US3093977A - Control apparatus for refrigeration system - Google Patents

Description

June 18, 1963 w. w. LIEBRECHT 3,093,977

' CONTROL APPARATUS FOR REFRIGERATION SYSTEM Filed Sept. 15, 1961 THERMOSTAT S RESEg' I12 SWIT H 00 2| CONDENSER MOTOR COMPRESSOR RR NT OVERLOAD SWIT PRESSURE PUT SWITCH LOW PRESSURE OUT SWITCH 3 2 IN VEN'TOR.

Wamtmz WZIEBRECHT www ATTORNEY United States Patent 3,093,977 CONTROL APPARATUS FOR REFRIGERATION SYSTEM Waldemar W. Liehrecht, Emerson, N..l., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Filed Sept. 13, 1961, Ser. No. 137,810 4 Claims. (62-208) The present invention is concerned with tan improvement in an air conditioning control system; in particular, the improvement is in the con-trol circuit for the refrigeration apparatus to provide remote manual reset of overload or high pressure lock out.

With the popularity of air conditioning, there have been many improvements in airconditioning installations to provide more improved air conditioning. One of the problems faced with residential air conditioning is the noise of the motor compressor. To cut down the amount of noise in the home, the motor compressor and condenser with the condenser fan have often been placed outdoors. In addition, air cooled condenser systems are usually most economically installed with the compressor and high side located outdoors. When this refrigeration apparatus is outdoors exposed to colder temperatures, compressor slugging, which is a result of the migration of the refrigerant in the system to the cold compressor, may occur and causes numerous problems. One method to overcome the compressor slugging is in the use of a pump-down system which has a valve in the refrigerant line near the evaporator. The valve is controlled by a space thermostat in the home. The motor driven compressor is controlled from a low-pressure switch in the refrigeration line to maintain the pressure :on the down stream side of the compressor at some low value. When the space thermostat is satisfied, and the valve in the refrigeration line closes, the motor compressor will operate until the pressure in the suction line is reduced to the low value. Also the compressor may start at any time to maintain the low pressure which may be depleted by the valve leakage.

To control such a remote pump-down motor driven comppressor refrigeration unit with a safety circuit which is commonly known as the high impedance reset circuit, the resetting operation of the high impedance circuit can not be done directly from the space thermostat as the space thermostat does not have direct control over the energization circuit for the motor compressor control relay.

The present invention is concerned with a specific improvement to the high impedanw reset circuit to provide for remote reset whenever the circuit of the high impedance relay is momentarily broken.

An object of the present invention is to provide an improved air conditioning control circuit wherein a resetting action is obtained by a switch means which momentarily breaks a resetting circuit.

Another object of the present invention is to provide an improvement in the high impedance reset circuit when the circuit is used with a remote pump-down motor compressor unit so a resetting action of the control circuit can be obtained from a remote switch; however, the control circuit and pump-down function will not be inoperative if an open or short exists in the circuit of the remote reset switch or if the manual reset switch is left in either the open or closed position.

These and other objects of the present invention will become apparent upon the study of the following specification and drawings of which FIGURE 1 is a schematic representation of a typical air conditioning installation with the improved control circuit.

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FIGURE 2 is a portion of the complete control circuit to more clearly illustrate the operation of the present invention.

Referring to FIGURE 1, a space 10 is adapted to be air conditioned. The air from the space is circulated through an evaporator or cooling coil :11 by a fan 12 by passing into a return duct 13 and exhausting into the space by a supply duct 14. A motor 15- which is connected to a source of electrical power drives fan 12.

Mounted outside the building containing space 10 is a remote air cooled pump down motor driven refrigeration apparatus 21. The refrigeration apparatus is generally located with respect to space 10 in a manner to cut down noise which might be developed by apparatus 21. The apparatus is also generally located outdoors to most economically obtain outdoor air :for condenser cooling. A motor driven compressor 22 and a condenser coil 23 are connected to the evaporator coil to form a conventional refrigeration system, such as shown in the A. B. Newton Patent 2,214,700. The pipe connections of the refrigeration system are traced as follows: from evaporator 11, a suction pipe 23, motor compressor 22, a pipe 24, condenser coil 23, a pipe 25, a valve 30, and back to coil 11. Upon the energization of motor compressor 22, refrigerant is pumped into condenser 23, and as the heat is removed from the compressed gas by air circulating through condenser 23 under the power of fan 31, the refrigerant condenses to a liquid to flow through pipe 25 into coil 11 when valve is opened.

