US3648214A

US3648214A - Condition-responsive electric switch mechanism

Info

Publication number: US3648214A
Application number: US83926A
Authority: US
Inventors: John L Slonneger
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-10-26
Filing date: 1970-10-26
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07

Abstract

A condition-responsive snap action electric switch mechanism, for use with a room air conditioner for instance, includes an operator which moves between extreme positions in response to a bellows. The bellows pressure increases and decreases in response to changes in temperature of the air passing over the evaporator. The switch also includes a first set of contacts to control energization of the compressor and a second set of contacts, including a snap-acting arm, to control energization of the evaporator and condenser fan motor. The operator includes an operating arm having a first portion which opens and closes the first set of contacts as the operator moves through a first, snap action, increment of travel between its extreme positions. The operating arm also includes a second portion which effects snap action of the snap-acting arm to open and close the second set of contacts as the operator moves through a second increment of travel separate from the first increment of movement.

Description

Slonneger Mar. 7, 1972 CONDITION-RESPONSIVE ELECTRIC SWITCH MECHANISM John L. Slonneger, Morrison, 111.

General Electric Company Oct. 26, 1970 Appl. No.: 83,926

Related U.S. Application Data 1969, abandoned.

Continuation-in-part of Ser. No. 819,635, Apr. 28,

References Cited UNITED STATES PATENTS Atchison....

Canter Weber et a1.

Primary Examiner-Bemard A. Gilheany Assistant Examiner--Dewitt M. Morgan Attorney-John M. Stoudt, Radford M. Reams and Ralph E. Krisher, Jr.

[57] ABSTRACT A condition-responsive snap action electric switch mechanism, for use with a room air conditioner for instance, includes an operator which moves between extreme positions in response to a bellows. The bellows pressure increases and decreases in response to changes in temperature of the air passing over the evaporator. The switch also includes a first set of contacts to control energization of the compressor and a second set of contacts, including a snap-acting arm, to control energization of the evaporator and condenser fan motor. The operator includes an operating arm having a first portion which opens and closes the first set of contacts as the operator moves through a first, snap action, increment of travel between its extreme positions. The operating am also includes a second portion which effects snap action of the snapacting arm to open and close the second set of contacts as the operator moves through a second increment of travel separate from the first increment of movement.

9 Claims, 15 Drawing Figures PATENTED 7 2 SHEET 2 0F 3 INVENTOR. John L. S Ion/wager, BY {WM At tor/7:5

PATENTEDMAR 7 I972 SHEET 3 []F 3 FIG/5 MOVEMENT FIGJZ FIG. 15

F'IGJO INVENTOR. John L,. Slog/7 A t: Carney.

CONDITION-RESPONSIVE ELECTRIC swrrcn MECHANISM CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-impart of my copending application Ser. No. 819,635 filedApr. 28, I969 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to condition-responsive electric switch mechanisms and, more particularly, to such mechanisms for use with refrigeration systems.

Refrigeration systems such as, for instance, room air condi' tions are customarily controlled by a switch which cycles the compressor on and off in response to the temperature of the air passing from heat exchange relationship with the evaporator into the room. Thus the temperature of the enclosure or room is maintained at about a predetermined level. Often at night the outside temperature falls sufficiently that the compressor may remain off for a long period. It still is desirable to run the evaporator and condenser fans to continue to bring in fresh air or circulate the air in the room. At times, such as the early morning hours, the ambient temperature falls sufficient that even circulation of uncooled air is uncomfortable. Thus a temperature-responsive switch is used to control the evaporator fan. Often in the past entirely separate switch mechanisms have been used for compressor and fan control. This requires great care in calibration to assure that the fan always runs when the compressor is energized. Prior art switch mechanisms using a single temperature-responsive element to control both the compressor and the evaporator fan have been so designed that sticking or erosion of the contacts will cause undesirable changes in the sequencing of the switching of the compressor and fan motors.

Also, in some cases it is desirable to have a multispeed fan which is cycled between various speeds of operation, with the compressor running continuously, to provide maximum cooling. This further complicates the control problem as it is desirable always to start the compressor in conjunction with a lowfan speed, and it is desirable that fanoperation without compressor operation be at low fan speed.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a new and improved condition-responsive switch mechanism.

It is another object of this invention to provide such an improved switch mechanism, particularly for use with a room air conditioner system, to control both the compressor and the motor for the evaporator and condenser fans.

A further object of this invention is to provide an improved temperature-responsive switch mechanism, to control the operation of the compressor and fan motor of an associated room air condition system, which is simple in design, rugged in construction and sure in operation.

A still further object of this invention is to provide an improved condition-responsive switch having at least two sets of contacts, in which operation of the various sets of contacts is always in the proper sequence.

The invention, in one embodiment thereof, provides a condition-responsive switch comprising a first set of contacts including a first stationary contact element and a first movable contact element mounted on a movable arm for movement between contact open and closed positions. The switch also has a second set of contacts including a second stationary contact element and a second movable contact element mounted on a snap-acting arm for snap action movement between contact open and closed positions. A contact operator is mounted for pivotal movement for selective engagement with the movable arm and the snap-acting arm to effect opening and closing of the first and second sets of contacts as the operator moves in opposite directions between first and second positions. The operator includes a toggle means for producing a snap action increment of movement of the operator intermediate its first and second positions. Condition-responsive means is connected to the operator for effecting movement of the operator between its first and second positions in response to predetermined sensed temperatures. The operator effects opening and closing of the first set of contacts during its snap action increment of movement and effects snap action movement of the snap-acting arm to open and close the second set of contacts during an increment of movement of the operator separate from its snap action increment of movement.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent, and the invention itself will be better understood by reference to the following description, taken in conjunction with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of an improved conditionresponsive switch mechanism embodying one form of the present invention;

FIG. 2 is an end view of the insulation base section of the switch mechanism, with some parts removed and some parts broken away for purposes of illustration;

FIG. 3 is a side elevational view of the switch mechanism of FIG. 1, partially in section and partially broken away, illustrating certain operational parts of the mechanism;

FIG. 4 is a somewhat schematic, partial side elevational view similar to FIG. 3, showing one position of certain operational parts of a switch mechanism incorporating another embodinient of the invention;

FIG. 5 is a view similar to FIG. 4, but showing the parts in another position;

FIG. 6 is a diagrammatic view of a refrigeration system with which the switch mechanism of the present invention is useful;

