Room Air Conditioner Having Compressor With Variable Capacity And Control Therefor

Abstract

A room air conditioner with a compressor having variable capacity is provided by the invention, with the variable capacity automatically adjusted to balance with the refrigeration load of the space being cooled. A movable valve progressively opens a portion of the compressor cylinder to the suction side of the system so that a progressively reduced volume of active cylinder is available for compression. The volume available for compression is automatically proportioned by a control arrangement which is actuated by the temperature of the space being cooled.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of our copending U.S. patent application, Ser. No. 2838, filed Jan. 14, 1970 now abandoned.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a room air conditioner having a variable capacity compressor and controls therefor.

2. Description of the Prior Art

In order to operate a refrigerant system at a reduced load where the compressor utilized includes only a single cylinder, a method must be devised to provide the system of which the compressor is a part with a reduced load capacity. Some methods utilized to provide this reduced system capacity include hot gas bypass, a solid state speed control for the compressor, suction gas throttling or reheat. In each of these methods the amount of power consumed by the system to obtain partial capacity is not correspondingly reduced relative to the power consumed at full capacity. Obviously such an arrangement is wasteful, requiring the home owner or refrigeration system owner to pay for power which should not actually be required for part capacity operation. Compressors have, therefore, been designed which provide variable capacity, in and of themselves, so that the system power requirements at partial load are reduced.

Compressors which have only a single cylinder but yet have a variable capacity are well known in the compressor field. An example of a compressor having a reduced capacity arrangement that utilize valves to vary the active volume of the compression cylinder is shown in U.S. Pat. No. 1,481,358. In the arrangement shown therein, valves are opened to provide reduced capacity and are manually actuated so that a portion of the cylinder, may be opened to the suction side of the system. However, the structure shown in this patent does not disclose any arrangement or control system whereby control of the compressor capacity is obtained automatically through actual load conditions. In U.S. Pat. No. 877,492, an automatic arrangement is shown for controlling unloading valves which reduce the capacity of a compressor (pump) but the device of this patent is directed towards the regulation of the operation of a gas engine so that the automatic means controlling the valve arrangement is actuated by the actual speed of the engine. Thus, this patent in no way suggests the automatic operation of a single cylinder compressor utilized in an air conditioning or refrigeration system which is responsive to the actual loading imposed on it by the space for which it offers cooling.

Other U.S. Pat. Nos. relating to one aspect or another of compressor capacity control include: 2,036,846, 2,036,847, 2,170,846, 2,555,005 and 3,272,786, cited in our original application. However, none of these patents are directly concerned with room air conditioners of the single cylinder hermetic compressor type, and are not provided with structural arrangements, nor control arrangements, which yield modulating control (in the sense of progressive or incremental steps) of compressor capacity. That is, they appear to provide arrangements in which the reduction of compressor capacity available is of a predetermined, given amount.

SUMMARY OF THE INVENTION

In accordance with the principles of the invention, a room air conditioner has a single cylinder hermetic compressor of variable capacity attained by a series of ports spaced axially along the cylinder wall and adapted to be placed in communication with the suction side of the refrigeration system. These ports are capable of being progressively closed and opened by a valve member movable in a direction generally parallel to the cylinder axis. Movement of the valve member is governed by control pressures responsive to changes in the temperature of the room being cooled. The valve member covers all the ports in the cylinder wall at full compressor capacity. As the demand for cooling in the room is progressively reduced, the valve member is moved to uncover, in corresponding progressive fashion, portions or all of successive ports closer and closer to the head of the cylinder. This vents more and more of the cylinder volume to the suction side of the refrigeration system.

