US2237249A - Refrigeration control system - Google Patents

Description

April 1, 194? G. H. FISHER REFRIGERATION CONTROL SYSTEM Filed Sept. 30, 1938 ihwmtov Patented Apra Tl,

PATEN T REFRKGERATKON CCQNTRQIL SYSTEM George H. Fisher, ltiinneapolis, Minn, assignor to Minneapolis-Honeywell Regulator (Company,

Minneapolis, Minn, a corporation of Delaware Application September 80, 1938, Serial No. 232,606

Claims.

This invention relates to refrigeration control systems and to improvements in the component parts thereof.

The primary object of this invention is to provide an improved control arrangement for a refrigerating apparatus which cools a plurality of fixtures or zones wherein desired temperature conditions are at all times maintained in each fixture or zone, wherein the cooling coils of all of the fixtures or zones are defrosted at each cycle of operation of the refrigerating apparatus, wherein too great a reduction of pressure on the low pressure side of the refrigerating apparatus is prevented, wherein the building up of extremely high head pressures is prevented, wherein starting of the compressor against relatively high head pressures is prevented, wherein defrosting of the coils of all of the fixtures or zones is assured at least at predetermined intervals in case the cooling load in the various fixtures or zones tends to maintain the refrigerating apparatus in continuous operation, and wherein overheating of the compressor motor is prevented by opening the energizing circuit of the compressor motor regardless of whether the overheating is occasioned by overloading of the compressor motor or by the occurrence of a decrease in potential difference across the energizing circuit of the compressor motor, the arrangement being such that if the energizing circuit is opened by an overload condition manual reclosing is required but if it is opened by a decrease in potential difference it is reclosed automatically.

Further objects of the invention are to provide novel control arrangements forming parts of the improved complete control arrangement outlined above.

For a more thorough understanding of this invention reference is made to the accompanying drawing in which:

Figure l is a diagrammatic illustration of the complete control system of this invention as applied to a multiple fixture or zone refrigerating apparatus,

Figures 2 and 3 are partial views showing the overload cut-out mechanism of Figure 1 in various operative positions.

Referring now to Figure 1 a plurality of fixtures or zones to be cooled are illustrated at H], H, and I2. rooms, walk-in boxes, show counters, or any other type of device which it be desired to cool. The fixtures or zones 10, II, and [2 are provided with cooling coils 13, It, and 15 preferably in the form of evaporators for cooling the same. Refrigerant These fixtures or zones may be is supplied to and withdrawn from the evaporators 53, i i, and i5 by means of a refrigerating apparatus generally designated at l E. The refrigerating apparatus may comprise a compressor ll operated by an electric motor 8 8. Compressed refrigerant leaves the compressor ll through a high pressure line 119 and flows into a condenser 26 wherein it is condensed. Condensed refrigerant is collected in a receiver 2i and then flows through a liquid line 22 and branch liquid lines 23, 2 5, and 25 into the evaporators i3, M, and i5, respectively. Expanded refrigerant is Withdrawn from the evaporators i3, i l, and 55 through a low pressure or suction line 26 by the compressor El. It is here noted that the evaporators it, i l, and 95 are arranged in parallel relationship. Expansion valves 27, 28, and 29 control the supply of refrigerant flowing to the evaporators it, Hi, and 15, respectively, and these expansion valves may be of the thermostatic type provided with a bulb located at the discharge of the evaporators and connected by a capillary tube 38 to the expansion valves. Since the construction outlined above is generally old in the art a further description of the above is not considered necessary.

Located in the branch liquid lines 23, 26, and 25 are solenoid valves 35, 36, and 37 for turning on or turning oil the supply of refrigerant to the evaporators l3, M, and 95, respectively. When the solenoid valves 35, 36, and 31 are energized, refrigerant is supplied to their associated evaporators and when the solenoid valves are deenergizedfthe supply of refrigerant to their associated evaporators is shut off. The zones or fixtures If], H, and 12 are provided with temperature responsive control means in the form of thermostats 38, 39, and it, respectively. The thermostat 38 may comprise a bellows 52 charged with a volatile fluid for operating a lever 43 against the action of an adjustable tension spring 44. The lever 43 operates a mercury switch 45 provided with electrodes 46, M, and 48. For purposes of illustration it is assumed that when the temperature within the fixture ll] rises to 42, the switch 45 is tilted to a position to bridge the electrodes as, M, and [i8 and when the temperature decreases to the switch is tilted to the position shown to unbridge the electrodes. The construction and operation of the thermostats 39 and 40 are exactly the same as that of thermostat 38 and consequently like reference characters for like parts have been utilized.-

A relay or starter for the compressor motor [8 is generally designated at and may comprise an operating coil 5! for operating switch arms 52 and 53 with respect to stationary contacts 56 and 55. The arrangement is such that when the operating coil 5i is energized the switch arms 52 and 53 move into engagement with their respective contacts 55 and 55 and when the operating coil 5| is deenergized the switch arms 52 and 53 are moved out of engagement with their respective contacts by means of springs, gravity or other means (not shown).

