unbridged and conversely upon a decrease in temperature the electrodes I39, I 40, and MI are bridged before the electrodes I42, I43, and I44 are unbridged. In other words, the switching action performed by switch I38 overlaps in both directions.

The frost condition responsive controller H4 responding to the temperature of the evaporator 89 may comprise a bellows I45 connected by a capillary tube to a bulb I 46 mounted on the evaporator 89. The bulb I46 is charged with a volatile fluid so that the bellows I45 is operated in accordance with changes in temperature of the evaporator 89. The bellows I45 operates a lever I48 against the action of an adjustable tension spring I41, the lever I48 in turn operating a double ended mercury switch I49 provided with right electrodes I50 and I 5I and left electrodes I52 and I 53. For purposes of illustration it is assumed that the parts are so arranged that when the temperature of the evaporator 89 decreases to 30 the electrodes I5I and I50 are bridged and when the temperature increases to 34 the electrodes I52 and I53 are bridged. The parts are so arranged that the switching action performed by the switch I49 is not overlapping, that is, the electrodes I52 and I53 are unbridged before the electrodes I50 and I5I are bridged and vice versa the electrodes I50 and I5I are unbridged before the electrodes I52 and I53 are bridged.

Power is supplied to'the compressor motor 94, the solenoid I 05,- the heating element I09, and

. the control system by means of line wires I55 and I56 leading from some source of power (not shown).

Assume now that the temperature within the storage compartment 81 is 40 whereupon the temperature responsive controller II3 assumes the position shown in Figure 2. The solenoid I05 is deenergized and the bulb I03 is in control of the thermostatic expansion valve I whereupon liquid refrigerant is supplied to the evaporator 88 but the refrigerant in the evaporator 89 is superheated so that the evaporator 89 does not perform a cooling function. When the suction pressure increases to 25 lbs. to close the contacts I26 and I 29 and the contacts I21 and I30 9. circuit is completed from the line wire I55 through wires I58 and I59, electrodes HI and I39, wire I60, contacts I30 and I21, wire I6I,' operating coil II 6, and wire I62 back to the other-line wire I56. Completion of this circuit energizes the operating coil II6 to move the switch arms H1 and I I8 into engagement with the' contacts H9 and I20, respectively. Movement of the switch arm II8 into engagement with the contact I20 completes a circuit from the line wire I 55 through wire I63, switch'arm II8, contact I20, wire I64, electric motor 94, and wire I65 back to the other line wire I56. Completion of this circuit operates the compressor motor 94 and hence the compressor 93 to supply refrigerant to the evaporator 88.

Movement of the switch arm II1 into engagement with the contact II9 completes a maintaining circuit for the operating coil II 6 which may be traced from the line wire I55 through Wires. I58 and I59, electrodes HI and I40, wires I61,

I68, and I69, contacts I29 and I26, wire I10, contact II9, switch arm II1, wire "I, operating coil I I6 and wire I62 back to the other line wire I56. Completion of this circuit maintains the relay or starter III pulled in and the compressor 93 in operation until the suction pressure decreases to 15 lbs. By reason of the above arrangement when the temperature responsive controller II3 is satisfied the compressor 93 is operated to maintain the suction pressure between 15 lbs. and 25 lbs. to supply refrigerant to the evaporator 88. Under these conditions the expansion valve I00 is undenthe control of the bulb I03 so that no liquid refrigerant is supplied to the evaporator 89 and hence the evaporator 89 is not performing a cooling function.

As long as the evaporator 89 is frosted the temperature responsive controller II4 will bridge the electrodes I50 and II to complete a circuit from the line wire I55 through wires I58 and I13, electrodes I5I and I50, wire I14, electrodes I92 and I 93 of the mercury switch I01, wire I15, heater eiement I09, and wires I16 and I 11 back to the other line wire I56. Completion of this circuit energizes the heater element I09 to heat the refrigerant flowing to the evaporator 89 so that the refrigerant in the evaporator 89 will be superheated and hence cause defrosting of the evaporator 89. When this evaporatof'becgmes defrosted, electrodes I50 and I5I will become unbridged for deenergizing the heating element I09.