In one embodiment of the invention, the control pressure is provided by a generator containing oil or refrigerant which has a conduit leading to the valve member so as to provide a pressure on the driving piston of the valve member when the oil or refrigerant containing generator has been activated. Activation of the generator is provided by a thermostat conveniently located in the room being cooled. When the room temperature falls to a selected level, a pair of contacts close providing current flow to a heating coil surrounding the generator. As this generator heats, the oil or refrigerant provides an increasing pressure against the piston of the valve body, urging the piston in a direction to uncover the ports in the cylinder wall. Although such a thermostat actuated switch is an on-off device, the heating coil and generator can be sized so that intermittent current flow to the heating element of the generator will, as the time of current flow increases, move the piston more and more towards a port opening position. In the embodiment disclosed, substantially a 50 percent reduction can be obtained in capacity for the compressor in small increments.

In a second embodiment of the invention, the control pressure is provided by a tap off the condenser of the refrigeration system, this tap containing a three way solenoid which is again actuated by contacts activated by the thermostat so as to provide a pressure from the condenser to the piston in the valve body whenever the temperature in the room falls below that set on the thermostat. A conduit is also connected into the solenoid valve so that, with room temperatures above or equal to that set on the thermostat, provision is made for permitting the back flow of control pressure to the suction side of the system to thereby equalize the pressure on each side of the valve body.

In a third embodiment of the invention, condenser pressure is again utilized as the control pressure for the valve body but in this embodiment no flexible bellows is disposed between the piston and the conduit leading from the condenser. Thus, a certain amount of control pressure leakage is permitted to flow past the piston into the suction side of the system to provide pressure equalization when full capacity of the compressor is required. With this arrangement, a two-way solenoid valve is all that is required to provide and interrupt condenser control pressure from being imposed on the valve body piston. A significant savings over the cost of the second embodiment may be attained by the use of the two-way solenoid valve.

DRAWING DESCRIPTION

FIG. 1 is a view of the compressor cylinder of the instant invention in cross-section with the generating arrangement shown generally schematically;

FIG. 2 is a side view of the apertured plate of the valve body of the embodiment of the invention shown in FIG. 1;

FIG. 3 is a view similar to FIG. 1 but showing the second embodiment of the invention;

FIG. 4 is a view similar to FIGS. 1 and 3 but showing the third embodiment of the invention; and

FIG. 5 is a schematic view of a room air conditioner provided with a variable capacity compressor and control system according to the invention, and with the control system shown in removed relation to the air condition-er for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a compressor 8 (shown only fragmentarily) having a cylinder 10 can be seen. A piston 12 is disposed in the cylinder of the compressor for reciprocating movement so as to provide a pressurized refrigerant gas for a refrigeration or air conditioning system. Piston 12 is connected to a crank shaft 14 by a connecting rod 16 as is conventional in a compressor configuration so that rotation of crank shaft 14 actuates the piston 12 in its reciprocating motion.

A suction manifold 18 formed in a housing 9 of the compressor 8 is provided for introducing low pressure refrigerant gas into the cylinder 10 and a discharge manifold 20, also formed in the compressor housing, is provided for receiving the pressurized gas discharged from the cylinder 10. Each of these manifolds is partly formed in an end member 22 of the housing by casting or the like so as to provide an inexpensively manufactured configuration. Disposed inwardly of the end member 22, as shown in the drawings, is a valve plate 24 having both a discharge valve 26 and a suction valve 28, with the valve plate 24 disposed between the cylinder 10 and the end member 22 so as to complete the enclosure for the manifolds 18, 20. A pair of gaskets 30 and 32 are disposed on opposite sides of the valve plate 24 to insure that there is a gas tight seal between it and the end of the cylinder 10 and end member 22. It should be clear that, on the suction stroke of the piston 12, gasses are drawn from the suction manifold 18 through the suction valve 28 into the cylinder 10 and that, on the exhaust stroke of the piston 12, gasses are forced outwardly through the discharge valve 26 into the discharge manifold 20 and from there through a discharge port 34 disposed in end plate 22 so as to provide for the exit of compressed gasses to the condenser of the refrigeration system, the discharge valve 26 and suction valve 28 serving as check valves to prevent the backward flow of gasses into the cylinder 10 or discharge manifold 20, respectively. The valves 26 and 28, of course, are spring biased into a generally closed position by being formed as a resilient member or the like.