The thermostats 38, 39, and 60 in addition to controlling the energization of their associated solenoid valves 35, 36, and 31 also control the operation of the relay 0r starter 50 and hence the operation of the compressor ll. The relay or starter 50 is also controlled by control means 51 and 58 responsive to the pressure on the high pressure side of the refrigerating apparatus, by control means 59 and 60 responsive to the pressure on the low pressure side of the refrigerating apparatus, by an overload cut-out mechanism 6| responsive to the current flow in the energizing circuit of the compressor motor I8 and by a timer generally designated at 62.

The control means 51 responsive to pressure on the high pressure side of the refrigerating apparatus may comprise a bellows 65 connected by a pipe 66 to the high pressure line IQ for operating a lever 61 against the action of an adjustable tension spring 68. The lever 51 operates a mercury switch 89 the parts being so arranged that the switch 69 is moved to closed position when the pressure on the high pressure side of the refrigerating apparatus decreases to 140 pounds and moves to open position when the pressure increases to 145 pounds. The control means 51 operates to determine at what pressure on the high pressure side of the refrigerating apparatus the compressor motor l8 may be placed in operation.

The control means 58 may comprise a bellows 10 connected by the pipe 66 to the high pressure line IQ for operating a lever ll against the action of an adjustable tension spring I2. The lever 1| operates a mercury switch 13, the parts being so arranged that the switch I3 is moved to open position when the pressure on the high pressure side of the refrigeratin apparatus rises to 200 pounds and to closed position when the pressure decreases to 195 pounds. The control means 58 determines at what pressure on the high pressure side of the refrigerating apparatus that the compressor motor !8 is stopped.

The control means 59 may comprise a bellows U3 connected by a pipe to the low pressure or suction line 26 for operating a lever 16 against the action of an adjustable tension spring 11. The lever 16 operates a mercury switch 18 to close the switch when the pressure on the low pressure side of the refrigerating apparatus rises to 38 lbs. and to open the switch when the pressure decreases to 33 lbs, For purposes of illustration it is assumed that the pressure on the low pressure side of the refrigerating apparatus rises to 38 pounds only after defrosting of all of the evaporators I3, l6, and I5 has occurred. The control means 59 operates to prevent operation of the compressor motor 3 until the pressure on the low pressure side of the 'refrigerating apparatus has risen to a value indicating that defrosting of all of the evaporators has occurred.

The control means 60 may comprise a bellows 19 connected by the pipe 15 to the low pressure or suction line for operating a lever 80 against the action of an adjustable tension sprin The lever operates a mercuryswitch 82, the parts being so arranged that the switch 82 is moved to open position when the pressure on the low pressure side of the refrigerating apparatus decreases to 10 lbs, and is moved to closed position when the pressure increases to 15 lbs. The control means 80 determines the pressure on the low pressure side of the refrigerating apparatus at which the compressor motor I8 is stopped.

The overload cut-out mechanism 8i comprises a movable contact 85 and a stationary contact 88 which are in engagement during normal operation of the refrigerating apparatus. occurrence of an overload condition the contacts 85 and 86 are separated in a mannerto be pointed out more fully hereafter.

The timer generally designated at 62 may comprise a rotor 88 operated by a field winding 89 connected across line wires I00 and I0! leading from some source of power (not shown). The

rotor 88 operates a cam 9| through a reduction" gear train 90, the cam 9! being provided with a high dwell for operating a lever 92 which in turn operates a mercury switch 93. For purposes of illustration it is assumed that the parts are so arranged that the mercury switch 93 is moved to open position for a short interval of time every six hours.