A relay or contactor 32 ha an energization winding 33 and a pair of normally open switches 34- and 35. Switches 34 and 35 close an energization circuit [for motor compressor 22 whenever relay 32 is energized. A conventional current overload or abnormal condition responsive switch provides an open circuit between terminals 41 and 42 whenever the current passing through the circuit of conductors 43 and 44 exceeds some predetermined value. Current overload switch 40 is connected inthe power supply circuit for compressor 22 as follows: from a source of power 4 5, a conductor 5%, switch 35, conductor 43; conductor 44, motor compressor 22, a conductor 51, switch 34, and back to the source of power through a conductor 52. Fan motor 31 is connected in parallel with motor compressor 22 to be simultaneously energized. A high pressure cutout switch 76 is connected ahead of the condenser 23 by a conduit 77. This switch provides an open circuit between terminals 78 and 79 if a pressure above some predetermined value should occur in pipe 25.

An impedance relay 53 has an energization winding 54 and a normally closed switch 55. Relay 53 is energized and locks out the motor contactor 32 upon the opening of current overload switch 4th or high refrigerant pressure limit switch 76. A momentarily open circuit or wide gap relay means '60 has an energization winding 61. Relay 61 has a switch 62 which is made up of contacts '63 and 64 and a movable member '65 moved between the two contacts upon the energization or de-energization of relay 60. While there are other forms of a wide gap or momentarily open switch means, relay 60 provides a momentarily open circuit whenever the relay means is either dc-energized or energized.

A low pressure cut-off switch 70 is connected by a pipe 71 to'suction line 23. Switch 70 provides an open circuit between terminals 72 and 73 whenever the pressure in suction line 23 reaches some predetermined low value. Low pressure cut-off switches of this type have been used to control motor compressors for a number of years. One particular switch of this type is shown in the Kronmiller Patent 2,377,503.

The energization circuit of relay 32 is traced as follows: from source of power 45, a conductor 74, terminal 72, terminal 73, a conductor St), winding 33, a terminal 81, winding 54, switch 62, and back to the source of power through a conductor 82. The connection through switch 62 is made by connecting contacts 63 and 64 together so a circuit exists either between contact 63 and member 65 or between contact 64- and member 65 depending on whether relay so is energized or de-energized, respectively. A shunt circuit made up of a series connection of switch 55, overload switch 40 and high pressure switch '76 is connected between terminal 81 and conductor 82 and can be traced by the following circuit: from terminal 81, switch 55, terminal 41, terminal 42, terminal 73, terminal 7% and back to conductor 82.

The energization circuit for valve 30 is traced as follows: from source of power 45 through conductor '74, a conductor 83, switch 84, valve 30, conductor 35, and terminal 81. Valve 30 is of a conventional solenoid type to provide an open passage in pipe to allow refrigerant to flow to coil 11 whenever the valve is en ergized.

The space or room thermostat 90 has a bimetal operated switch 91. The switch 91 is connected to control the energization of relay 92 by a circuit traced as follows: from a secondary winding 93 of a transformer 94, a conductor Q5, bimetal 1% and contact 11 which forms switch 91, conductor 162, an energization winding 103 of relay 92, conductor 1%, and back tothe source of power through conductor 165. Upon closing switch 91, energization winding 103 energizes the relay to close switch 84 so valve is energized and coil 11 is cooled to initiate the delivery of cold air to space 10. Relay 60 can be energized through a circuit traced as follows: from secondary 93, conductor 195, conductor 110, winding 61, a conductor 111, a reset switch 112 located remotely from the refrigeration apparatus 21 such as in thermostat 90, a conductor 113, conductor 95, and back to the source of power. When switch 112 is closed or opened, relay 60 is energized or de-energized, respectively, tomomentarily break switch 62 which is connected in the energization circuit of relay 53.