As is conventional, the piston 12 reciprocates within the cylinder 10 between a bottom dead-center position as illustrated in FIG. 1 to a top dead-center position closely adjacent to valve plate 24. During this movement of the piston 12 a volume within cylinder 10 is swept, this volume depending upon the diameter of the bore of the cylinder 10 and the length of the stroke of the piston 12, and such sweep represents the full capacity of the compressor.

In order to provide for reduced capacity of the compressor, means are provided to reduce the active volume of the sweep of the piston 12 during which actual compression of the refrigerant gas is maintained. A series of ports indicated 36 and 38 in FIG. 1 are disposed in a wall 40 forming the cylinder 10, there being two ports 36 in aligned relationship and three ports 38 in aligned relationship. Such alignment is substantially perpendicular to the axis along which the piston 12 reciprocates. The ports 36 and 38 open to and are in confluent relationship with corresponding ports 42 and 44 disposed in an apertured plate 46 mounted on the wall 40 of cylinder 12, a milled face 48 on cylinder 10 providing for this mounting. The apertured plate 46 can best be seen in FIG. 2 where it is easily ascertained that the ports 42 and 44 are in an aligned relationship similar to the ports 36 and 38 so that a flow of refrigerant gas may pass outwardly of the cylinder 10 when the ports are open to the suction side of the system. The ports 36 are spaced axially, relative to the direction of the cylinder axis, from the ports 38; and so are, correspondingly, the ports 42 spaced from ports 44. All of the ports are in that part of the length of the cylinder traversed by the head of the piston.

The aperture plate 46 forms one side wall of a control valve 50 which controls the degree to which the ports 42 and 44 are open so as to correspondingly control the degree to which refrigerant gas from the cylinder 10 escapes as the piston 12 sweeps from its bottom dead-center position to its top dead-center position.

Disposed within the control valve 50 is a slide member 52. The slide member 52 includes an enlarged portion 54 which, during the reciprocating motion of the slide member 52, has one side that covers or uncovers the ports 42 and 44, the slide member 52 being guided in its movement across the ports 42 and 44 by a thickened portion 56 of a second side wall 58 of the valve 50, disposed opposite to the apertured plate 46, by the elongated ends of the ports 42 and 44 and by an enlarged portion 59 on apertured plate 46. The control valve 50 is generally square in cross-section and its enclosure is completed by an end wall 60 disposed in abutting relationship with valve plate 24 and an end cap 61. A flange 62 is integral with end wall 60 to provide one convenient area for connection of the end wall 60 with the side wall 58.

Disposed substantially medially of the end wall 60 is a port 64. The port 64 passes completely through the end wall 60 and opens into confluent relationship with a port 66 disposed in valve plate 24, the said port 66 communicating with the suction manifold 18. Suction manifold 18 is thereby opened to the interior of control valve 50.

The end cap 61 includes a blind bore 68 which terminates short of the exterior of the end wall 61 so as to provide a capped portion 70 to substantially close this end of the control valve 50. A bore 72 of the same diameter as blind bore 68 is disposed in an intermediate body member 74 of control valve 50. This element is located between the end cap 61 and the thickened portion 56 of side wall 60 and the termination of apertured plate 46. The coaxial bores 68 and 72 mount within their confines a piston 76 that is capable of movement rectilinearly so as to move reciprocating slide member 52.

The piston 76 is urged in one direction of its movement by a flexible diaphragm or flexible bellows 78 made of a flexible plastic material. The flexible diaphragm 78 is positioned between capped portion 70 and intermediate body member 74 of control valve 50 to provide a gas tight seal therebetween and so that pressurization of it will tend to move it deformingly and, due to its abutment against the piston 76, move the piston 76 therewith. The piston 76 includes a cylindrical tab portion 80 which is insertingly held in a bore 82 extending through the end of the slider member 52 to aid in the conjoint movement of these members.