Assume now that the temperature within the fixture or zone I0 rises to 42 whereupon the switch as is tilted to a position to bridge the electrodes 66, ll, and 68; a circuit is thereupon completed from the line wire I00 through wire I02, electrodes 46 and 48, wire I03, solenoid valve 35 and wire I08 back to the other line wire I01. Completion of this circuit energizes the solenoid valve 35 to supply refrigerant to the evaporator l3 within the fixture or zone Hi. When the temperature within the fixture or zone It decreases to 40 to open the switch t5 the solenoid valve 35 is deenergized to shut off the supply of refrigerant to the evaporator l3. In this manner the solenoid valve 35 is operated to maintain desired temperatures within the fixture or zone ill. The thermostat 39 and solenoid valve 36 are connected together and to the line wires I00 and lill in exactly the same manner as the thermostat 38 and solenoid valve'35 and accordingly like reference characters primed have been utilized for like connections. Also the thermostat 38 and the solenoid valve 3'? operate in the same manner and accordingly the wiring connections have been designated by like reference characters double primed. Summing up, when any thermostat in any of the fixtures or zones calls for cooling, its associated solenoid valve is opened to supply refrigerant to its associated evaporator to maintain desired temperatures in all of the fixtures or zones,

Assume now that the high pressure decreases to lbs. whereupon the switches 59 and 13 of the control means.51 and 58 are closed, that the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value of 38 lbs. whereupon the switches 18 and 82 of the control means 59 and 60 are closed, and that the temperature within the fixture or zone In rises to 42 to close the switch 45. A circuit is thereupon completed from the line wire I00 through wire I02, electrodes 46 and 41, wires I06, I07, and I08, mercury switch 93, wires I09 and H0, mercury switch 69, wire Ill, mercury switch 78, wires H2 and H3, contacts 86 and 85 of the overload cut-out mechanism 8|, wire H4, operating coil 5|, and wire H5 back to the other line Upon the wire ll. Completion of this starting circuit energizes the operating coil 5i to move the switch arms 52 and 53 into engagement with their respective contacts 54 and 55.

Movement of the switch arm 53 into engagement with the contact 55 completes an energizing circuit for the compressor motor i8 which may be traced from the line wire I08 through wires H8, H9, and I20, heater l2I, wire I22, switch arm 53, contact 55, wire I23, compressor motor I 8, and wires I24 and I25 back to the other line wire IOI. Accordingly when the operating coil M is energized the compressor motor I8 and hence the refrigerating apparatus is in operation.

Movement of the switch arm 52 into engagement with the contact 54 completes a maintaining circuit for the operating coil 5| of the relay or starter 50 which is independent of the switches 89 and I8 of the control means 5! and 59,, respectively. This maintaining circuit may be traced from the line wire I through wire I02, electrodes 46 and 41 of the thermostat 38, wires I 08, I01, and I08, mercury switch 93, wires I09 and I28, mercury switch I3, wire I29, mercury switch 82, wire I30, contact 54, switch arm 52, wire H3, contacts 86 and 85, wire I I4, operating coil i, and wire I I5 back to the other line wire I0l. Completion of this-circuit maintains the operating coil 5I energized until any of the switches 45, I3, 82, or 93-are opened, or until the contacts 85 and 88 of the overload cut-out mechanism 6I.are separated. The electrodes 46 and 47 of the switches 45 of the thermostats 39 and 40 are connected in parallel with the electrodes 46 and 4! 'of the thermostat 38, these parallel connections being shown by I02 and I06 for the thermostat 39 andl02" and I06 for the thermostat 40.

, Summing up two circuits are provided for controlling the energization of the operating coil 5|, a starting circuit including the switches 45 of the thermostats 38, 39, and 40 connected in parallel, the switch 93 of the timer 62, the switches 69 and I8 of the control means 51 and 59 and the contacts 85 and 86 of the overload cut-out 6|. The other circuit is a maintaining circuit which includes the switches '45 'of the thermostats 38, 39, and 40 connected in parallel, switch 93 of the timer 62, the switches 13 and 82 of the controLmeans 58 and 60, the maintaining switch formed by the switch arm 52 and contact 54 of the relay or starter 50, and the contacts 85 and 85 of the overload cut-out mechanism 6|. The operating coil 5| of the relay maybe energized and hence the relay pulled inonly when the starting circuit is completed and it is maintained energized, after it has once been energized by the starting kcircuit, so long as the maintaining circuit is completed. Accordingly, the operating coil 5| .of the relay or starter may be energized to operate the compressor I! only when any of the thermostats 38, 39, and 40 are calling for cooling, the timer switch 93 is closed, the pressure on the high pressure side of the refrigerating apparatus has decreased to 140 pounds to close the switch 68, the pressure on the low pressure side of the refrigerating apparatus has risen to a defrosting value of 38 lbs. to close the switch I8,and the contacts 85 and 86 of the overload cut-out BI are closed. Hence the refrigerating apparatus can only be started after defrosting of all of the evaporators has taken place and when the pressure on the high pressure side of the refrigerating apparatus has reduced to a predetermined low value which greatly reduces the starting load on the compressor motor I8 and hence eliminates the majority of the starting overload conditions.