Referring to FIGURE 2, the control circuit for the refrigeration apparatus is shown in a more simplified manner. The circuit is readily recognized to be quite similar to the high impedance control circuit described in some detail in the Mobarry Patent 2,898,746. The high impedance circuit which is commonly known in the air conditioning field makes use of two relay windings connected in series. When a shunt circuit is removed from one of the relay windings and the two are connected in series, the current is cut down below the current needed to maintain the energization of the other or main control relay. Before the main control relay and the refrigeration apparatus can be placed back in operation, the circuit of the impedance relay must be broken and a shunt circuit re-established around the high impedance relay. Referring to FIGURE 2, winding 54 is the high impedance winding. Upon the energization of the circuit by the closing of the low pressure switch 70, the control relay or contactor 33 is energized to bring about the energization of motor compressor 22 as shown in FIGURE 1. The energization of winding 33 is accomplished through a circuit comprising the normally closed switch 55 and the overload switch and high pressure limit switch 76. Upon a call for cooling the space thermostat, switch 84 is closed to energize valve 30 which would cause an increase in the pressure of the suction line 23 to cause switch 70 to close to energize relay 33 as previously mentioned. As long as no abnormal conditions come about, the motor compressor 22 will continue to cycle to maintain the suction pressure at a level selected by switch 70, and as cooling is required in space 10, valve 30 will be opened when the thermostat calls for cooling and switch 84 is closed.

Upon the presence of an abnormal condition to open switch 40 and/or switch 76, the energization circuit of winding 33 is then transferred to the circuit made up of winding and switch 62. Winding 54 has an impedance large enough to reduce the current in this circuit to a value which would not maintain the energization of relay 32. When winding 54 is energized, switch opens so that even though the abnormal condition or overload switch 4- subsequently closes, the current level in winding 33 cannot be increased through the previously mentioned shunt circuit to bring about energization of relay 32. Not-or compressor 22 then remains de-energized until the homeowner or occupant of space 10 discovers the non-operating condition of the refrigerating apparatus. To reset the system and resore the shunt circuit so winding 33 can receive enough current to energize relay 32, switch 112 must be closed to operate switch 62. Upon the energization of relay 6%, member as shown in FIGURE 1 moves from contact 64 to contact 63; however, during this operation, the wide gap or momentarily open switch 62 breaks the energization circuit for winding 54 of relay 53 to close switch 55. Winding 33 is then energized through the shunt circuit made up of switch 55 and switches 49 and '76, and the level of current through the winding is sufficient to energize relay 32 to re-establish normal operation of the refrigeration apparatus. The resetting operation can be accomplished by opening switch 112 if it had been closed as long as switch 62 momentarily opens the energization circuit for winding 54.

In air conditioning apparatuses of this type which are used in domestic dwellings as well as other applications, the safety of the homeowners often depends on the proper operation of the apparatus; therefore, for the homeowners protection, apparatuses of this type must pass the Underwriters Laboratory requirements. One of the provisions of the Underwriters Laboratories which applies to reset circuits of this type requires that the system cannot be placed in an unsafe condition when the circuit used to provide the resetting action is either shorted or opened. Where low voltage wiring is used and the wires are not protected from mechanical damage, a shorting or breaking of the wires could possibly exist. To protect the homeowner from any condition whatever it might be which would bring about a short or open in the resetting circuit, Underwriters Laboratory requires that the safety of the circuit should not be in any way impaired by the presence of a short or open in the circuit connected to the remote reset switch 112.

By the use of the momentarily open or wide gap switch 62, the resetting operation for the high impedance reset circuit is obtained from a remote switch. By means of the momentarily open switch 62, under no condition can the circuit be held open to take the impedance relay winding 54 completely out of the circuit so that it can no longer provide the low current path for winding 33. If the wires leading to switch 112 are broken or if the switch 112 is jammed shut by the occupant, switch 62 would be closed, and upon the presence of an abnormal condition to open switch 4d, the system or refrigeration apparatus 21 would become inoperative and a serviceman would have to be called before cooling could be obtained.

The importance of the momentarily open switch 62 which can be controlled from a remote position contributes to a safety circuit for a refrigeration apparatus using the pump-down method of operation which could not be otherwise used since a normal resetting system where the sytem is reset by momentarily opening thermostat switch 91 as shown in the Mobarry patent is not possible.

