Control Circuit For An Air Conditioning System

Abstract

An air conditioning system is provided to supply treated air to an area. The system includes a refrigeration unit comprising a motor-driven compressor, a condenser, an evaporator, and expansion means. The motor includes a run winding and a start winding connected in parallel. The start winding has a positive temperature coefficient thermistor connected in series therewith to interrupt operation of the start winding after the motor has reached its operating speed. A bimetallic switch responsive to the temperature of the thermistor is actuated thereby. During normal operation, a bypass circuit about the bimetallic switch prevents the switch from having any effect on the operation of the compressor motor. When the compressor motor is deenergized, the bypass becomes ineffective. The switch, which has been opened by the temperature of the thermistor, prevents reenergization of the compressor motor until a predetermined period of time has elapsed.

Description

BACKGROUND OF THE INVENTION

The utilization of split-phase induction motors to drive the compressors of refrigeration units has become increasingly prevalent. Such a refrigeration unit, including the compressor, condenser, evaporator, and expansion means, is typically employed in an air conditioning system, such as a room air conditioner.

A split-phase motor is a single-phase induction motor equipped with an auxiliary winding displaced in magnetic position from, and connected in parallel with, the main winding. When the motor has attained a predetermined speed, the circuit to the auxiliary winding is opened. The means to open the auxiliary circuit have generally included mechanically operated devices, such as centrifugal switches. However, it has been proposed that a temperature sensitive resistance element, such as a positive temperature coefficient thermistor, be used in series with the auxiliary winding. The self-heating effect of the thermistor operates to interrupt substantially all flow of current to the auxiliary winding to effectively remove same from operation once starting of the compressor motor has been obtained.

The utilization of split-phase motors is limited to applications where low starting torque is required. In the conventional air conditioning system refrigeration unit, when the electrical circuit to the compressor motor is opened for any reason, as for example, by opening a safety switch responsive to an abnormal load condition in the system, the circuit is completed again immediately upon the closing of the safety switch. In addition, rapid cycling of the thermal actuated control switch or conventional thermostat responsive to room temperature, will interrupt the operation of the compressor motor and then rapidly restart same.

Under such conditions, refrigerant pressure in the system may not have had sufficient time to equalize; therefore, when the circuit is closed, the split-phase motor will be unable to start the compressor. Typically, overload mechanisms are provided with the motor to interrupt the supply of current thereto, to prevent surge or locked rotor current from flowing to the motor for too long a period of time if the motor should fail to start.

The object of this invention is to provide a novel control circuit for air conditioning systems of the type discussed above, operable to prevent the compressor motor from being restarted for a predetermined period of time after operation thereof has been interrupted. The novel control is particularly suitable for use with split-phase motors of the type having a thermistor in series with the auxiliary or start winding.

SUMMARY OF THE INVENTION

This invention relates to an air conditioning system including a refrigeration unit having a motor driven compressor, a condenser, an evaporator and expansion means. The motor for driving the compressor is of the type known as a split-phase motor.

In series with the auxiliary or start winding of the split-phase motor is a positive temperature coefficient thermistor or other temperature responsive resistance element, having the characteristics that the resistance thereof will increase as a function of the temperature.

Upon startup of the compressor motor, the resistance of the series connected resistance element is low so substantially all of the starting current is supplied to the auxiliary and run windings. Once the motor has attained its predetermined speed, the resistance of the element will have risen to a level so that substantially all flow of current to the auxiliary winding is interrupted; only the run winding will remain in the circuit.

When operation of the refrigeration unit is stopped, the refrigerant pressure between the high and low sides of the system will be at a substantial differential. To prevent the restarting of the compressor motor for a predetermined period of time, so as to allow the pressure differential to substantially equalize, the control circuit regulating the operation of the compressor motor includes switch means responsive to the temperature of the resistance element connected in series with the start winding.