After the compressor I? has been placed in operation in the manner pointed out above, it will remain in operation until either all of the thermostats 33, 39, and 00 are satisfied, or the switch 93 of the timer 62 is opened, or the pressure on the high pressure side of the refrigerating apparatus rises to 200 lbs. to open the switch I3, or the pressure on the low pressure side of the refrigerating apparatus decreases to 10 lbs. to open", the switch 82, or the contacts and 88 separate upon the occurrence of an excess current fiow in the energizing circuit of the compressor motor.

The system thus far described controls the operation of the refrigerating apparatus to maintain at all times desired temperature conditions in the various fixtures or zones I0, II, and I2, to provide defrosting of all of the evaporators 53, I4, and I5 at each cycle of operation of the compressor IT, to prevent too great a reduction of pressure on the low pressure side of the refrigerating apparatus, to prevent thebuilding up of extremely high pressures on the high pressure side of the refrigerating apparatus and to prevent starting of the compressor against relatively high head pressures. Ordinarily thermostats 38, 38, and 48 will tend to call for cooling at substantially the same times and will tend to be satisfied at substantially the same times so that intermittent defrosting of the evaporators I 3, I4, and I5 will occur. However, it is quite possible under certain operating conditions that at least one of the thermostats 38, 39, and 40 will be calling for cooling at the same time and after the compressor is placed in operation it will remain in operation for a long period of time tending to build up frost on the evaporators I3, I4, and I5. The timer operating the switch 93 is utilized for shutting down the refrigerating apparatus at predetermined times, say every six hours, and after the refrigerating apparatus has been shut down in this manner it is impossible to restart the same until the suction pressure has risen to the defrosting value of 38 lbs. Accordingly defrosting of the evaporators -I3, I4, and I5 at least every six hours is provided. In other words, the timer 62 operates to insure that the evaporators I3, I4 and I5 will be defrosted at least at predetermined times although the evaporators are usually defrosted more often than this.

The overload cut-out mechanism BI may comprise a support I32 carrying a pivot I33. A lever I34 is carried by the pivot I33 and is urged downwardly by a spring I35 into engagement with the end of a bimetallic element I36 also secured to the support I 32. Levers I31 and I38 are fulcrumed on the support I32 and are connected together by an overcenter spring I39. The lever I31 carries an insulating pad I40 upon which are mounted the movable contact 85 and a movable contact I4I which is adapted to engage a stationary contact I42. The lever I34 is provided with a slot I43 for receiving the end of the lever I38. With the parts in the position shown in Figure l, the lever I34 is engaging the bimetallic element I36 and the overcenter spring I 39 holds the movable contact 85 in engagement with the stationary contact 86. If now the current flow in the energizing circuit for the compressor motor I8 should become excessive, the heater element I2I will heat the bimetallic element I35 and warp the same outwardly to the position shown in Figure 2. Outward movement of the bimetallic element I36 releases the lever I34 and the spring I35 moves the same downwardly. Downward movement of the lever 1313 causes the lever I38 to move downwardly to move the spring I39 overcenter, which in turn causes the contacts 85 and 85 to separate with a snap action and causes contacts IQI and I 32 to make with a snap action. Separation of the contacts 85 and 86 in this manner interrupts the above outlined starting and maintaining circuits for the operating coil I to drop out the relay or starter 5'0 and stop operation of the compressor motor I8.

An auxiliary lever MB is secured to the main lever I31 by a pivot M1, the auxiliary lever being maintained normally in the position shown in Figures 1 and 2 by a compression spring M8. The lever I M5 is provided with an extension I419 which is adapted to be engaged by an abutment I56 which is secured to a button I5I. A compression spring I52 located between the button I5I and a stationary support I53 maintains the abutment I50 in the position shown in Figures 1, 2, and 3. After the overload cut-out mechanism 61 separates the contacts 85 and 85 in the manner outlined above, the overload cut-out mechanism may be restored to the position shown in Figure 1 by pressing inwardly on the button I5I. This raises the lever I34 about its pivot I33 and allows the bimetallic element I36 to again move under the lever I3 1 to hold the parts in the position shown in Figure l.

A stationary contact I55 is secured to a suitable support I58 and a movable contact I51 is secured to a support I58. An armature I59 is secured to the movable contact I51 and is influenced by a winding I60, connected by wires ISI and I52 across line wires I00 and IGI. When the potential difference across the line wires IE1! and IQI is at a predetermined value the winding I50 maintains the solenoid I59 and the movable contact I51 in the position shown in Figure 1. If the potential difierence across the line wires Iii!) and H11 should decrease to a predetermined low value, then the armature I59 and the contact I51 move downwardly as shown in Figure 3 under the influence of springs, gravity or other means (not shown) to cause the movable contact I51 to engage the stationary contact I55. An abutment surface I53 formed on the lever I65 prevents downward movement of the movable con.- tact I51 if the potential difierence across the line wires I00 and IIII decreases after the overload cut-out mechanismhas been operated to separate the contacts 85 and 85 as is clearly illustrated in Figure 2.