While the present invention has been described as applying to one particular system, the scope of the present invention is intended to be limited by the following claims in which I claim:

1. In an air conditioning control system, an evaporator coil mounted in an air stream for delivering cooled air to a space, a remote motor compressor unit, valve means having an energization winding, means including said valve means connecting said compressor to said evaporator to form a refrigeration system to cool said evaporator when said valve is energized, a low pressure responsive switch means connected to said refrigeration system to be responsive to suction pressure of the compressor, switch means providing an open circuit when said suction pressure is reduced to said predetermined low value, a source of power, a current overload switch means for providing an open circuit when an excessive current fiows through a current responsive circuit, a control relay having an energization winding and being adapted to connect said motor compressor to said source of power through said responsive circuit, a first relay having an energization winding and a normally closed switch, a remotely controlled reset relay having a normally closed switch and a normally open switch, said relay insuring a closed circuit when said reset relay is either energized or de-energized, circuit means connecting said switch of said pressure control, said control relay energization winding, said first relay energization winding and a parallel connection of said reset switches in series to said source of power, space temperature responsive switch means, means including said space switch means for connecting said valve energization winding to said source of power where upon a call fior cooling in said space said valve is energized and said evaporator is cooled by said refrigeration system, abnormal refrigeration operating condition switch means having an open circuit when an abnormal condition is present, circuit means connecting said condition switch means and said first relay switch in a series connection in parallel with said first relay energization winding and said parallel connection of said reset switches, said reset relay switches having a wide operating gap such that said closed switch opens before said open switch closes upon energization or deenergization of said reset relay, said reset relay providing for normal operation of said control system upon an abnormal condition occurring to open said abnormal condition switch means after said first relay has become energized and said abnormal condition has disappeared to close said abnormal condition switch means.

2. A control circuit for controlling the operation of an electric motor driving a refrigeration compressor in an air conditioning installation, a source of power, first relay means having a first energization winding, means connecting said relay means to control said motor, second relay means having a second energization winding and a normally closed switch, first switch means comprising a normallyopen and a normally closed set of contacts connected in a parallel circuit, said sets of contacts being of the wide gap type so that upon operation of said switch means said parallel circuit is first momentarily open and then insuring that said parallel circuit has one set of contacts normally closed, circuit means connecting said first energization winding, said second energization winding, and said first switch means in series to said source of power, said first and second windings having impedances which limit the current in said circuit below a level required to maintain 'said first relay energized, abnormal operating condition responsive switch means providing an open circuit when an abnormal operating condition exists in the operation of said air conditioning installation, circuit means connecting said normally closed switch means and said condition responsive switch means in a second series circuit in parallel with a series circuit of Said second winding and said first switch means, said second series circuit providing a lower impedance energization circuit for said first relay means to energize said first relay means whereby upon said abnormal switch means opening said second series circuit said second relay is energized to maintain said first relay means inoperative even though said abnormal switch means subsequently closes until said first switch means is momentarily opened to close said normally closed switch.

3. A control circuit for an electric motor comprising, a source of power, first relay means having a first energizing winding, said first relay means controlling the operation of said motor, second relay means having a second energization winding and a normally closed switch, abnormal operating condition responsive switch means providing an open circuit as long as an abnormal operating condition exists, second switch means for providing a momentary open circuit and a normally closed circuit upon each operation, circuit means connecting said first energization winding, said second energization and said second switch means in a series circuit to said source of power, said series circuit having a current below the normal operating current of said first relay means, circuit means connecting said normally closed switch means and said abnormal condition responsive switch means in a shunt circuit in parallel with said second relay means and said second switch means whereby a lower resistance path is provided to increase the current in said first relay means to said normal operating current, said series circuit being connected in said circuit and energized when said shunt circuit is broken upon the presence of an abnormal condition and upon said second switch means being operated to momentarily open said series circuit after said abnormal switch means closes said low resistance circuit is again established to bring about energization of said first relay means and operation of said motor.

4. A control circuit for an electric motor comprising, a source of power, first relay means having a first energizing winding, said first relay means controlling the operation of said motor, second relay means having a second energization winding and a normally closed switch, abnormal operating condition responsive switch means proving an open circuit as long as an abnormal operating condition exists, second switch means for providing a momentary open circuit when a switch actuator is operated, circuit means connecting said first energization winding, said second energization and said second switch means in a series circuit to said source of power, said series circuit having a current below the normal operating current of said first relay means, circuit means connecting said normally closed switch means and said abnormal condition responsive switch means in a shunt circuit in parallel with said second relay means and said second switch means whereby a lower resistance path is provided to increase the current in said first relay means to said normal operating current, said series circuit being energized when said shunt circuit is broken upon the presence of an abnormal condition and upon said second switch means being operated after said abnormal switch means closes said low resistance circuit is again established to bring about operation of said motor.