FIG. 7 is a schematic diagram of part of an electrical control system for the refrigeration system of FIG. 6, utilizing the switch mechanism of FIGS. 1-3;

FIG. 8 is a schematic diagram similar to FIG. 7 but utilizing the switch mechanism of FIGS. 4 and 5;

FIG. 9 is an end view, similar to FIG. 2, of the insulation base section of a switch mechanism incorporating yet another embodiment of the invention;

FIG. 10 is a partial perspective view of the contact operator of the switch mechanism shown in FIG. 9;

FIG. 11 is a somewhat enlarged schematic elevational view illustrating one position of certain operational parts of the switch mechanism of FIG. 9;

FIG. '12 is a view similar to FIG. 11, but showing the parts in another position;

FIG. 13 is a view similar to FIG. 11, but showing the parts in yet another position;

FIG. 14' is a view similar to FIG. 11, but showing the parts in still another position; and

FIG. 15 illustrates force-movement operating characteristics of the switch mechanism seen in FIG. 9 and is typical of such mechanisms which incorporate that form of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a condition or temperature-responsive electric switch mechanism 1 which embodies one form of the present invention, and often is also referred to as a room air conditioner control. The exemplification switch 1 is an improvement in the general type of temperature-responsive switch disclosed in U.S. Pat. Nos. 3,065,323, issued to Charles Grimshaw on Nov. 20, 1962; 3,065,320, issued to Richard W. Cobean on Nov. 20, 1962; and 3,096,419,- issued to Louis .I. Howell on July 2, 1963; all of which are assigned to General Electric Company, assignee of the present invention. Various aspects of such switch mechanism are shown in detail therein.

The switch 1 includes an insulating base or housing 2 which, for example, may be formed of molded phenolic thermosetting plastic, and a U-shaped frame 3, which is formed from a suitable material such as stainless steel and is securely mounted to the base 2 by some suitable means such as posts 4, which extend outwardly from each side of the base and are securely received in mating openings 5 in the frame 3. The frame 3 supports a bellows assembly 6 and a cover assembly 7, which includes means for mounting the switch upon a suitable supporting panel.

As best seen in FIGS. 2 and 3, the base 2 forms a housing for mounting the various sets of contacts of the switch mechanism and their associated terminals. For instance, base 2 serves as a mounting for terminals 8a and 8b, the inner portions of which are contained in a generally U-shaped internal cavity 9 of the base. The terminals 8a and 8b are securely fastened to the base so as to provide stable external connections for associated wiring and a stable support for a first set of contacts generally indicated at 10. A set 10 of contacts includes a stationary contact 11, having a contact element 12 electrically and mechanically connected to the terminal 8a by means of a stiff support arm 13; and a movable contact 14, having a contact element 15 electrically and mechanically connected to the terminal 8b by a movable or spring arm 16. The spring arm 16 biases the contact element 15 toward contact element 12 so that the contacts 11 and 14 are biased to a closed position.

The base or housing 2 also supports a second pair of terminals 17 and 18. A second set of contacts generally indicated at 19 is mounted in the chamber 9 and includes a first or stationary contact 20 having a contact element 21 electrically and mechanically connected to terminal 17 by a relatively stiff, return bent arm 22. The set 19 also includes a second or movable contact 23 having a contact element 24 electrically and mechanically connected to the terminal 18 by snap-acting or spring arm 25, including a toggle element 26. The spring arm 25 biases contact element 24 toward contact element 21 so that the

contacts

20 and 23 are biased to a closed position.

As best seen in FIG. 3, a screw 27 is threadily received in the base 2 and bears against the return bent arm 22 so as to assure proper positioning of the contact 20. As best seen in FIG. 2, a screw 18 is threadily received in the base 2 to selectively and adjustably bear against the toggle element 26 and a screw 29 is threadily received in the base 2 so as to selectively and adjustably bear against the movable contact element 24 when the

contact elements

21 and 24 are separated. It will be noted that the sets 10 and 19 of contacts are received in the cavity 9 in spaced-apart relationship and that the

spring arms

16 and 25 are substantially spaced apart and generally parallel.

The base 2, frame 3, bellows assembly 6 and cover 7 are securely joined together to form the outer covering of the switch mechanism 1 for mounting and protecting the various operative elements such as the sets of contacts 10 and 19. To this end the posts 4 are received in the mating openings 5; the frame 3 is formed with tabs 30 which are bent over the cover 7, and springs clips 31 are positioned engaging the cover 7 and bellows assembly 6. Other details of one manner of assembling these components may be had by reference to the aforementioned U.S. Pat. No. 3,065,323 Grimshaw and will not be described in further detail here as those features of the exemplification switch mechanism form no part of the present invention.

Referring now particularly to FIG. 3, to actuate the sets of contacts there is provided a contact operator 35 which includes a base portion 36 with a contact operating arm 37 secured thereto by some suitable means such as rivet 38 so as to extend into the cavity 9. The left end of base portion 36 (as seen in FIG. 3) is supported by one end of a snap action toggle spring or toggle element 39. The other end of the toggle spring is supported by a movable pivot member 40 which is supported by means of a pair of channels 41. The channels 41 support the movable pivot member 40 for longitudinal sliding movement within the base 2 and is moved by a differential-adjusting screw 42. This provides a linearly movable, adjustable support for the left side of the toggle spring 39. The screw 42 is threadily received in the base 2 and bears against the side of the pivot member 40 remote from the toggle spring 39 so that by adjusting the position of the screw 42 the tension of the toggle spring 39 may be adjusted.

The operator 35 is also supported by means of a pair of shoulders 43 which extend outwardly from each side of the base portion 36 and are received in cooperating slots 44 formed in the U-shaped frame 3. Thus the operator 35 is mounted for pivotal movement about the engagement of the shoulders 43 with the slots 44, with the toggle spring 39 continuously biasing the operator for movement in one direction, that is in a clockwise direction as seen in FIG. 3.

Spaced slightly forward from the shoulders 43, the base portion 36 is provided with a pair of laterally disposed knife edges 45 which provide arcuate pivots for supporting a bearing 46. The bearing 46 includes upper shoulders 47 which fit upon the knife edges 45 and depending, parallel pairs of struts 48. At their other ends, the struts 48 support a cup-shape base 49. The knife edges 45, being positioned to the left of the pivot points of the shoulders 43, may be used for providing a force on the operator 35 tending to rotate the operator in a counterclockwise direction (as seen in FIG. 3). To this end a range spring 50 engages, at its lower end, a nut 51 in which is threaded an adjusting screw 52. The lower portion of the screw 52 is provided with a shoulder portion 53 which engages the base 49 of the bearing 46. Also the lower end 54 of the screw extends through the base 49 and is received in a cup 55 of bellows 56. Thus the range spring 50, acting through the nut 51 and screw 52, exerts a continuing force on the bearing 46 tending to rotate the operator 35 in the counterclockwise direction. This force may be overcome by increasing the force which the bellows 56 exerts on the lower end 54 of the screw 52, which tends to lift the screw 52 and bearing 51 against the force of range spring 50.