A bimetallc element I65 carried by the support I56 is adapted to engage a lug I51 carried by the lever I34, the bimetallic element I65 being heated by a heater I66. The energization of the heater I66 is controlled by a relay I which may comprise an operating coil H! for moving switch arms I12 and I13 into engagement with contacts 114 and I15, respectively, when energized. When the operating coil I1I is deenergized the switch arms I12 and I13 are moved out of engagement with their respective contacts by means of springs, gravity or other means (not shown).

Assume now that the parts are in the position shown in Figure 1 and that the potential difference across the line wires I00 and Illl decreases to a predetermined value to cause the movable contact I01 to engage the stationary contact I55. If this decrease in potential difference persists the current flow through the heater IZI will increase to cause outward flexing of the bimetallic element I35 to separate the contacts 85 and 86 and to close the contacts MI and I42, this movement being permitted by the pivotal connection I441 between the levers I34 and H16 and the spring I118 as shown in Figure 3. Separating of the contacts 85 and 86 stops operation of the compressor motor I8 and movement of the contact I 31 into engagement with the contact M2 completes a circuit from the line wire I00, through wire I18, contacts I51 and I55, wires I19 and I86, operating coil I11, wire IBI, contacts MI and M2, and wires I82 and I25 back to the other line wire IIlI. Completion of this circuit causes energization of the operating coil Hi to move the switch arms I12 and 113 into engagement with their respective contacts.

Movement of the switch arm I12 into engagement with the contact I14 completes a maintaining circuit for the operating coil I1I which may be traced. from the line wire I00 through wires I13 and I26, switch arm I12, contact I1 1, wires I211 and 1311, operating coil I11, wire IBI, contacts MI and M2, and wires I82 and I25 back to the other line wire IEII. This maintaining circuit maintains the operating coil I'II energized until such time as the contacts MI and M2 are separated. Movement of the switch arm I13 into engagement with contact 115 completes a circuit from the line wire 1% through wires H8, 119, and I83, switch arm I13, contact I15, wire I81, heater I65, and wire I back to the other line wire I131. Ccmpletion of this circuit energizes the heater element I66 which flexes the bimetallic element I65 upwardly to move the lever I36 upwardly which in turn separates the contacts MI and M2 and recloses the contacts 55 and 86.

From the above it is seen that the overload cut-out mechanism SI operates to separate the contacts 25 and 8% to stop operation of the compressor when the current flow in the energizing circuit of the compressor motor becomes excessive. If the excessive current flow in the energizing circuit for the compressor motor is caused by a decrease in potential difference across the power lines, the contacts and at will be reclosed automatically after they have once been opened, the length of time required for automatically reclosing the contacts 35 and being determined by the length of time required for the bimetallic element I65 to move the lever I36 upwardly. If the excessive current flow in the energizing circuit of the compressor motor should be caused by something other than a decrease in potential difierence,'the contacts 85 and 35 are separated to stop operation of the compressor motor and they may be reclosed only by manual manipulation of the button I 5I. Automatic reclosing under these conditions is prevented by the abutment surface I63 on the lever I 15.

Since most of the overload conditions in a refrigerating apparatus are caused by starting the compressor against relatively high head pressures or by continuing the compressor in operation when the head pressure becomes extremely high or the suction pressure becomes extremely low, the complete system outlined above obviates most of these conditions so that the compressor motor I8 will seldom if ever become overloaded. The other condition which causes excessive current flow through the compressor motor is usually a decrease in potential difference across the energizing circuit and since this is not a very serious condition it is desirable to automatically reclose the overload cut-out mechanism when the overload cut-out mechanism is opened by this condition. If an overload condition other than those outlined above should occur this would be an indication that something was radically wrong with the refrigerating system and when the overload cut-out mechanism 6| stops operation of the compressor motor due to these other conditions,-manual resetting of the overload cut-out mechanism BI is required. This will indicate that the system should be checked for faulty operation.

From the above it is seen that this invention contemplates a complete system for maintaining accurate temperature conditions in a plurality of fixtures or zones, for defrosting the evaporators at each cycle of operation of the refrigerating apparatus, for insuring that the evaporators will defrost at least once during a predetermined time interval and for providing safe operation of the system. In this latter respect the existence of extremely high pressures on the high pressure side of the refrigerating apparatus and extremely low pressures on the low pressure side of the apparatus are prevented as well as overheating of the compressor motor.