When the temperature within the storage compartment 81 increases to 42 the electrodes I42, I43, and I44 are bridged and when the suction pressure increases to 35 lbs. a circuit is completed from the line wire I55 through wires I58 and 859, electrodes I42 and I43, wires I19, I68, and I80, contacts I3I and I28, wire IGI, operating coil I I6 and wire I62 back to the other line wire I56. Completion of this circuit pulls in the relay or starter I II to operate the compressor 92. Pulling in of the relay or starter III completes a maintaining circuit which may be traced from the line wire I55 through wires I58 and I59, electrodes I42 and I43, wires I19, I68, and .I 69,. contacts I 29 and I26, wire I10, contact II9, switch arm II1, wire I1I, operating coil H6, and wire I62 back to the other line wire I56. Accordingly when the temperature responsive controller II3 is calling for cooling the compressor 92 is controlled by the suction pressure controller I I2 to maintain the suction pressure between 15'lbs. and 35 lbs. and if the compressor stops during the time that the temperature responsive controller II3 is calling for c oling, the compressor cannot be restarted until uch time as the suction pressure rises to a defrosting value whereby defrosting of the evaporator 89 is assured. The check valve 90 preventsthe back flow of refrigerant into the evaporator 88 during this defrosting cycle. If however the compressor 93 is in operation when the temperature responsive controller I I3 is operated to call for cooling, the compressor will remain in operation by reason of the overlapping action of the mercury switch I38.

When the evaporator 89 is defrosted the temperature responsive controller II4 operates the switch I49 to bridge the electrodes I52 and I53 and a circuit is thereupon completed from the line wire I through wires I58 and I59, electrodes I42 and I44, wires I82 and l83, electrodes I53 and I52, wires I84 and I85; solenoid I05 and wires I86 and I11 back to the other line wire I56. Completion of this circuit energizes the solenoid I05 to shift the control of the thermostatic expansion valve I00 from the bulb I03 to the bulb I04 so that liquid refrigerant will be supplied to the evaporator 89 to cause the evaporator 89 to perform a cooling function. As pointed out above energization of the solenoid I05 bridges the electrodes I90 and I9I of the mercury switch I01 and this completes a maintaining circuit for the solenoid I05 which is independent of the electrodes I52 and I53 of the temperature responsive controller II4. This maintaining circuit may be traced .from the line wire I55 through wires I58 and I59, electrodes I42 and I44, wires I82 and I88, electrodes I90 and I9I of the mercury switch I01, wires I89 and I85, solenoid I05, and wires I86 and I11 back to the other line wire I56. Completion of this circuit maintains the solenoid I05 energized as long as the temperature responsive controller H3 is calling for cooling. Energization of the solenoid I05 also unbridges the electrodes I92 and I93 to prevent energization of'the heater I09 when liquid refrigerant is being supplied to the evaporator 89.

When the temperature within the storage compartment 81 decreases to 40 the mercury switch I I3 is tilted to the position shown in Figure 2 and the solenoid I05 is deenergized to place the expansion valve I00 under the control of the bulb I03 to interrupt the supply of liquid refrigerant to the evaporator 89 and the compressor 93 is placed under the control of the suction pressure controller II2 to maintain the suction pressure between 15 lbs. and 25 lbs. If the temperature of the evaporator 89 is below freezing indicating that frost is present on the evaporator .89 the heating element I09 is energized to hasten the defrosting of the evaporator 89.