The'increase and decrease of the force of the bellows 56 is utilized to provide a response to a condition external to the switch mechanism such as a sensed temperature. To this end the bellows is connected to a bulb 57 by means of a capillary tube 58. The bellows, bulb and capillary tube contain a charge of suitable vapor such as, for instance, dichlorodifluoromethane, butane or methyl chloride. Thus, as the temperature of the bulb rises or falls, the pressure of the vapor charge increases or decreases. This causes a corresponding increase or decrease in the force exerted on screw end 54 by the bellows 56, all in the well-known manner. Thus the pivotal movement of the operator 35 is responsive to the condition external to the switch and, in the cold control of the exemplification, it is responsive to a temperature sensed by the bulb 57.

By varying the compression of range spring 50 the sensed temperature level at which the cold control operates may be adjusted. To this end there is provided a manual adjustable cam 59 which is rotatably supported on cover 7 by a shaft 60 with a spring washer 61 captured between the cover 7 and a flange 62 formed on the shaft to retain the shaft and cam in a preset angular position. The cam 59 engages one end 63 of a cam follower 64 which is pivotally mounted on the U-shaped frame 3. The upper edge of the range spring 50 engages the underside of the cam follower 64 so that, as the cam follower responds to the rotary positioning of the cam, the amount of the compression of the range spring 50 between the cam follower and the nut 51 is changed. Also an opening 61a may be provided in cover 7 and a similar opening, not shown, in cam follower 64 for insertion of a screwdriver to calibrate the mechanism by adjusting the screw 52.

As thus far described, the toggle spring 39 exerts a continuing force on the operator 35 tending to cause it to rotate in a clockwise direction, and this force may be overcome by the range spring 50 to move the operator 35 in a counterclockwise direction. The force of the range spring'50 is opposed by the bellows 56 and is eflectively exerted on the operator 35 only when the temperature sensed by the bulb 57 is below a predetermined level so that the force bellows S6 is reduced below a predetermined level.

Assuming, for purposes of explanation, that the mechanism is in the position shown in FIGS. 2 and 3 and the bulb 57 senses an increasing temperature, the pressure of the vapor charge will increase. This causes an increase in the force exerted on the lower screw end 54 by bellows 56. This counters the force of range spring 50 and reduces the effective counterclockwise force exerted on operator 35. Eventually, at a predetermined sensed temperature, this counterclockwise force will be reduced sufficiently that toggle spring 39 will begin to pivot the operator 35 in a clockwise direction. As is well-known, the more the toggle spring moves the operator in this direction the stronger becomes the effective force exerted by the toggle spring. Thus the operator is snapped in its clockwise direction. Similarly, as the bulb senses a falling temperature the vapor pressure. and thus the bellows force is reduced, and the effective counterclockwise force exerted on the operator 35 by range spring 50 increases. Eventually, at a predetermined sensed temperature, the range spring will begin to move the operator in a counterclockwise direction against the toggle spring 39. As is well known, the more the operator moves in this direction the weaker becomes the effective force exerted by the toggle spring. Thus the operator is snapped back to the position shown in FIGS. 2 and 3.

The particular temperature at which the bellows will allow the range spring 50 to overcome the toggle spring 39 is determined by the setting of the cam 59. The differential-adjusting screw 42 is used to set the differential of the mechanism; that is the difference between the sensed temperature at which the operator will snap in one direction and the sensed temperature at which it will snap in the other direction.

The operating arm 37 is formed to cooperate with the contact sets and 19 to effect opening and closing of the contacts in a predetermined manner as the operator pivots in its two directions. To this end the operating arm 37 extends into the chamber 9 and includes a first portion or tang 65 which overlies the free end of spring arm 16. The operating arm 37 also includes a second portion or tang 66 which overlies the spring arm 25. The portions 65 and 66 are spaced apart a distance which is coordinated with the spacing of the

spring arms

16 and 25 to provide a proper sequence of operation of the sets of contacts 10 and 19.

More specifically, when the sensed temperature is at or above a predetermined level, so that the operator 35 has been pivoted to its extreme clockwise position, both the portions 65 and 66 are out of engagement with the cooperating spring arms and both sets of contacts are closed. As the sensed temperature decreases, the force of bellows 57 will decrease and the range spring 50, acting through the nut 51 and screw 52 will exert an increasing counterclockwise force on the operator 35. At a predetermined sensed temperature the effective counterclockwise force exerted on the operator 35 will be sufficient to overcome the toggle spring 39, and the operator will snap in a counterclockwise direction. This brings the tang 65 into engagement with spring arm 16 and opens the

contact elements

12 and 15. This counterclockwise snap action is suft'rcient to bring tang 66 into engagement with spring arm 25.

If the sensed temperature then begins to rise, the force exerted by the range spring 50 will be counteracted by an increasing force of the bellows 56 and at a second, slightly higher sensed temperature, the operator 35 will snap in a clockwise direction releasing the spring arm 16 so that the contact elements 12 and are again closed. Thus the

contact elements

12 and 15 are opened and closed as the operator 35 moves through a first increment intermediate its extreme clockwise and counterclockwise positions.

Assuming that after the

contact elements

12 and 15 are opened the sensed temperature continues to decrease, the vapor pressure decreases and the force of bellows 56 decreases. This causes an increasing efiective counterclockwise force to be exerted upon the operator 35 and thus the spring arm 25. This force continues to increase until it is sufficient to overcome the toggle spring element 26, and the spring arm snaps downward. This opens the

contact elements

21 and 24, with the contact element 24 coming to rest against the adjustable screw 29.

Thereafter, when the sensed temperature rises, the effective counterclockwise force exerted on the operator 35 decreases and, at a first predetermined temperature, slightly above that at which the

contact elements

21 and 24 separated, the spring arm 25 will snap upwardly to close the

contact elements

21 and 24. A further predetermined increase in the sensed temperature will cause the

contact elements

12 and 15 of contact set 10 to be snapped closed in the manner described above.