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

I claim as my invention:

1. In a control system for a refrigerating apparatus .having a compressor and evaporator means associated therewith for cooling a medi um, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, a first control device including a first switch and means responsive to pressure on the high pressure side of the refrigerating apparatus for closing and opening the first switch as the pressure respectively falls below or rises above a predetermined low pressure value, a second control device including a second switch and means responsive to pressure on the high pressure side of the refrigerating apparatus for closing and opening the second switch as the pressure respectively falls below or rises above a predetermined high pressure value,

a third control device including a third switch and means responsive to the pressure on the low pressure-side of the refrigerating apparatus for closing and opening the third switch as the pressure respectively rises above or falls below a predetermined high value, a fourth control device only the maintaining switch and the second and fourth switches for maintaining the relay energized when the maintaining switch and the second and fourth switches are closed whereby the compressor is maintained in operation until the pressure on the high pressure side of the refrigerating apparatus rises above the predetermined high value or until the pressure on the low pressure side of the refrigerator apparatus falls below the predetermined low value.

2. In a control system for a refrigerating apparatus having a compressor. and evaporator means associated therewith for cooling a medi= um, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, a first control device including a first switch and means responsive to pressure on the high pressure side of the refrigerating apparatus for closing and opening the first switch as the pressure respectively falls below or rises above a predetermined low pressure value, a second control device including a second switch and means responsive to pressure on the high pressure side of the refrigerating apparatus for closing and opening the second switch as the pressure respectively falls below or rises above a predetermined. high pressure value, a third control device including a third switch and means responsive to the pressure on the low pressure side of the refrigerating apparatus for closing and opening the third switch as the pressure respectively rises above or falls below a predetermined high value, a fourth control device including a fourth switch and means responsive to the pressure on the low pressure of the re including a fourth switch and means responsive to the pressure on the low pressure .of the refrigerating apparatus for closing and opening the fourth switch as the pressure respectively rises above or falls below a predetermined low value. a starting circuit for the electrically operated relay including only the first and third switches for energizing the relay when both the first and third switches are closed whereby the compressor is started when the pressure on the high pressure side of the refrigerating apparatus falls below the predetermined low value and the pressure on the low pressure side rises above the pre- ,a

determined high value, and a maintaining circuit for the electrically operated relay including frigerating apparatus for closing and opening the fourth switch as the pressure respectively rises above or falls below a predetermined low value, a fifth control device including a fifth .switch and means responsive to the temperature of the medium being cooled for closing and open- I ing the fifth switch as the temperature respectively rises above or falls below a predetermined value, a starting circuit for the electrically operated relay including only the first, third and fifth switches for energizing/the relay only when the first, third and fifth switches are closed, and a maintaining circuit for the electrically operated relay including only the maintaining switch and the second, fourth and fifth switches for maintaining the relay energized until either the second, fourth or fifth switches are opened.

3. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, control means responsive to the pressure on the low pressure side of the refrigerating apparatus, means controlled by the control means and the thermostatic control means for starting operation of the compressor only when any of the thermostatic control means calls for cooling and the pressureon the low pressure side of the refrigerating apparatus rises to a defrosting value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

4. In a control system 'for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, control means responsive to the pressure on the low pressure side of the refrigerating apparatus, means associated with each zone and controlled by the thermostatic control means of that zone to admit refrigerant to the evaporator of that zone upon a call for cooling by the thermostatic control means of that zone, means controlled by the control means and the thermostatic control means for starting operation of the compressor only when any of the thermostatic control means calls for cooling and the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to a predetermined low value, and means operatively associated with said last mentioned means for stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

5. In a control-system for a refrigerating apparatus having a compressor and a plurality of evaporators for coolng medium in a plurality of zones, the combination of, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, control means responsive to the pressure on the low pressure side of the refrigerating apparatus, control means responsive to the pressure on the high pressure side of the refrigerating apparatus,

' means controlled by both of the control means and the thermostatic control means for starting operation of the compressor only when any of the thermostatic control means call for cooling, the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predertermined low value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the prespressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value, and means associated with said last mentioned means for stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

7. In a control system for a refrigerating apparatus having a compressor and a plurality'of evaporators for cooling medium in a plurality of zones, the combination of, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, means associated with each zone and controlled by the thermostatic control means of that zone to admit refrigerant to the evaporator of that zone upon a call for cooling by the thermostatic control means of that zone, control means responsive to the pressure on the low pressure side of the refrigerating apparatus, control means responsive to the pressure on the high pressure side of the refrigerating apparatus, means controlled by both of the control means and the thermostatic control means for starting operation of the compressor only when any of the thermostatic control means call for cooling, the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value, and means associated with said last mentioned means for stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