By reason of the control arrangement'pf Figure 2, when the temperature responsive controller H3 is satisfied the compressor is operated to maintain a suction pressure between 15 lbs. and 25 lbs. and the expansion valve I00 is adjusted to supply liquid refrigerant to the evaporator 88 but not to the evaporator 89 whereupon only the evaporator 88 performs a cooling function. When the temperature responsive controller II3 calls for cooling the expansion valve I00 is adjusted to supply refrigerant to the evaporator 89 provided the evaporator 89 has defrosted so that both

evaporators

88 and 89 will perform a cooling function. If the compressor should cut out from a low suction pressure when refrigerant is being supplied to the evaporator 89 it cannot be restarted until the evaporator 89 has defrosted. Accordingly the arrangement of Figure 2 provides for substantially continuous cooling by the evaporator 88 and provides automatic temperature control of the evaporator 89 to maintain desi ed temperatures within the storage compartment 81 and to cause intermittent defrosting of the evaporator 89.

Referring now to Figure 3, three fixtures are designated at 200, 20I, and 202. The fixtures 200 and 20I are cooled by evaporators 203 and 204, it being desirable to intermittently defrost the evaporators 203 and 204. The fixture 202 is cooled by an evaporator 205 and in this instance it is not desirable to intermittently-defrost the evaporator 205. The fixtures 200 and 20I may be storage compartments, walk-in boxes, and the like while the fixture 202 may be a freezing or hardening compartment or the like wherein it is desirable to maintain low temperatures. Refrigerant is supplied to the

evaporators

203, 204, and 205 by mea 's of a refrigerating apparatus generally design ted at 206 and which may comprise a compressor 201 operated by an electric motor 208. Compressed refrigerant fiows from the compressor 206 through a high pressure line 209 into a condenser 2| 0 and condensed refrigerant is collected in a receiver 2I I. Liquid refrigerant fiows from the receiver 2 through a liquid line 2I2 to the

evaporators

203, 204, and 205 arranged in parallel. Evaporated refrigerant is withdrawn from the

parallelarranged evaporators

203, 204, and 205 through a suction line 2I3 by the compressor 201. Evaporators 203, 204 and 205-are provided with the conventional thermostatic expansion valves 2I4, H5, and 2I6, respectively, to regulate the flow of refrigerant into these evaporators. The

evaporators

203, 204, and 205 are also provided with solenoid valves 2", 2I8, and

"troller 224 responsive to the temperature .ofthe evaporator 203. In a like manner the solenoid valve 2I8 of the fixture I is controlled by a relay 225 which in turn is controlled by a temperature responsive controller 226 responsive to the temperature within the fixture 20I and a frost condition responsive controller 221 responsive to the temperature of the evaporator 204. The solenoid valve 2I9 for controlling the supply of refrigerant to the evaporator 245 iscontrolled by a temperature responsive controller 228 re- .sponsive to the temperature within the fixture The suction pressure responsive controller 22I maycomprise a bellows 230 connected by a pipe 23I to the suction line 2I3 for operating a lever 232 against the action of an adjustable tension spring 233. The lever 232 operates a mercury switch 234 and for purposes of illustration it is assumed that the mercury switch 234 is closed when the suction pressure increases to 25 lbs. and is opened when the suction pressure decreases to 15 lbs.

The relay 222 which controls the solenoid.

valve 2| 1 may comprise an operating coil 236 for operating

switch arms

231, 238, and 239 with respect to

contacts

240, 24I, and 242, respectively. When the operating coil 236 is energized the switch arms 231 and 239 are moved into engagement with

contacts

240 and 242, respectively, and the switch arm 238 is moved out of engagementwith the contact 2. When the relay coil 238 is deenerglred the switch arms 231 and 239 are moved out of engagement ,with their respective.

contacts

240 and 242 and the switch arm .238 is moved into engagement with the contact 2 by means of springs, gravity, or other means (notshown) The relay 225 is exactly the same as the relay 222 and therefore like reference characters for like parts have been utilized.