The adjustable screw 28, bearing against the toggle element 26 sets the sensed temperature at which the spring arm 25 will snap to its contact open position while the adjustable screw 29 engaging the contact element 24 in its contact open position determines the temperature differential of the contact set 19; that is the differential in the temperature at which the

contact elements

21 and 24 open and the temperature at which they close.

The spacing between the

spring arms

16 and 25 and the spacing between the operating arm portions or tangs 65 and 66 are coordinated so that the increment of travel during whichthe operating arm effects opening and closing of contact set 10 and the increment of'its travel during which it effects opening and closing of the contact set 19 are separated sufficiently that the contacts 11 and 14 may be cycled, that is repeatedly opened and closed, without effecting thepositioning of the

contacts

20 and 23 and the

contacts

20 and 23 cycled without effecting the positioning of contacts 11 and 14. Also the

contacts

20 and 23 will be opened only when the contacts l1 and 14 are open and, in those instances when both sets of contacts have been opened, the contacts 20 and23 will always close before the contacts 11 and 14.

A switch mechanism embodying the present invention, such as that described above, is of substantial advantage as a cold control for controlling the operation of a refrigeration system such as, for instance, an air conditioner. For purposes of illustrating its use in such an environment there is shown in FIG. 6, in s'implified schematic form, an air conditioning system 70 for controlling the temperature in a room or other enclosure 71. The system includes an evaporator or indoor coil 72, a compressor 73, an outdoor coil or condenser 74 and a restricter 75, all connected together by suitable tubing to form a circulating system for a suitable refrigerant. The air conditioning system also includes an evaporator fan 76 driven by a suitable electric motor 77 so that the fan 76 causes air to pass in heat exchange relationship to the evaporator and then to be dischargedinto the room or enclosure 71. This air may be air which is recirculated within the room or may be air drawn in from outside the enclosure. Normally the motor 77 also will power a condenser fan for directing air across the condenser 74.

FIG. 7 is an electrical schematic circuit diagram of a portion of a circuit for energizing the air conditioning system 70. The circuit includes a pair of

conductors

78 and 79 for connection to a suitable source of electrical power, such as the normal household supply. The compressor 73 is connected between the

conductors

78 and 79 in series with the contacts 11 and 14 of the'set of contacts 10. The evaporator fan motor 77 is connected between the

conductors

78 and 79 in series with the

contacts

20 and 23 of the set of contacts 19. The bulb 57 will be positioned to sense the temperature of the air being discharged from the evaporator 72 into the room or enclosure 71 so that, by suitable rotation of the shaft 60 the switch mechanism 1 may be set to maintain a desired temperature within the room.

As described above the operating arm 37 causes the contacts 11 and 14 to be cycled between their opened and closed position as the operator 35 moves through a first increment between its extreme positions under the control of the condition-responsive mechanism. This cycling will energize and deenergize the compressor 73 so that the air being discharged from the evaporator will have a temperature which oscillates closely about the temperature set by the shaft 60. It will be noted that, during this operation, the fan motor 77 is continuously energized. In the event that the air discharged from the evaporator continues to fall, despite the fact that the compressor 73 is deenergized, the temperature sensed by the bulb 57 will reach the point at which the operating arm 37 causes the

contacts

20 and 23 to be opened to deenergize the fan motor 77 and discontinue the flow of air. With air conditioning units this will tend to occur, for instance, in early morning hours when the outside temperature falls below the desired operating temperature of the air conditioning system. Continued operation of the fan 76 under such conditions, even without operation of the compressor 73, could cause an uncomfortable condition within the room.

Thus the switch mechanism 1, under normal ambient conditions calling for refrigeration, will cycle the compressor 73 so as to maintain the proper temperature within the enclosure, without cycling the fan and, when the ambient conditions become such that refrigeration is no longer required, the entire system, including both the compressor and the fan, will be deenergized to prevent unpleasant conditions within the enclosure.

It is often desired in refrigeration systems, particularly room air conditioners, to provide a multispeed evaporator fan which normally operates at a low speed but which is continuously energized at a high speed or is cycled between a low and high speed to provide maximum cooling when necessary. FIGS. 4 and illustrate, in a somewhat schematic form, another embodiment of the present invention for providing such multispeed control. The embodiment of FIGS. 4 and 5 differs from that of FIGS. 1 through 3 in the configuration of the operating arm and the number and positioning of the sets of contacts. Therefore, in describing FIGS. 4 and 5, the same reference numerals have been applied to those parts which remain basically the same. The mechanism is the same in FIGS. 4 and 5, differing only in that it shows the switch in two of its positions.

Referring now to FIGS. 4 and 5, there is provided a first set of contacts 80 having a pair of stationary contacts 81 and 82 and a movable contact 83. The contact 81 includes a contact element 84 which is electrically and mechanically connected to a suitable terminal (not shown) SHOWN) by a stiff arm 85.

The contact 82 includes a contact element 86 mounted on a stiff conducting arm 87. The contact 83 includes a doublesided contact element 88 which is connected to a suitable terminal (not shown) by a spring arm or snap-acting arm 89, including a toggle element 90. A second set of contacts 91 is provided and includes a stationary contact 92, having a contact element 93 electrically and mechanically connected to a suitable terminal (not shown) by a stiff conducting arm 94; and a movable contact 95 having a contact element 96, electrically and mechanically connected to a suitable terminal (not shown) by a spring arm 97. There is a third set of contacts 98 which includes a stationary contact 99, having a contact element 100 mounted on and electrically connected to a stiff arm 87, and a movable contact 101, having a contact element 102 which is electrically and mechanically connected to a suitable terminal by a spring arm 103.

The operator 35a includes the base portion 36 and a somewhat modified contact operating arm 37a. The operating arm 370 includes a first portion or tang 104 which overlies the spring arm 97 and a second portion in tang 105 which overlies both the spring arm 89 and the spring arm 103.

Referring now to FIG. 8 there is illustrated an electrically schematic diagram similar to FIG. 7 showing suitable connections for an air conditioning system utilizing the switch mechanism of FIGS. 4 and 5 in which the evaporator fan 76 is driven from a multispeed motor 77a. One branch circuit extends from conductor 78 to conductor 79 through the contacts 92 and 95 of contact set 91 for energizing the compressor. The circuit for the evaporator fan motor 77a includes two branches. One of these extends through the contacts 81 and 83 of contact set 80 and then directly to the terminal of the motor 77a for providing high-speed operation of the motor.