When the temperature of the resistance element has increased due to the flow of the current therethrough, the temperature responsive switch will open. However, during the normal operation of the compressor, the opening of such switch will have no effect thereon. Once the operation of the compressor motor has been interrupted, restarting of the compressor motor will be prevented so long as the switch remains open. The switch will close after a predetermined period of time has elapsed during which time the temperature of the thermistor and switch responsive thereto will return to a normal level.

The specific details of the invention and their mode or function will be made most manifest and particularly pointed out in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a type of air conditioning system including a refrigeration unit illustrating the present invention;

FIG. 2 is an enlarged detailed schematic wiring diagram of a portion of the air conditioning system illustrated in FIG. 1, showing a preferred form of control in accordance with my invention; and

FIG. 3 is a fragmentary schematic diagram of an alternative embodiment of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, and in particular to FIG. 1, there is schematically shown an air conditioning system employing a refrigeration unit incorporating a control in accordance with my invention. The refrigeration unit is representative of a type utilized in window mounted room air conditioners.

An outdoor heat exchange coil or condenser 10 is connected by means of line 11 with the discharge side of a suitable refrigerant compression mechanism, for example, a reciprocating type compressor 12. The gaseous refrigerant produced in compressor 12 flows to condenser 10 and is condensed by ambient air routed over the surface of the condenser by outdoor fan 13. Liquid refrigerant formed in condenser 10 flows via line 14, thermal expansion valve 15, and line 16 to evaporator 17. It is understood other suitable expansion devices such as a capillary tube, may be employed in place of expansion valve 15.

Liquid refrigerant in evaporator 17 is converted to vaporous refrigerant as it extracts heat from the medium, for example, air passed over its surface by fan 18. The cool air is discharged into the area being conditioned through a suitable outlet (not shown). Vaporous refrigerant from evaporator 17 flows via suction line 19 to compressor 12 to complete the refrigerant flow cycle.

Again referring to FIG. 1, a preferred form of the control circuit for the air conditioning system refrigeration unit hereinabove described is schematically shown. A suitable source of electric power, represented by lines L.sub.1 and L.sub.2, is connected to primary winding 24 of transformer 23. It is understood a poly-phase source of electric power may be employed if the circuit is suitably modified.

The secondary winding 25 of transformer 23 is connected to switch 26, responsive to the temperature of air circulating in the area being served by the equipment. When thermally actuated switch 26 is closed, current is supplied to control relay 27. Energization of control relay 27 closes normally open switches 29 and 30. Once switch 29 has been closed, fan motors 20 and 21 are energized thereby actuating fans 13 and 18. The closure of switch 30 supplies current through normally closed switches 31, 32 and 33 to compressor contactor coil 35. Device 34, to be more fully explained hereinafter, is connected in series with switches 31, 32 and 33 and coil 35. Energization of compressor contactor coil 35 closes normally open switch 36. The closure of normally open switch 36 connects motor 22 across lines L.sub.1 and L.sub.2, thereby starting compressor 12. The energization of compressor contactor coil 35 also closes normally open switch 37 for a reason to be more fully explained hereinafter.

Normally closed switches 31, 32 and 33 are safety devices; respectively a high-pressure cutout, a low-pressure cutout, and a motor overload cutout. Other safety devices known to the art, such as a low oil pressure cutout, may also be used. The occurrence of the condition protected against will open the particular switch, thereby either preventing the compressor motor from starting or stopping the compressor motor during the normal operation of the system.

Referring now to FIG. 2, there is shown an enlarged detailed view of a portion of the control circuit shown in FIG. 1, illustrating the details of my invention.

Motor 22 is of the type known to those skilled in the art as a split-phase motor. The split-phase motor includes parallel connected windings 40 and 41, respectively the main and auxiliary or start windings. Connected in series with auxiliary winding 41 is temperature sensitive resistance element 42, shown as a positive temperature coefficient thermistor. As is known to those skilled in the art, the positive temperature coefficient thermistor has a characteristic such that its resistance increases as a function of its temperature. In series with compressor contactor coil 35 is device 34. Device 34 includes normally closed switch 43, connected to bimetallic element 44. Bimetallic element 44 is responsive to the temperature of thermistor 42. As the temperature of thermistor 42 increases due to the flow of current therethrough, bimetallic element 44 warps to open switch 43, as represented by the solid lines of FIG. 2.