The temperature responsive controller223 responsive to the temperature within the fixture 200 may comprise a bellows 244 charged with a volatile fluid for operating a lever 245 against the action of an adjustable tension spring 246. The lever 245 operates a mercury switch 241 and for purposes of illustration it is assumed that the mercury switch is tilted to a closed position when the temperature the fixture 200 rises to 42 and is tilted to the open position as shown in Figure 3 when the temperature decreases to 40. .A heater 248 may be provided for artificially heating the thermostatic bellows 244 when the mercury switch 241 is open to provide a cold anticipating function. The construction of the temperature

responsive controllers

226 and 228 is exactly the same as that of the temperature responsive controller 233 and therefore like reference characters have been utilized for like parts. As is evident, the various temperature responsive controllers may be set to maintain different temperature conditions within the various fixtures.

The defrosted condition responsive controller 224 responsive to the temperature of the event)- rator 203 may comprise a bellows 250 connected by a capillary tube 25! to a bulb 252 carried'by the evaporator 203. The bulb 252 is charged with a volatile fluid so that the bellows 250 is operated in accordance with the temperature of the evaporator 203; The bellows 250 operates a lever 253 against the action of an adjustable tension spring 25%. The lever 253 operates a mercury switch 255 and for purposes of illustration it is assumed that the mercury switch 255 is moved to a closed position when the tem-- perature of the evaporator increases to 34 and is moved to an open position when the temperature of the evaporator decreases to 30. Hence the mercury switch 255 is closed. when the evaporator 203 is defrosted. The construction of the frost condition responsive controller 221 associated with the fixture 20l is exactly the same as that of the frost condition responsive controller 224 and therefore like reference characters for like parts have been utilized. It is here noted that the fixture 202 is not provided with a frost condition responsive controller.

Power is supplied to the compressor motor 208, the solenoid valves 2H, H8, and 2H! and to the control system by means of line wires 251 and '258 leading from some source of power (not shown).

When the suction pressure increases to 25 'lbs. the switch 234 of the suction pressure responsive controller MI is closed to complete a circuit from the line wire 251 through wire 25?, mercury switch 234, wire 260, compressor motor 208, and wire 26l back to the other line wire 258 Completion of this circuit operates the compressor motor 208 and hence the compressor 201 until such time as the suction pressure decreases to 15 lbs. Accordingly the compressor 221 is operated to maintain the suction pressure between 15 lbs. and 25 lbs.

When the temperature responsive controllerand wire 265 back to the other line wire solenoid valve 2M is closed to starve the evaporator 205 whereupon the cooling action thereof is interrupted. In this manner desired tempera 200 decreases to 40. temperature responsive controller 223 of the fixture conditions are maintained within the fixture 202.

Referring now to the control apparatus for the fixture 200 of Figure 3 it is seen that when the temperature responsive controller 223 is satis- 5 fled causing relay 222 to assume the position shown, a circuit is completed from the line wire 251 through wire 261, contact 2, switch arm 238, wire 268, auxiliary heater 248, and Wire 269 back to the other line wire 258. This heater supplies auxiliary heat to the temperature responsive controller 223 to cause the temperature responsive controller 223 to assume the cut in value of 42 before the temperature of the fixture has actually risen to 42. When the temperature of the temperature responsive controller 223 rises to 42 and when the evaporator 203 has defrosted to close the switch 255 of the frost condition responsive controller 224, a circuit is completed from the line wire 251 through wire 2H, mercury switch 241, wire 212, mercury switch 255, wire 213, operating coil 236, and wire 214 back to the other line wire 258. Completion of thiscircuit energizes the operating coil 236 to move the switch arm 238 out of engagement with the con- 2 tact 2 thereby interrupting the circuit through the auxiliary heater 248 and to move the switch arms 231 and 239 into engagement with

con tacts

240 and 242.

Movement of the switch arm 239 into engage- 3 ment with the contact 242 completes a circuit from the line wire 251 througl. wire 261, contact 242, switch arm 239, wire 216, solenoid valve 2", and wire 211 back to the other line wire 250. Completion of this circuit opens the solenoid 3 valve 2I1 to supply liquid refrigerant to the evaporator 203.