8. In a control system for a refrigerating apparatus having a compressor and a plurality of sure on the high pressure side of the refrigerating apparatus increases to a predetermined high value, and means associated with said last mentioned means for stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

6. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, thermostatic control' means for each zone responsive to the temperature of the medium being cooled of that zone,

control means responsive to the pressure on the low pressure side of the refrigerating apparatus,

control means responsive to the pressure on the operation of the compressor only when any of the thermostatic control means call for cooling, the

7 'high pressure side of the refrigerating apparatus, I means controlled by both of the control means and the thermostatic control'means for starting evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when en-. ergized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call'for cooling, a first switch, means responsive to the pressure on the low pressure side of the refrigerating apparatus for closing the first switch when the pres-' sure rises above a defrosting value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first switch arranged in series with the thermostatic'ally operated switch means for energizing the relay only when any of the thermostatically operated switch means are closed and the first switch is closed whereby the compressor is started only when at least one of the thermostatically operated switch means is calling for cooling and the pressure on the low pressure side of the refrigerating apparatus has risen to a defrosting value, a maintaining circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the maintaining switch for maintaining the relay energized and the compressor in operation until all of the thermostatically operated switch means are satisfied, a normally closed time operated switch opened at predetermined times, said time operated switch being located in series with said thermostatically operated switch means for deenergizing the electrically operated relay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined tims.

9. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call for cooling, first and second switches, means responsive to pressure on the low pressure side of the refrigerating apparatus for closing the first switch when the pressure rises to a defrosting value and for opening the second switch when the pressure decreases to a predetermined low value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first switch arranged in series with the thermostatically operated switch means for energizing the relay only when any of th thermostatically operated switch means are closed and the first switch is closed whereby the compressor is started only when at least one of the thermostatically operated switch means is calling for cooling and the pressure on the low pressure side of the refrigerating apparatus has risen to a defrosting value, a maintaining circuit for the electrically operated relay including the maintaining switch, the thermostatically operated switch means arranged in parallel with respect to each other and the second switch for maintaining the relay energized and the compressor in operation until either all of the thermostatically operated switch means are satisfied or until the pressure on the low pressure side of the refrigerating apparatus decreases to the predetermined low value to open the second switch, a normally closed time operated switch opened at predetermined times, said time operated switch being located in series with the thermostatically operated switch means for deenergizing the electrically operated relay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times.

10.In a control system for refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call for cooling, first and second switches, means responsive to prescreases to a predetermined low value and for opening the fourth switch when the pressure increases to a predetermined high value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first and third switches for energizing the relay only when any of the thermostatically operated switch means are. closed and the first and third switches are closed whereby the compressor is started only when at least one of the thermostatically operated switch means are calling for cooling, the pressure on the low pressure side of the refrigerating apparatus has risen to the defrosting value and the pressure on the high pressure side of the refrigerating apparatus has decreased to the predetermined low value, a maintaining circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other, the maintaining switch and the second and fourth switches for maintaining the relay energized and the compressor in operation until either all of the thermostatically operated switch means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to the predetermined low value to open the second switch or the pressure on the high pressure side of the refrigerating apparatus increases to the predetermined high value to open the fourth switch, a normally closed time operated switch opened at predetermined times, said time operated switch being located in series with said thermostatically operated switch means for deenergizing the electrically operated relay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times.

11. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call for cooling, means associated with each zone and controlled by the thermostatically operated switch means of that zone to admit refrigerant to the evaporator of that zone upon a call for cooling by the thermostatically operated switch means of that zone, a first switch, means responsive to the pressure on the low pressure side of the refrigerating apparatus for closing the first switch when the pressure rises above a defrosting value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first switch arranged in series with the thermostatically operated switch means for energizing the relay only when any of the thermostatically operated switch means are closed and the first switch is closed whereby the compressor is started only when at least one of the thermostatically operated switch means is calling for opened at predetermined times, said time operated switch being located in series with said thermostatically operated switch means for deenergizing the electrically operated relay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times,

12. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call for cooling, means associated with each zone and controlled by the thermostatically operated switch means of that zone to admit refrigerant to the evaporator of that zone upon a call for cooling by the thermostatically operated switch means of that zone, first and second switches, means responsive to pressure on the low pressure side of the refrigerating apparatus for closing the first switch when the pressure rises to a defrosting value and for opening the second switch when the pressure decreases to a predetermined low value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first switch arranged in series with the thermostatically operated switch means for energizing the relay only when any of the thermostatically operated switch means are closed and the first switch is closed whereby the compressor is started only when at least one of the thermostatically operated switch means is calling for cooling and the pressure on the low pressure side of the refrigerating apparatus has risen to a defrosting value, a maintaining circuit for the electrically operated relay including the maintaining switch, the thermostatically operated switch means arranged in parallel with respect to each other and the second switch for maintaining the relay energized and the compressor in operation until either all of the thermostatically operated switch means are satisfied or until the pressure on the low pressure side of the refrigerating apparatus decreases to the predetermined low value to open the second switch, a normally closed time operated switch opened at predetermined times, said time operated switch being located in series with the thermostatically operated switch means for deenergizing the electrically operatedrelay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times.

13. In a control system for a refrigerating apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, an electrically operated relay for operating the compressor when energized and including a maintaining switch closed upon energization of the relay, thermostatically operated switch means for each zone responsive to the temperature of the medium being cooled of that zone and closed upon a call for cooling, means associated with each zone and controlled by the thermostatically, operated switch means of that zone to admit refrigerant to the evaporator of that zone upon a call for cooling by the thermostatically operated switch means of that zone, first and second switches, means responsive to pressure on the low pressure side of the refrigerating apparatus for closing the first switch when the pressure rises to a defrosting value and for opening the second switch when the pressure decreases to a predetermined low value, third and fourth switches, means responsive to pressure on the high pressure side of the refrigerating apparatus for closing the third switch when the pressure decreases to a predetermined low value and for opening the fourth switch when the pressure increases to a predetermined high value, a starting circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other and the first and third switches for energizing the relay only when any of the thermostatically operated switch means are closed and the first and third switches are closed whereby the compressor is started only when at least one of the thermostatically operated switch means are calling for cooling, the pressure .on the low pressure side of the refrigerating apparatus has risen to the defrosting value and the pressure on the high pressure side a of the refrigerating apparatus has decreased to the predetermined low value, a maintaining circuit for the electrically operated relay including the thermostatically operated switch means arranged in parallel with respect to each other, the maintaining switch and the second and fourth switches for maintaining the relay ener gized and the compressor in operation until either all of the thermostatically operated switch means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to the predetermined low value to open the second switch or the pressure on the high pressure side of the refrigerating apparatus increases to the predetermined high value'to open the fourth switch, a normally closed time operated switch opened at predetermined times, said time operated switch being located in series with said thermostatically operated switch means for deenergizing the electrically operated relay and stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times.

14. In a control system for a refrigerating apparatus having an electrically operated compressor and a plurality of evaporator means for cooling medium in a plurality of zones, the combination of, an energizing circuit for the electrically operated compressor, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, controlv means responsive to the pressure on the high pressure side of the refrigerating apparatus, control means responsive to thepressure on the low pressure side of the refrigerating apparatus, switch means controlled by the control means and the thermostatic control means for controlling the energizing circuit to start the compressor only when any of the thermostatic control means calls for cooling, the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and the pressure on the high pressure side of the refrigerating apparatus decreases to a predetermined low value and for continuing the compressor in operation until either all of the thermostatic control means are satisfied or the pressure on the low pressure side of the refrigerating apparatus decreases to a predetermined low value or the pressure on the high pressure side of the refrigerating apparatus increases to a predetermined high value, means associated with said switch means for opening the energizing circuit for stopping operation of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to the defrosting value at least at these predetermined times, overload means associated with said switch means and responsive to current flow in the energizing circuit for opening the energizing circuit upon the occurrence of excessive current flow, means for manually operating the overload means for reclosing the energizing circuit, and means responsive to the potential difference across the energizing circuit and operative upon opening of the energizing circuit for automatically operating the overload means to reclose automatically the energizing circuit when the same has been opened by an excessive current flow in theenergizing circuit caused by a decrease in potential diiference across the energizing circuit.

15. In a control system for a refrigeration apparatus having a compressor and a plurality of evaporators for cooling medium in a plurality of zones, the combination of, thermostatic control means for each zone responsive to the temperature of the medium being cooled of that zone, control means responsive to the pressure on the low pressure side of the refrigerating apparatus, means controlled by the control means and the thermostatic control means for starting operation of the compressor only when any of the thermostatic control means calls for cooling and the pressure on the low pressure side of the refrigerating apparatus rises to a defrosting value and for continuing the compressor in operation until all of the thermostatic control means are satisfied, and means operatively associated with said last mentioned means for stopping operation .of the compressor at predetermined times whereby the pressure on the low pressure side of the refrigerating apparatus will rise to a defrosting value at least at these predetermined times.

' GEORGE H. FISHER.

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