Slider member 52 also includes a larger bore 83 which extends axially for substantially the full length of the slidable member 52 from the end opposite to the end having bore 82 to form a substantially hollow cylindrical shape for the reception of an expansion spring means 84. Expansion spring 84 is in the form of a circular coiled compression spring and provides a resilient bias to the slide member 52 urging it into a position where it covers the ports 42 and 44 thereby placing the cylinder 10 in a full capacity supplying condition, with the bore 83 providing a guiding means for the spring 84 during its expansive and contractive movements. A cylindrical boss 86 is made integral with the end wall 60 so as to extend in axial alignment with the axis of the compression spring 84. Cylindrical boss 86 is of such a diameter that it fits within the coils of an expansion spring and thereby provides an additional alignment and guiding means for the spring 8 in its expanding and contracting movements.

The control valve 50 is completed by the use of a vent 88 connected to a stand pipe disposed to prevent oil from entering the control valve 50. The vent 88 is in communication with the suction side of the system in the hermetically sealed can enclosing the compressor.

Extending through the capped portion 70 of control valve 50 is a bore 90, this bore being of smaller diameter than the bore 68 but being in communication therewith so as to permit a pressure flow to the flexible diaphragm 78. A conduit 92 is connected with the bore 90 so as to be in fluid tight seal with it to convey a supplied control pressure to the control valve 50. The conduit 92 extends to a closed reservoir 94 which may contain either oil or a refrigerant so that the reservoir 94, the conduit 92 and a portion of the bore 68 form a closed system in order that an increase in pressure of the oil or refrigerant contained in reservoir 94 will be transmitted to the rolling diaphragm 78 to thereby impart rectilinear motion to the piston 76. To increase the pressure in reservoir 94 and send a pressure signal to the rolling diaphragm 78, a heating element 96 is extended in a coiled relationship around the outer periphery of the reservoir 94. Thus, the heat imparted through this heating coil to the reservoir 94 will cause a consequent pressure rise in the reservoir 94 and an increased pressure on the movable diaphragm 78. If the rolling diaphragm 78 is to be constructed of a somewhat pervious material (for economy) there is a possibility that the closed system formed by the reservoir 94, conduit 92 and bore 68 may have leakage inwardly or outwardly. To eliminate this possibility a sufficient quantity of mercury 95 or the like is placed in the end of the conduit 92 at the valve body, and within the bore 68 against the rolling diaphragm 78, so that the mercury will occupy the bore 68 regardless of the valve position and thus provide a barrier to the passage of fluids or gasses inwardly or outwardly through the rolling diaphragm 78. Alternatively, a relatively more expensive metallic, non-permeable diaphragm may be utilized and, in this case, no mercury is required.

In order to move the control valve 50 so as to proportion the capacity of the compressor directly to the refrigeration load, a control means is provided for the application of electrical energy to heating element 96. A control circuit 98 forms this means and provides a flow of electric current to the heating coil 96 by the use of a pair of on-off contacts 100 and 102 which form a switch 104. Contact 100 is electrically connected to a lead 106 which extends to and is connected to one end of the heating coil 96, with this contact mounted generally so as to be non-movable and rigid with the remainder of the system. The contact 102 is, in turn, connected to a load 108 that extends to a source of current such as the 110 volts provided for the space being cooled. Another lead 110 extends from this electrical supply and is connected to the opposite end of the heating coil 96. Movable contact 102 is mounted on a thermostat 112 within the cooled space so as to be movable with the coiled temperature sensing element 114 of the said thermostat. Thus, the contact 102 moves as the temperature in the area being cooled changes and, as the set temperature for the space is attained, contact 102 electrically contacts contact 100 providing a closed circuit for the flow of electricity into the heating coil 96.

The operation of the first embodiment of the invention will now be detailed. At full capacity of the compressor 8, the cylinder 10 has its entire volume swept by the piston 12, with the control valve 50 in a position so as to close off the ports 36 and 38. Thus, the compressor acts at its full capacity and, until a signal is received relative to the reaching of the previously selected temperature of the space being cooled, the compressor will continue to provide full capacity to the refrigeration system. When the temperature of the space being cooled reaches that set by the thermostat 112, the contacts 102 and 100 move into electrical connection providing heating to the reservoir 94 and imposing a pressure on rolling diaphragm 78. This pressure moves rolling diaphragm 78 against piston 76 urging this piston towards opening of the ports 42 and 44.