Movement of the switch arm 231 into engagement with the contact 240 completes a maintaining circuit for the operating coil 236 which is independent of the switch 255 of the frost condition responsive controller 224. This may be traced from the line wire 251 through wire 21l, switch 241, wires 212 and 219, contact 240, switch arm 231, operating coil 236, and wire 214 back 4 to the other line wire 258. This maintaining circuit maintains the solenoid valve 2l1 open until such time as the temperature within the fixture Accordingly, when the ture 2130 calls for cooling the solenoid valve 2" is opened to supply liquid refrigerant to the evaporator 203 providing the evaporator 203. has clefrosted. The solenoid valve 2l1 is maintained opened until such time as the temperature responsive controller 223 becomes satisfied. In this manner desired temperature conditions are maintained within the fixture 200 and the evaporator 203 is defrosted every time that the sole- 6 hold valve 2 l 1 is closed.

The manner in which the relay 225 associated with the fixture 20! controls the solenoid valve 2li3 and the manner in which the relay 225 is controlled by the temperature responsive con- 6 trailer 226 and the frost condition responsive controller 221 is exactly the same as that outlined above in connection with fixture 200 and therefore like reference characters for like wiring have been utilized. 7

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

I claim as my invention:

1. In a control system for a refrigerating apparatus having a compressor, first and second evaporator means, a high pressure line connecting the compressorand condenser, a liquid line connecting the condenser and the evaporator means and a suction line connecting the evaporator means and the compressor, it being desirable to defrost the second evaporator means and not the first, the combination of, valve means iii the liquid line for turning on and ofi the supply of liquid refrigerant to'the second evaporator means, thermostatic means responsive to a temperature condition produced by the second evaporator means, thermostatic means responsive to the defrosted condition of the second inlet side of the evaporator means for turning on and off the supply of refrigerant to the evaporator means, thermostatic means responsive to a temperature condition produced by the evaporator means, thermostatic means responsive to the defrosted condition of the evaporator means, and means controlled by both thermostatic means to operate the valve means upon a call for cooling to supply refrigerant to the evaporator means only after the evaporator means has defrosted.

3. In a control system for a refrigerating apparatus having a plurality of evaporators for cooling a plurality of fixtures and a common compressor for supplying refrigerant to and withdrawing refrigerant from all of the evaporators, the combination of, valve means on the inlet side of each evaporator for controlling the supply of refrigerant to its associated evaporator, means associated with each fixture and including means responsive to the temperature of" the fixture and means responsive to the temperature of the evaporator of the fixture for opening the valve means of that fixture upon a call for cooling providing the evaporator of that fixture has defrosted whereby individual temperature and defrosting control of each fix'ture is obtained.

4. In a control system for a refrigerating apparatus having first and second evaporators connected in series and a compressor wherein defrosting of the second evaporator is desired but not of the first, the combination of, an expansion valve for controlling the supply of refrigerant to the evaporators, control means for the expansion valve operable to maintain liquid refrigerant in the first and second evaporators or liquid refrigerant in the first evaporator and superheated refrigerant in the second evaporator, thermostatic means responsive to a temperin the liquid line for normally allowing liquid refrigerant to be supplied to the first evaporator means but for turning on and off the supply of liquid refrigerant to the second evaporator means, control means responsive to a temperature condition produced by the secondevaporator means for operating the valve means to supply liquid refrigerant to the second evaporator means upon a call for cooling, and means responsive to suction pressure, operative when the valve means is operated to supply liquid refrigerant to the second evaporator means, for starting the compressor only when the suction pressure has increased to a defrosting value and for starting the compressor at a suction pressure below the defrosting value when thevalve means is operated to prevent the supply of liquid refrigerant to the second evaporator means.