With switch 43 in its normally closed position, as represented by the dotted lines of FIG. 2, energization of coil 35 will occur upon the closure of switch 30. Switch 36 will close to provide current to the windings of motor 22. As noted hereinbefore, as the current flows to auxiliary winding 41 through thermistor 42, the current operates to increase the temperature and thus the resistance thereof. When the motor has attained its predetermined speed, winding 41 is effectively disabled by the substantial resistance presented to current flow thereto by thermistor 42.

The energization of contactor coil 35 closes normally open switch 37. Switch 37 provides a shunt or bypass about switch 43. Since switch 37 closes before switch 43 opens, the opening of switch 43 during normal running conditions of the compressor motor does not have any effect thereon.

When the operation of the compressor motor is interrupted, for example, by the opening of any one of the switches 31, 32 or 33, or by the opening of thermal responsive switch 26, the flow of current to coil 35 is interrupted, thereby opening switches 36 and 37.

When switch 36 opens, the flow of current to the compressor motor is interrupted. However, the increased temperature of the thermistor and of the bimetallic element 44 which is responsive thereto, has not been dissipated; switch 43 is still in its open position.

Assume the particular switch that has opened to interrupt the flow of current to compressor motor 22 subsequently recloses. With switch 43 still in its solid line position, in response to the temperature of bimetallic element 44, the flow of current to coil 35 is prevented.

If the compressor motor were to be permitted to restart immediately after it has been deenergized, the refrigerant pressure in the system would be at a substantially high differential. The compressor motor, since it is a split-phase type, would not have sufficient torque to restart the compressor. The locked rotor current caused to flow to the windings would deteriorate and in serious cases, completely burn them out.

By maintaining switch 43 in an open position for a substantially predetermined period of time, as determined by the time required for thermistor 42 and thus bimetallic element 44 to dissipate their heat to the ambient air, the pressure differential of the refrigeration unit will substantially equalize. Thus, when switch 43 is returned to its dotted line, or closed position, the pressure differential will be substantially equalized, and compressor motor 22 will have sufficient torque to start the compressor motor without introducing the problems hereinabove described.

Referring now to FIG. 3, an alternative embodiment of my invention is disclosed. In lieu of device 34, a second temperature responsive resistance element, such as a positive temperature coefficient thermistor 45 is placed in series with coil 35. Similar to device 34, thermistor 45 is responsive to the temperature of thermistor 42.

Upon the initial starting of compressor motor 22, the resistance of thermistor 45 is at a low level, so electrical energy is supplied therethrough to energize coil 35, to thereby close switches 36 and 37. As the temperature of thermistor 42 increases due to the flow of current therethrough, a concurrent increase occurs in the resistance of thermistor 45. The increased resistance of thermistor 45 is caused by the flow of current therethrough and the increased temperature of thermistor 42.

Although the passage of electrical energy through thermistor 45 is substantially interrupted, compressor motor 22 continues to operate due to the prior closure of switch 37. In all other respects, the operation of the embodiment shown in FIG. 3, is the same as heretofore described for the embodiment shown in FIG. 2.

A further benefit is obtained by employing a control circuit in accordance with my invention. As noted before, switch 29 will close upon the energization of relay 27 in response to the closure of switch 26. When switch 29 closes, fans 13 and 18 will be actuated. By actuating the fans, even if the compressor cannot be immediately restarted, due to switch 43 being in an open position, the flow of air over the condenser and evaporator caused thereby, will reduce the time required for the pressure differential to substantially equalize. This will insure the availability of sufficient torque to restart compressor motor 22 once switch 43 has closed due to the cooling of thermistor 42.

In addition, by maintaining the compressor deenergized for the substantially predetermined period of time so as to allow the temperature and resistance of the thermistor to return to its normal level, current flow to the start winding upon reenergization will be insured.