Since the heating coil does not provide an instantaneous buildup of heat in the reservoir 94, the initial pressure imposed on the piston 76 only compresses the spring 84 a slight amount and thereby only moves the sliding member 52 a slight amount to partially uncover the first row of ports 42. Only a small volume of gas under compression is thereby permitted to escape to the suction side of the system through ports 64 and 66 to the suction manifold 18 or through vent 88. Since the skirt of the compressor piston 12 in its compression stroke will cover the ports 36, the remaining volume of refrigerant gas contained in cylinder 10 is compressed and discharged through the discharge valve 26 to the discharge manifold 20. Thus, only a slight change in the capacity of the compressor has been arrived at which will accommodate slight changes in the refrigeration load in the space being cooled. In the event that this space temperature remains at that which the contacts 100 and 102 are in electrical conducting condition then the heating coil 96 will continue to heat the reservoir 94. This provides additional pressure and urges piston 76 and slidable member 52 in a further capacity reducing direction thereby opening port 42 further. As long as the contacts 100 and 102 stay closed, the heating element 96 will continue to heat the fluid contained in the reservoir 94 urging the slidable member 52 further towards a capacity reducing position until both the ports 42 and 44 are fully uncovered.

In the embodiment illustrated in FIG. 1, these ports are located at such a position that a maximum reduction to 50 percent of capacity of the compressor in nearly infinite steps may be achieved. It should be obvious, however, that additional capacity reduction could be arrived at by providing additional ports or by locating the ports 42 and 44 at a position which is closer to top dead-center of the piston 12.

It should be clear from the arrangement just described that capacity reduction of the compressor is directly responsive to the temperature reduction of the room being cooled and that this occurs in a modulating fashion rather than in on-off fashion. The volume of the refrigerant gasses actually compressed corresponds to the demand for cooling and results in lowered power requirements for the total system and reduced system cycling. Probably most important however is that modulating the capacity, as distinguished from on-off cycling, results in better humidity control of the room being conditioned.

The second embodiment of the invention can be seen in FIG. 3. In this embodiment as well as the embodiment shown in FIG. 4, similar reference numerals are utilized to indicate similar elements to those in the first embodiment. This embodiment is substantially similar in all respects to the first embodiment save for the method and means for providing a control pressure to the sliding member 52. More specifically, a conduit 92' extends from the bore 90 of control valve 50 to a solenoid valve 116 which functions as a three-way valve. Solenoid valve 116 includes an axially extending bore 118 that extends substantially for the full length of the solenoid valve. A series of radially spaced ribs or the like (not shown) may be utilized within the bore 118 to provide guidance for a solenoid actuated plunger member 120. This member is disposed so as to move longitudinally within the bore 118 to alternatively open or close ports 122 and 124 located within the bore 118, with a pair of valve portions 126 and 128 formed on the plunger member 120 and shaped generally conically and being adapted to close the ports 122 or 124, respectively.

The conduit 92' communicates with the bore 118 intermediate the ports 122 and 124 so as to be able to be supplied by pressure from either a conduit 130 or a conduit 132, with the conduit 130 connected to the higher, discharge side of the compressor 8 and the conduit 132 connected to the lower or suction side of the compressor 8 whereby the conduit 92', dependent upon the position of the plunger member 120, obtains a flow of high pressure refrigerant from the conduit 130 or a flow of low pressure refrigerant from the conduit 132. A biasing means 134 in the form of a coil compression spring is disposed within the bore 118 so as to locate the plunger member 120 in a position sealing against the port 122. Actuation of an electrically energized coil 136 of the solenoid valve 116 moves the plunger member 120 to a position where the port 122 is opened and the port 124 is closed so that the conduit 92' may have imposed thereon the high or discharge pressure of the compressor.