References Cited in the file of this patent UNITED STATES PATENTS 2,891,386 Winter June 23, 1959 2,898,746 Mobarry Aug. 11, 1959' 2,986,018 Algren May 30, 1961 3,022,641 Myck Feb. 27, 1962

Claims (1)

1. IN AN AIR CONDITIONING CONTROL SYSTEM, AN EVAPORATOR COIL MOUNTED IN AN AIR STREAM FOR DELIVERING COOLED AIR TO A SPACE, A REMOTE MOTOR COMPRESSOR UNIT, VALVE MEANS HAVING AN ENERGIZATION WINDING, MEANS INCLUDING SAID VALVE MEANS CONNECTING SAID COMPRESSOR TO SAID EVAPORATOR TO FORM A REFRIGERATION SYSTEM TO COOL SAID EVAPORATOR WHEN SAID VALVE IS ENERGIZED, A LOW PRESSURE RESPONSIVE SWITCH MEANS CONNECTED TO SAID REFRIGERATION SYSTEM TO BE RESPONSIVE TO SUCTION PRESSURE OF THE COMPRESSOR, SWITCH MEANS PROVIDING AN OPEN CIRCUIT WHEN SAID SUCTION PRESSURE IS REDUCED TO SAID PREDETERMINED LOW VALUE, A SOURCE OF POWER, A CURRENT OVERLOAD SWITCH MEANS FOR PROVIDING AN OPEN CIRCUIT WHEN AN EXCESSIVE CURRENT FLOWS THROUGH A CURRENT RESPONSIVE CIRCUIT, A CONTROL RELAY HAVING AN ENERGIZATION WINDING AND BEING ADAPTED TO CONNECT SAID MOTOR COMPRESSOR TO SAID SOURCE OF POWER THROUGH SAID RESPONSIVE CIRCUIT, A FIRST RELAY HAVING AN ENERGIZATION WINDING AND A NORMALLY CLOSED SWITCH, A REMOTELY CONTROLLED RESET RELAY HAVING A NORMALLY CLOSED SWITCH AND A NORMALLY OPEN SWITCH, SAID RELAY INSURING A CLOSED CIRCUIT WHEN SAID RESET RELAY IS EITHER ENERGIZED OR DE-ENERGIZED, CIRCUIT MEANS CONNECTING SAID SWITCH OF SAID PRESSURE CONTROL, SAID CONTROL RELAY ENERGIZATION WINDING, SAID FIRST RELAY ENERGIZATION WINDING AND A PARALLEL CONNECTION OF SAID RESET SWITCHES IN SERIES TO SAID SOURCE OF POWER, SPACE TEMPERATURE RESPONSIVE SWITCH MEANS, MEANS INCLUDING SAID SPACE SWITCH MEANS FOR CONNECTING SAID VALVE ENERGIZATION WINDING TO SAID SOURCE OF POWER WHERE UPON A CALL FOR COOLING IN SAID SPACE SAID VALVE IS ENERGIZED AND SAID EVAPORATOR IS COOLED BY SAID REFRIGERATION SYSTEM, ABNORMAL REFRIGERATION OPERATING CONDITION SWITCH MEANS HAVING AN OPEN CIRCUIT WHEN AN ABNORMAL CONDITION IS PRESENT, CIRCUIT MEANS CONNECTING SAID CONDITION SWITCH MEANS AND SAID FIRST RELAY SWITCH IN A SERIES CONNECTION IN PARALLEL WITH SAID FIRST RELAY ENERGIZATION WINDING AND SAID PARALLEL CONNECTION OF SAID RESET SWITCHES, SAID RESET RELAY SWITCHES HAVING A WIDE OPERATING GAP SUCH THAT SAID CLOSED SWITCH OPENS BEFORE SAID OPEN SWITCH CLOSES UPON ENERGIZATION OR DEENERGIZATION OF SAID RESET RELAY, SAID RESET RELAY PROVIDING FOR NORMAL OPERATION OF SAID CONTROL SYSTEM UPON AN ABNORMAL CONDITION OCCURRING TO OPEN SAID ABNORMAL CONDITION SWITCH MEANS AFTER SAID FIRST RELAY HAS BECOME ENERGIZED AND SAID ABNORMAL CONDITION HAS DISAPPEARED TO CLOSE SAID ABNORMAL CONDITION SWITCH MEANS.

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