The other branch circuit extends through the

contacts

82 and 83 of the contact set and the contacts 99 and 101 of the contact set 98, and then to the terminal of motor 770 for providing low-speed operation. Thus the contact set 91 controls energization of the compressor 23, the contact set 80 controls the speed of operation of the fan motor 77a and the contact set 98 is effective selectively to energize the motor 77a, but only when the contact set 80 is positioned for lowspeed operation.

The spacing of the tangs or operating arm portions 104 and 105 are coordinated with the spacing of the

spring arms

97, 89 and 103 to provide the desired operation of the air conditioning system. For purposes of briefly describing this motor operation assume that the compressor is energized and the fan is connected for energization for high-speed operation to provide maximum cooling. For this condition the operator 35 is in its extreme clockwise position, not shown, so that the contacts 92 and 95 are closed, the contacts 81 and 83 are closed and the contacts 99 and 101 are closed. Asthe enclosure begins to cool and the temperature sensed by the bulb 57 drops, the operator 35a will pivot in a counterclockwise direction. This causes the tang 105 to relax the force exerted on spring arm 89, and the toggle element snaps the arm 89 downwardly. This disconnects the contacts 81 and 83 ahd connects the

contacts

82 and 83, as shown in FIGS. 5 and 8. This shifts the connection for the fan motor 77a to its low-speed terminal, as contact set 98 is closed, and the fan will begin operation at lower speed. If at this time the temperature of the air discharged from the evaporator into the enclosure rises, the operator 35a will be pivoted in its other or clockwise direction and move the contact 83 out of engagement with the contact 82 and back into engagement with the contact 81, to again provide high-speed operation of the fan. Thus, the fan will provide maximum cooling until a temperature within the enclosure is reached at which the desired temperature may be maintained by cycling of the compressor, coupled to a lowspeed fan operation.

When this occurs the temperature of the air discharged from the evaporator will continue to drop after the fan has been shifted to a low-speed operation and an increasing counterclockwise force will be exhibited on the operator 35. This counterclockwise force will increase until it overcomes the force of toggle spring 39 and snaps open the set of contacts 91, as shown in FIG. 4. This deenergizes the'compressor 23. Subsequently, normally the temperature of the air exhausted from the evaporator into the enclosure will tend to rise and the set of contacts 91 will reclose, as shown in FIG. 5, to reenergize the compressor. Normally this mode of operation continues, with the cycling of the compressor providing the necessary cooling to maintain the desired temperature as set by the shaft 60.

If, at some time as in early morning hours, the ambient temperature falls sufficiently, the temperature of the air exhausted from the evaporator will continue to fall, even though the compressor is deenergized. The operator 35a will remain in the position shown in FIG. 4 until the temperature drops a lower predetermined temperature. A continued decrease in the air temperature beyond this point will cause the contact set 98 to be opened to also deenergize the fan and prevent unpleasant conditions within the enclosure.

A subsequent rise in the temperature of air in the enclosure will cause the bellows 56 to counteract the force of range spring 50 and rotate the operator 35a in a clockwise direction so as to close the contact set 98 and reenergize the fan for a low-speed operation. A continued rise in the temperature in the enclosure will cause the operator 35 to snap from the position of FIG. 4 to that of FIG. 5 to reclose contacts 92 and 95 to start the compressor. A continued rise in the temperature of the air exhausted from the evaporator into the enclosure will cause the clockwise force on operator 35a to continue to increase and eventually move contact 83 from contact 82 to contact 81 for shifting the fan from low-speed to high-speed operation.

The positioning of the

spring arms

97, 89, and 103 is coordinated with the shape of the operating arm 37a, particularly the spacing between the tangs 104 and 105, such that the increment of movement of the operator 35a for cycling the fan motor 77a between .high and low speed, the increment of movement of the operator 35a for cycling the compressor 23 between its on and off conditions and the increment of movement of the operator 35a for cycling the fan motor 770 between off condition and a low-speed operational condition are separated sufficiently that thedesired sequence of operation is always provided. For instance this coordination is such that the speed of the fan motor is always shifted tolow-speed operation prior to the compressor being deenergized, and the compressor is always reenergized prior to the fan motor being shifted to high-speed operation. Also the fan motor is always shifted to low-speed operation prior to being completely deenergized, and when energized without energization of the compressor it is always energized for its low speed of operation.

- If desired contact element 102 could be provided with a backside for cooperation with a stationary contact, not shown, to provide a still lower speed of fan operation, rather an off.

Referring now to FIGS. 9-14, there is illustrated various features of yet another embodiment of the present invention. With particular reference to FIG. 9 there is shown a base 110, which is very similar to base 2, previously described, except that it is shaped to form a housing for mounting three sets of contacts and their associated terminals. For instance, base 110 serves as a mounting for terminals 111 and 1 12, the inner portions of which are contained in a generally U-shaped internal cavity 113 of the base. The terminals 111 and 112 are securely fastened to the base so as to provide stable external connections for associated wiring and a stable support for a first set of contacts or switch means generally indicated at 114. The set of contacts 114 includes a stationary contact 115, having a contact element 116 electrically and mechanically connected to terminal 111 by means of a stiff support arm 117; and movable contact 118, having a contact element 119 mechanically and electrically connected to terminal 112 by a spring arm 120. The spring arm 120 biases the contact element 119 toward the contact element 116 so that the

contacts

115 and 118 are biased to the contact closed position.

Base or housing 110 also supports

additional terminals

121, 122, 123 and 124. A stationary contact, in the form of a screw shaft 125 having a contact head or element 126 on one end is threadily received in terminal 121 to electrically and mechanically connect the contact 125 to the terminal 121. An additional stationary contact 127 is threadily received in a stiff arm 128 which electrically and mechanically connects it to terminal 122. The contact 127 includes a pair of contact heads or

elements

129 and 130 which are disposed on opposite sides of the arm 128. A second movable contact 131 is provided and includes a double-headed contact element 132 which is disposed between the

contact elements

126 and 129. Contact element 132 is mounted on a snap-acting or spring arm 133 which electrically and mechanically connects the contact element 132 to terminal 123. The snap-acting arm 133 includes a toggle element 134 which causes the arm 133 to move with a snap action and biases the arm 133 to a position in which contact element 132 engages contact element 129. Thus, contact

elements

126, 129 and 132 form a set of contacts with the movable contact being biased for engagement with one of the stationary contacts and movable to engagement with the other stationary contact.