Actuation of the solenoid valve 116 is accomplished in a manner similar to actuation of the heating coils 96, the thermostat control switch 106 providing a flow of current through leads 106' and 110' to actuate the solenoid valve 116 into providing compressor discharge pressure (control pressure) into conduit 92'.

Operation of the second embodiment of the invention is substantially similar to the first embodiment. Control pressure is either provided by the conduit 130 (high) or conduit 132 (low). This pressure flows into conduit 92' through the solenoid valve 116 to the flexible diaphragm 78 which is actuated to move slidable member 52 in a capacity reducing direction of the compressor. Thus, the control pressure is either on or off so that the slidable member 52 moves from full capacity to one half capacity, the control means thereby providing load proportioning of full or one half load.

The embodiment illustrated in FIG. 4 also uses, as the actuating control pressure for the slidable member 52, the compressor discharge or condenser pressure of the refrigeration system. In this embodiment of the invention, however, only a two-way solenoid valve 116' is required to permit the flow of the discharge pressure into a conduit 92". A solenoid actuated plunger member 120' is again disposed in a bore 118 formed in the solenoid valve 116. This member includes a valve portion 126' formed with a general conical shape which opens or closes a port 122' which is in confluent relationship with the conduit 92" leading to the valve control body 50'. Control pressure is provided through the conduit 130 from the discharge pressure of the compressor, this pressure being present in the bore 118 of solenoid valve 116'. Upon actuation of the solenoid plunger 120', the solenoid actuated plunger member 120' moves away from the port 122' so that the conical portion 126' of the plunger permits the flow of discharge pressure into conduit 92". This imposes the conduit discharge pressure on the control valve 50' by this pressure being present in both bores 68' and 72'.

In this embodiment of the invention no flexible diaphragm 78 is present in the control valve 50' so that the discharge pressure of the compressor is imposed directly on the piston 76'. In view of the omission of the rolling bellows in this embodiment of the invention, a certain amount of the discharge pressure from the compressor may pass by the piston 76' so that bleeding of the discharge pressure into the suction side of the system may be obtained. By this means, as the solenoid valve 120' moves to its discharge pressure supplying position and then to its closed position, such discharge pressure is slowly bled through the bores 68' and 72' to relieve pressure from the piston 76' to provide substantially the same operation for this embodiment of the invention as described for the second embodiment.

In FIG. 5 there is illustrated an arrangement in which the variable capacity compressor is incorporated in a room air conditioner 138, and a control system with additional detail, in part, is shown schematically and in separated relation from the room air conditioner. Parts which are common to the parts shown in FIG. 1 are given identical numerals.

The air conditioner 138 is in large part conventional and includes a compressor and variable capacity valving arrangement of the type shown in FIG. 1 provided in a hermetically sealed shell 140. The room air conditioner also includes a condenser 142, evaporator 144, room air fan 146 and the usual connecting refrigerant lines which are not enumerated but which have directional arrows showing the flow of refrigerant. The generator 94 contains a two-phase charging fluid selected to correspond with the operating temperature limits of the control system. The resistance heater 96 is wrapped about the generator and the whole is encased within an insulating jacket 148. Both the first thermostat 112, and a second thermostat 150 may be of the same general character as illustrated in FIG. 1, that is of a bimetal type, but with a temperature control knob 152 being provided to permit the simultaneous adjustment of the two thermostats 112 and 150 upwardly or downwardly while maintaining a relatively constant temperature differential between the two thermostats as set. A third thermostat 154 may be provided in heat exchange relation with the generator 94 and serves essentially as an overheat safety device which breaks the circuit to the resistance heater 96 if a condition pervails in which the high pressure corresponding to a high temperature in the generator would possibly rupture the piston diaphragms or break down the charging fluid. A main on-off switch 156 is also shown.