While I have described and illustrated a preferred embodiment of my invention, my invention should not be limited thereto but may be otherwise embodied within the scope of the following claims.

Claims

I claim:

1. In an air conditioning system operable to supply treated air to an area including a refrigeration unit comprising a compressor, a condenser, an evaporator and expansion means connected in a closed circuit, a motor for actuating said compressor, said motor having a run winding and a start winding connected in parallel, the improvement which comprises a control circuit to regulate the operation of said refrigeration unit comprising:

A. a supply circuit for providing electrical energy to said compressor motor, including thermally responsive means operable to energize said supply circuit in response to temperature conditions in said area;

B. a temperature responsive resistance element connected in series with said start winding of said compressor motor, the resistance of said responsive means substantially increasing as a function of its own temperature, the temperature thereof being increased by the flow of starting current therethrough; and

C. heat sensitive means responsive to the temperature of said resistance element, an increase in the temperature of said resistance element placing said heat sensitive means in a state such that flow of electrical energy therethrough is substantially interrupted, said means when in said state serving to prevent restarting of said compressor motor when the supply of electrical energy thereto has been discontinued, restarting of said compressor motor being prevented until the temperature of said resistance element has decreased to its normal level, said heat sensitive means being thereby placed in a state such that electrical energy is passed therethrough.

2. The combination in accordance with claim 1 wherein said heat sensitive means includes a bimetallic element; and a switch means operably connected thereto.

3. The combination in accordance with claim 2 wherein said control circuit further includes bypass means about said switch means to render said switch means inoperable during the operation of said compressor motor, said bypass means becoming inoperable when the supply of electrical energy to said compressor motor has been interrupted.

4. The combination in accordance with claim 3 further including:

A. means operable to supply a medium in heat transfer relation with said condenser; and

B. means operable in response to said thermally responsive switch to actuate said medium supply means, irrespective of the energization of said compressor motor.

5. The combination in accordance with claim 1 further including:

A. means operable to supply a medium in heat transfer relation with said condenser; and

B. means operable in response to said thermally responsive switch to actuate said medium supply means, irrespective of the energization of said compressor motor.

6. The combination in accordance with claim 1 wherein said heat sensitive means includes a second temperature responsive resistance element.

7. The combination in accordance with claim 6 wherein said control circuit further includes bypass means about said second resistance element to render said element inoperable during the operation of said compressor motor, said bypass means becoming inoperable when the supply of electrical energy to said compressor motor has been interrupted.

8. The combination in accordance with claim 7 further including:

A. means operable to supply a medium in heat transfer relation with said condenser; and

B. means operable in response to said thermally responsive switch to actuate said medium supply means, irrespective of the energization of said compressor motor.

9. The method of operating an air conditioning system including a refrigeration unit, having a compressor, a condenser, an evaporator and expansion means connected in a closed circuit, a motor for actuating the compressor including an auxiliary winding connected in parallel with a main winding, a temperature responsive resistance element being connected in series with the auxiliary winding, comprising the steps of:

A. supplying electrical energy through a device to energize the auxiliary and main windings of the motor to start the motor to actuate the compressor;

B. increasing the temperature and the resistance of the resistance element in series with the auxiliary winding to discontinue the operation of the auxiliary winding;

C. sensing the increased temperature of the resistance element upon the passage of electrical energy therethrough to place the device in a state whereby the flow of electrical energy therethrough is substantially interrupted in response to the increased temperature of the resistance element;

D. interrupting the passage of electrical energy to the main winding to deenergize the compressor motor; and

E. maintaining the device in its state whereby the flow of electrical energy is interrupted until the temperature of the resistance element has decreased to its normal level, reenergization of the compressor being prevented until the device is placed in a state whereby the flow of electrical energy therethrough may recommence, the reenergization of the compressor being thus prevented for substantially a predetermined period of time.

10. The method in accordance with claim 9 further including:

supplying a medium in heat transfer relation with said condenser, the supplying of said medium being independent of the operation of said compressor motor.