A third movable contact 135 is provided and includes a contact element 136 electrically and mechanically connected to terminal 124 by a snap-acting or spring arm 137. The arm 137 includes a toggle element 138 which causes the arm 137 to move with a snap action and biases arm 137 to a position in which contact element 136 engages contact element 130.

A screw 139 is threadily received in the base 110 so as to selectively and adj ustably bear against movement contact element 136 when the

contact elements

130 and 136 are separated. A screw 140 is threadily received in the base 110 to selectively and adjustably bear against the toggle element 134. A third screw 141 is threadily received in the base 110 and selectively and adjustably bears against the toggle element 138. In this regard it will be understood that the snap-acting or

spring arms

133 and 137, with their associated

toggle elements

134 and 138, are received in the cavity 113 in spaced-apart relationship and that the

arms

133 and 137 are generally parallel. As is known in the art, the setting of screw 140 will determine the operating point or temperature of snap-acting arm 133 while the spacing between

contact elements

126 and 129 will determine the temperature differential of snap-acting arm 133. Similarly, the setting of screw 14] will determine the operating temperature of snap-acting arm 137 while the spacing between contact element l30 and the end of screw 139 will determine the temperature differential of snap-acting arm 137.

In order to actuate the sets of contacts there is provided a contact operator 145 which may be essentially the same. as contact operator 35, previously described, except for a modified contact operating arm 146 which extends generally at right angles to the base portion 36. The operating arm 146 includes a first portion or tab 147 and a second portion or tab 148, which are spaced apart along the long axis of the operating arm 146 and thus are spaced apart in the direction of movement of the operating arm. The portion 147 includes a lower edge 149 which is disposed to engage spring arm while portion 148 includes an upper edge 150, disposed to engage snap-acting arm 133, and a button or lower edge 151, disposed to engage the snap-acting arm 137. In this regard the

springarms

120, 133 and 137 are spaced apart in the cavity 113 generally in the direction of movement of the operating arm 146. It will be understood that the contact operator is designed to engage with and to be operated by a bellows assembly, a range spring and a snap-acting spring means in the form of a toggle spring which may be identical with the bellows 56, range spring 50 and toggle element or spring 39 shown in FIGS. 3-5, for instance. In fact such operating components and their arrangement may be the same as previously described for other embodiments of this invention and therefore will not be described or shown in detail with regard to this particular embodiment.

As discussed generally with regard to the other embodiments, such an arrangement of parts means that the operator 1.45, as it moves from one of its extreme positions to the other, will have a first creep increment of movement, then a snap action increment of movement and finally a second creep increment of movement. The

arms

120, 133 and 137 are so arranged with respect to each other and with respect to the contact operating am 146 that the operating arm causes each of the snap-acting

arms

133 and 137 to be actuated with a snap action during a corresponding one of the increments of creep movement of the contact actuator 145 while the spring arm 120 is engaged by the edge 149 to effect opening and closing of the set of contacts 114 during the snap action increment of movement of the operator 145.

, Assuming for purposes of illustration that the switch mechanism of FIG. 9 is connected in an air conditioning control generally as indicated in FIG. 8 for the embodiment of FIGS. 4 and 5 and referring particularly to FIGS. "-14, there now will be described a sequence of operation for the switch mechanism of FIG. 9. HO. 11 illustrates the condition when the operator 145 is moved to its extreme position corresponding to the bellows 56 and bulb 57 sensing a predetermined low temperature, that is the compressor and the fan are both off. Assuming the sensed temperature begins to rise, the pressure of the vapor charge in the bulb and bellows will increase. This increases the force exerted by the bellows in opposition to the range spring and reduces the effective force of the range spring. As explained with regard to the embodiment of FIGS. 1-3, the toggle spring 39 beings to cause the operator to move upwardly (as seen in FIG. 11) with a creeping motion. As the contact operator 145 creeps upwardly the button or edge 151,

which has been holding spring arm 137, gradually decreases the force it is exerting on arm 137 to a level where the arm 137 snaps upwardly because of the toggle element 138 so as to move contact element 136 into engagement with contact element 130. When contact element 136 engages contact element'130, the fan motor is energized on low speed.

Thereafter, if the bulb 57 continues to sense a rising temperature the operator 145 will continue upwardly with a creep movement. If, however, for some reason such as drawing in cool outside air the bulb senses a decreasing temperature the operator will reverse itself and creep downwardly. This will cause the button 151 to increase the force on the arm 137 until, at a calibrated force value corresponding to a predetermined sensed temperature it will effect a downward or counterclockwise snap action of the spring arm 137 to disengage the contact element 136 from contact element 131 and bring it into engagement with screw 139.

Assuming the bulb senses a rising temperature the operator will continue to creep upwardly (as seen in FIGS. 11-14) until the forces acting on the operator 145 pass through a balance condition and the toggle spring 39 assumes control. The toggle spring then moves the operator 145 upwardly through a second or snap action increment of movement. This snap action increment of movement carries the operator from the position shown in FIG. 12, where button 151 is just engaging snap-acting arm 137, to the position shown in FIG. 13 where the edge 149 has released the arm 120, so that it has closed

contact elements

116 and 119 with a snap action, and edge 150 has just come into engagement with snap-action arm 133 but snap-acting arm 133 is still in its downwardly biased position with contact element 132 engaging contact element 129. Closing of

contact elements

116 and 119 causes the compressor motor to be energized to begin a refrigerating or air conditioning operation.

Thereafter, if the temperature falls the vapor pressure in the bellows and bulb will fall and the forces acting on the contact operator 145 will just over balance so that the contact operator 145 is snapped through its snap acting increment of movement in the other direction by the toggle spring 39.

However, assuming the temperature sensed by the bulb 57 continues to rise the vapor pressure will continue to increase and the contact operator 145 will continue to move upwardly through its second creep increment of movement so that the edge 150 exerts an increasing force on the snap-acting arm 133 and, at an upper predetermined temperature the arm 133 will snap in a clockwise direction (as seen in FIGS. ll-14) so that contact element 132 is moved from engagement with contact element 129 to engagement with contact element 126. This shifts the fan motor from low speed to high speed. Thereafter the mechanism will shortly reach mechanical stop and the compressor will run and the fan motor will run at high speed so long as the temperatures above this higher predetermined temperature are sensed.