6. In a control system-for a refrigerating apparatus having a compressor, first and second evaporator means, a high pressure line connecting the compressor and condenser, a liquid line connecting the condenser and the evaporator means and a suction line connecting the evaporator means and the compressor, it being desirable to defrost the second evaporator means and not the first, the combination of, valve means in the liquid line for normally allowing liquid refrigerant to be supplied to the first evaporator means but for turning on and off the supply of liquid refrigerant to the second evaporator means, control means responsive to a temperature condition produced by the second evaporator'means for operating the valve means to supply liquid refrigerant to the second evaporator means upon a call for cooling, means responsive to suction pressure, operative when the valve means is operated'to supply liquid refrigerant to the second evaporator means, for starting the compressor only when the suction pressure has increased to a defrosting value and for starting the compressor at a suction pressure below the defrosting value when the valve means is operated to prevent the supply of liquid refrigerant to the second evaporator means, and "a check valve on the discharge side of the first evaporator means to prevent defrosting of the first evaporator means when the second evaporator means is defrosting. I

'7. n a control system for a refrigerating apparat having a compressor, first-and second evaporator means, a high pressure line connecting the compressor and condenser, a, liquid line connecting the condenser and the evaporator means and a suction line connecting the evaporator means and the compressor, it being desirable to defrost the second evaporator means and not the first, the combination of, valve means in the liquid line for normally allowing liquid refrigerant to be supplied to the first evaporator means but for turning on and oil the supply of liquid refrigerant to the second evaporator means, control means responsive to a temperature condition produced by the second evaporator means for operating the valve means to supply liquid refrigerant to the second evaporator means upon a call for cooling, means responsive to suction pressure and controlled by said control means upon operation of the valve means to supply liquid refrigerant to the second evaporator means for stopping operation of the compressor until the suction pressure rises to a defrosting value whereby defrosting of the second evaporator means is provided, and a check valve on the discharge side of the first evaporator means to prevent defrosting of the first evaporator means when the second evaporator means is defrosting. I

8. In a control system for a refrigerating apparatus having a compressor, first and second evaporator means, a high pressure line connecting the compressor and condenser, a liquid line connecting the condenser and the evaporator means and a suction line connecting the evaporator. means and the compressor, it being desirable to defrost the second evaporator means and not the first, the combination of, valve means in the liquid line for normally allowing liquid refrigerant to be supplied to the first evaporator means but for turning on and off the supply of liquid refrigerant to the second evaporator means, control means responsive to a temperature condition produced by the second evaporator means for operating the valve means to supply liquid refrigerant to the second evaporator means upon a call for cooling, means responsive to suction pressure and controlled by said control means upon operation of the valve means to supply liquid refrigerant to the second evaporator means for stopping operation of the compressor until the suction pressure risesto a defrosting value whereby defrosting of the second evaporator means is provided, and a check valve on the discharge side of the first evaporator means to prevent defrosting of the first evaporator means when the second evaporator means is defrosting, said suction pressure responsive means operating when the valve means is operated to prevent the supply of liquid refrigerant to the second evaporator means to start the compressor when the suction pressure increases to a value below the defrosting value.

9. In a control system for a refrigerating apparatus having evaporator means and a compressor for circulating refrigerant through the evaporator means, the combination of, first control means responsive to the suction pressure of the refrigerating apparatus for starting and stopping the compressor, and second control means responsive to a temperature condition produced by the evaporator means for controlling the first control means to determine the suction pressure value at which the compressor is started.

10. In a control system for a refrigerating apparatus having evaporator means and a compressor for circulating refrigerant through the evaporator means, the combination of, means for controlling operation of the compressor, and thermostatic means responsive to a temperature condition produced by the evaporator means for controlling said compressor controlling means to stop the compressor upon a call for cooling until the evaporator means is defrosted and ethen starting the compressor.

11. In a control system for a refrigerating apparatus having an evaporator for performing a cooling function, a thermostatic expansion valve for controlling the flow of refrigerant through the evaporator and including a temperature bulb responsive to the temperature of the refrigerant at the outlet of the evaporator and a temperature bulb responsive to the temperature of the refrigerant intermediate the inlet and outlet of the evaporator, valve means for selectively connecting the bulbs to the thermostatic expansion valve, and means responsive to a temperature condition produced by the evaporator to control the valve means for selectively placing either temperature bulb in control of the expansion valve.