As the temperature sensed by the bulb 57 falls the reverse occurs. That is, briefly stated, the contact operator 145 first moves through a creep increment of movement from the position shown in FIG. 14 to the position shown in FIG. 13, during which the force exerted by the edge 150 on snap-acting arm 133 is reduced to a calibrated value at which arm 133 snaps in a counterclockwise direction, moving contact element 132 from contact element 126 to contact element 129. This cuts the fan motor from high to low speed. Thereafter the contact operator 145 is moved through its snap action increment of movement from the position shown in FIG 13 to the position shown in FIG. 12. During this increment of movement the edge 149 engages spring arm 120 and opens

contact elements

116 and 119 with a snap action. This deenergizes the compressor motor. Thereafter, the contact operator moves through a second increment of creep movement during which the button or lower edge 151 of arm 146 increases the force on snap acting arm 137 to effect a counterclockwise snap action of that arm for moving contact element 136 out of engagement with contact element 130. This completely deenergizes the evaporator and condenser fan motor so as to, in effect,

completely turn off the associated air conditioning unit.

Referring now particularly to FIG. 15 there is shown an illustration of the force-movement operating characteristics of I the mechanism of FIGS. 9-14. This diagram is similar to-that shown and described in applicant's prior US. Pat. No. 3,354,280 issued on Nov. 2l, 1967 and assigned to General Electric Company, assignee of the present invention. Line 155 illustrates the force-movement characteristic corresponding to the bulb sensing an increasing temperature. The mechanism starts at position A, which corresponds generally to the switch positions shown in FIG. 11. The operator moves through its first creep increment of movement which corresponds to curve A, B, C, B, D with the portionB, C indicating the snap action movement of snap-acting arm 137. Point D illustrates the condition at which the forces on the operator 145 become balanced and the operator then snaps through its snap acting increment of movement indicated by curve D, E, F, G, G with portion E, F indicating the closing of

contact elements

116 and 119. Point G indicates the position at which the forces acting on the contact operator l45 again become balanced and, assuming an increasing temperature, the operator then moves through its second increment of creep movement indicated by curve portion G, H, I, J with portion H, I indicating the snap action movement of snap-acting arm 133.

Now assuming a condition in which the switch is shown in the configuration generally indicated in FIG. 14 and assuming the bulb 57 to sense a falling temperature, curve J, L, M, N illustrates the first creep increment of movement of the contact operator 145 with L, M showing the snap-acting movement of snap action arm 133 from the position in FIG. 14 to the position of FIG. 13. Position N indicates another balanced force condition on the operator 145 so that thereafter it snaps through its snap action increment of movement, illustrated by curve N, O, P, R, R, with O, R indicating the opening of

contact elements

116 and 119. At R the forces on the contact operator again become balanced, and assuming a continuing decreasing temperature the operator will move through its second increment of creep movement, as illustrated by curve R, S, T, A with portion S, T illustrating the snap action of snap-acting arm 137 from the position of FIG. 12 to the position of FIG. 11.

While in accordance with the Patent Statutes, I have described what, at present, are considered to be preferred embodiments of my invention, it will be obvious to those skilled in the art that numerous changes and modifications may be made therein without departing from the invention, and it it therefore aimed in the appended claims to cover all equivalent variations as fall within the true spirit and scope of the invention.

What I claim as new and desire to be secured by Letters Patent of the United States is:

1. A condition-responsive switch, comprising:

a. a first set of contacts including a first stationary contact element and a first movable contact element mounted on a movable arm for movement between contact open and closed positions;

b. asecond set of contacts including a second stationary contact element and a second movable contact element mounted on a snap-acting arm for snap action movement between contact open and closed positions;

c. a contact operator mounted for pivotal movement for selective engagement with said movable arm and said snap-acting arm to effect opening and closing of said first and second sets of contacts as said operator moves in opposite directions between first and second positions;

d. said operator including snap-acting spring means for producing a snap action increment of movement of said operator intermediate its first and second positions;

e. condition-responsive means connected to said operator for effecting movement of said operator between its first and second positions in response to predetermined sensed temperatures;

f. said operator effecting opening and closing of said first set of contacts with snap action during the snap action increment of movement of said operator;

g. said operator effecting snap action movement of said snap-acting arm to open and close said second set of contacts with snap action during an increment of movement of said operator separate from the snap action increment of movement of said operator.

2. A switch as set forth in claim 1, wherein:

a. said movable arm is biased to one of its positions and is movable to the other of its positions;

b. said snap-acting arm is biased to one of its positions and is movable to the other of its positions;

4 c. said operator includes a first portion overlying said movable arm for moving said movable arm to its one position and releasing said movable arm for return to its other position as said operator moves in opposite directions through its snap action increment of movement; and

d. said operator includes a second portion overlying said snap-acting arm for exerting a force on said snap-acting arm to effect snap action movement of said snap-acting arm to its one position and reducing the force on said snap-acting arm to effect snap action movement of said snap-acting arm to its other position as said operator moves in opposite directions through an increment of movement separate from its snap action increment of movement.

3. A switch as set forth in claim 2, wherein: said snap-acting arm includes a toggle element biasing said snap-acting arm to one of its positions and a first manually adjustable stop means engages said toggle element for selectively adjusting the temperature sensed by said condition responsive means corresponding to the increment of movement of said operator separate from its snap action increment of movement during which said snap-acting arm moves between its switch open and closed positions.

4. A switch as set forth in claim 3, wherein: said snap-acting arm, including said toggle element, provides a differential in temperature sensed by saidcondition-responsive means at which said second set of contacts is opened and at which said second set of contacts is closed; said switch further including second manually adjustable stop means for engaging said snap-acting arm to limit opening movement of said snap-acting arm and thereby selectively adjust the temperature differential.

5. A condition-responsive switch mechanism comprising:

a. first switch means having first and second switch positions;

b. second, snap-acting, switch means having first and second switch positions;

c. third, snap-acting, switch means having first and second switch positions;

d. contact operating means movable between first and second positions in actuating relation with said first, second and third switch means for effecting operation of said first, second and third switch means;

e. condition-responsive means connected to said contact operating means for effecting movement of said contact operating means between its first and second positions in response to predetermined temperatures;

f. said contact operating means including snap-acting spring means so that movement of said contact operating means between its first and second positions includes a first creep increment, a snap action increment and a second creep increment;

g. said contact operating means being arranged with respect to said first, second and third switch means so as to effect snap action operation of said first switch means during said snap action increment of movement of said contact contact operating means. 6. A switch mechanism as set forth in claim 5 wherein at least one of said snap acting switch means includes a toggle element biasing it to one of its switch'positions and said mechanism further includes adjustable stop means engaging said toggle means for selectively adjusting the temperature sensed by said condition-responsive means corresponding to the operation of said at least one of said snap acting switch means.

7. A condition-responsive switch mechanism, comprising:

a. a first stationary contact, a first movable contact mounted on a movable arm, said movable arm being biased to a contact closed position and movable to a contact open position; 1

b. second and third spaced-apart, stationary contacts, a second movable contact mounted on a first snap-acting arm, said first snap-acting arm being biased to a position with said second movable contact engaging said second stationary contact and movable to a position with said second movable contact engaging said third stationary contact;

c. a fourth stationary contact, a third movable contact mounted on a second snap acting arm, said second snapacting arm being biased a contact closed position and movable to a contact open position;

d. contact operating means movable between first and second positions;

g. said contact operating means including a contact operating arm mounted in interfering relationship with said movable arm for effecting snap action movement of said movable arm between its contact open and closed positions during the snap action increment of movement of said contact operating means; i

h. said contact operating arm also being in interfering relationship with said first and second snap-acting arms for effecting snap action movement of said first snap-acting arm between positions with said second movable contact in engagement with said second and third stationary contacts and for effecting snap action movement of said third snap-acting arm between its open and closed positions as said contact operating means moves through its first and second increments of creep movement respectively.

8. A switch mechanism as set forth in claim 7, wherein said first and second snap-acting arms are spaced apart generally along the direction of movement of said operating arm and said operating arm includes a portion interposed therebetween for engaging said first snap-acting arm during said first creep increment of movement and for engaging said second snap-acting arm during said second creep increment of movement.

9. A switch mechanism as set forth in claim 7, wherein at least one of said snap-acting arms has a toggle element biasing it to one of its positions and said mechanism further includes adjustable stop means for selectively adjusting the temperature sensed by said condition-responsive means corresponding to the operation of said at least one of said snap-acting arms.

Claims

1. A condition-responsive switch, comprising: a. a first set of contacts including a first stationary contact element and a first movable contact element mounted on a movable arm for movement between contact open and closed positions; b. a second set of contacts including a second stationary contact element and a second movable contact element mounted on a snap-acting arm for snap action movement between contact open and closed positions; c. a contact operator mounted for pivotal movement for selective engagement with said movable arm and said snap-acting arm to effect opening and closing of said first and second sets of contacts as said operator moves in opposite directions between first and second positions; d. said operator including snap-acting spring means for producinG a snap action increment of movement of said operator intermediate its first and second positions; e. condition-responsive means connected to said operator for effecting movement of said operator between its first and second positions in response to predetermined sensed temperatures; f. said operator effecting opening and closing of said first set of contacts with snap action during the snap action increment of movement of said operator; g. said operator effecting snap action movement of said snapacting arm to open and close said second set of contacts with snap action during an increment of movement of said operator separate from the snap action increment of movement of said operator.

2. A switch as set forth in claim 1, wherein: a. said movable arm is biased to one of its positions and is movable to the other of its positions; b. said snap-acting arm is biased to one of its positions and is movable to the other of its positions; c. said operator includes a first portion overlying said movable arm for moving said movable arm to its one position and releasing said movable arm for return to its other position as said operator moves in opposite directions through its snap action increment of movement; and d. said operator includes a second portion overlying said snap-acting arm for exerting a force on said snap-acting arm to effect snap action movement of said snap-acting arm to its one position and reducing the force on said snap-acting arm to effect snap action movement of said snap-acting arm to its other position as said operator moves in opposite directions through an increment of movement separate from its snap action increment of movement.

4. A switch as set forth in claim 3, wherein: said snap-acting arm, including said toggle element, provides a differential in temperature sensed by said condition-responsive means at which said second set of contacts is opened and at which said second set of contacts is closed; said switch further including second manually adjustable stop means for engaging said snap-acting arm to limit opening movement of said snap-acting arm and thereby selectively adjust the temperature differential.

5. A condition-responsive switch mechanism comprising: a. first switch means having first and second switch positions; b. second, snap-acting, switch means having first and second switch positions; c. third, snap-acting, switch means having first and second switch positions; d. contact operating means movable between first and second positions in actuating relation with said first, second and third switch means for effecting operation of said first, second and third switch means; e. condition-responsive means connected to said contact operating means for effecting movement of said contact operating means between its first and second positions in response to predetermined temperatures; f. said contact operating means including snap-acting spring means so that movement of said contact operating means between its first and second positions includes a first creep increment, a snap action increment and a second creep increment; g. said contact operating means being arranged with respect to said first, second and third switch means so as to effect snap action operation of said first switch means during said snap action increment of movement of said contact operating means and to effect snap action operation of said second switch means and said third switch means during respective creep Increments of movement of said contact operating means.

6. A switch mechanism as set forth in claim 5 wherein at least one of said snap acting switch means includes a toggle element biasing it to one of its switch positions and said mechanism further includes adjustable stop means engaging said toggle means for selectively adjusting the temperature sensed by said condition-responsive means corresponding to the operation of said at least one of said snap acting switch means.

7. A condition-responsive switch mechanism, comprising: a. a first stationary contact, a first movable contact mounted on a movable arm, said movable arm being biased to a contact closed position and movable to a contact open position; b. second and third spaced-apart, stationary contacts, a second movable contact mounted on a first snap-acting arm, said first snap-acting arm being biased to a position with said second movable contact engaging said second stationary contact and movable to a position with said second movable contact engaging said third stationary contact; c. a fourth stationary contact, a third movable contact mounted on a second snap acting arm, said second snap-acting arm being biased a contact closed position and movable to a contact open position; d. contact operating means movable between first and second positions; e. condition-responsive means connected to said contact operating means for effecting movement of said contact operating means between its first and second positions in response to predetermined temperatures; f. said contact operating means including snap-acting spring means so that movement of said contact operating means between its first and second positions includes a first creep increment, a snap action increment and a second creep increment; g. said contact operating means including a contact operating arm mounted in interfering relationship with said movable arm for effecting snap action movement of said movable arm between its contact open and closed positions during the snap action increment of movement of said contact operating means; h. said contact operating arm also being in interfering relationship with said first and second snap-acting arms for effecting snap action movement of said first snap-acting arm between positions with said second movable contact in engagement with said second and third stationary contacts and for effecting snap action movement of said third snap-acting arm between its open and closed positions as said contact operating means moves through its first and second increments of creep movement respectively.