12. In a refrigerating system, the combination of, a pair of evaporators connected in series, means for circulating refrigerant through the evaporators, a heater associated with the connection between the evaporators for heating the refrigerant flowing from the first evaporator to the second evaporator, and means responsive to 'the temperature of the second evaporator for nection between the evaporators for heating the refrigerant flowing from the first evaporator to the second evaporator, and means responsive to the temperature of the second evaporator and to a temperature condition produced by' the second evaporator for controlling the operation of the heater.

15. In a refrigerating system, the combination of, an evaporator formed in two serially connected sections, means for circulating refrigerant through the evaporator, an expansion valve controlling the flow of refrigerant through the evaporator, a heater located between the sections and adapted to heat the refrigerant flowing from one section to the other, a first temperature bulb responsive to the temperature of the refrigerant at the outlet of the evaporator, a second temperature bulb responsive to the temperature of the refrigerant flowing from one section to theother, means for selectively placing either temperature bulb in control of the expansion valve, and means for energizing the heater when the second temperature bulb is placed in control of the expansion valve.

16. In a refrigerating system, in combination, a plurality of evaporators, a common compressor and condenser for. supplying said evaporators with refrigerant, control apparatus for controlling the circulation of refrigerant to the evaporators to normally maintain relatively low temperatures in one evaporator and to supply effective refrigerant to another evaporator only after it has defrosted, said apparatus comprising suction pressure responsive means and an element responsive to a temperature condition produced by said other evaporator, said apparatus being operable to respond to conditions existent when said other evaporator has defrosted for causing circulation of effective refrigerant thereto, circulation of effective refrigerant to said other evaporator always being prevented when it has not defrosted, and said apparatiis embodying means controlling circulation of refrigerant to said one evaporator whether frosted or defrosted.

- trolling 17. In a refrigerating, system, in combination, a plurality of evaporators, a commoncompressor and condenser for supplying said evaporators with refrigerant, control means for controlling the circulation of refrigerant to the evapor'ators, said control means including a device responsive to suction pressure controlling the compressor, valve mechanism controlling the supply of refrigerant to one of the evaporators, and an element responsive to a temperature condition produced by said one evaporator, said element consaid valve mechanism to prevent admission of evaporating refrigerant to said one evaporator until it has defrosted.

18. In a refrigerating system, in combination,

asource of refrigerant, an evaporator coil, valve means controlling the admission of refrigerant to the coil, said valve means including means responsive to coil temperature for varying the amount of the coil effective for refrigeration, and means responsive to a portion of said coil cooperating wth saidvalve means whereby said portion is made effective for refrigeration only after it has defrosted.

19. In a refrigerating system, in combination, a source of refrigerant, an evaporator coil, valve means controlling the admission of refrigerant to the coil, said valve means including means responsive to coil temperature for varying the amount of the coil effective for refrigeration, means responsive to a portion of said coil cooperating with said valve means whereby said portion is made effective for refrigeration only after it has defrosted, and means for automatically supplying heat to said portion when it is ineffective for refrigeration.

20. In a refrigerating system, in combination, a source of refrigerant, an evaporator coil, valve means controlling the admission of refrigerant to the coil, said valve means including means responsive to coil temperature for varying the amount of the coil effective 'for refrigeration, means responsive to a portion of said coil cooperating with said valve means whereby said portion is made effective for refrigeration only after it has defrosted, said source of refrigerant comprising a compressor, a suction pressure controller for said compressor operative at predetermined pressures, and means responsive to temperature of medium cooled by said coil portion cooperating with said controller in a manner whereby said compressor is started at a higher pressure value 'when said last means calls for cooling.

JOHN L. HARRIS.