The room air conditioner as illustrated in FIG. 5 is also provided with means for controlling the rate of air flow through the evaporator in accordance with compressor capacity. This is accomplished by providing a branch control line 158 connected to a control cylinder 160 which converts changes in the control pressure from the generator to mechanical force through linkage 162 to control the position of an air flow damper 164 illustrated as being in the return air inlet of the room air side of the air conditioner. The control cylinder 160 operates in the same general fashion as the control cylinder for the valve member varying the capacity of the compressor operates.

The manner in which the system operates is as follows. The control knob 152 is turned to adjust the thermostats 112 and 150 to set a desired room temperature, for example, the setting may be 75.degree. for the thermostat 112 and, assuming a 6.degree. differential between the thermostats 112 and 150, the thermostat 150 will accordingly be set at 69.degree.. With a room temperature in excess of the 75.degree., the compressor will operate at full capacity. As the temperature in the room is reduced, assuming a cooling load that the compressor at full capacity is more than capable of handling, the temperature of the room will drop. When it reaches 75.degree., the thermostat 112 closes and energizes the resistance heater 96. The temperature of the charging fluid will rise very slowly as a function of the heat applied and the heat loss through the insulation. This temperature increase will evaporate more charging fluid and increase the pressure in the control tubing 92 and 158. This increased pressure acts on the pistons in the two control cylinders causing them to push against the biasing springs and move to an equilibrium position. If this pressure is sufficient to cause some venting from the compressor cylinder, a reduced capacity of the compressor results. At the same time, the damper 164 is moved toward a slightly closed position to reduce the air flow through the evaporator. If the room temperature remains below the 75.degree. setting, a continued increase of control pressure will cause a further reduction in compressor capacity and a further decreased air flow from the blower. If with this situation prevailing the temperature of the room being air conditioned rises above the 75.degree. setting of the thermostat 112, the heater 96 will be deenergized by opening of the thermostatically controlled contacts in thermostat 112. Then the temperature of the charging fluid in the generator 94 will slowly decrease as a function of the ambient temperature and the heat loss through the insulation 148 of the generator jacket. As a result, the control actuators will move toward the full capacity of the compressor, and full air flow through the evaporator.

If the temperature in the room is below 75.degree., and the compressor is operating at fully reduced capacity and with the air flow through the evaporator at its reduced value, and the temperature in the room continues to decrease to 69.degree. because of the relatively small cooling load in the room, the thermostatic switching contacts in thermostat 150 will open and stop compressor operation. It is in this situation of course that the overheat safety switch 114 may be desirable since the heater 96 remains energized by the continued closure of the switch contacts in thermostat 112.

However, assuming that the charging fluid attains an equilibrium pressure and temperature, when the room temperature increases again above the setting of the thermostat 150, operation of the air conditioner will again commence, it being appreciated it will be with reduced capacity of the compressor and air flow so that in effect a relatively low level of cooling will be obtained. It is considered likely to be advantageous in this arrangement that the control pistons for the compressor and for the air flow remain in positions giving reduced capacity, particularly in connection with the compressor since the starting torque required should accordingly be reduced.

In an alternative arrangement of the thermostatic switches 112 and 150, the switch 112 would be connected to receive power from the line running from switch 150 to the compressor, rather than directly from the AC line as shown, so that when switch 150 opens the power to the heater 96 is also cut off.

The main intent of the reduced air flow through the evaporator with the reduced capacity of the compressor is to obtain the best dehumidification possible under the circumstances. With the reduced air flow, there is greater liklihood that a part of the cooling capacity will be available for the removal of latent heat, and not wholly expended on removal of sensible heat of the air passing through the evaporator.

It is noted that the temperature examples given are examples only and that the temperature differential noted may be selected according to the particular system.

Claims

We claim:

1. A room air conditioner for cooling and dehumidifying a room, comprising:

a single cylinder hermetic compressor, including a piston, and a cylinder wall having a number of ports therein spaced axially relative to the cylinder axis, in that part of the length of the cylinder wall traversed by the head end of said piston;

valve means for said ports, said valve means having one position corresponding to full capacity operation of said compressor closing all of said ports, and being movable in a direction generally parallel to said cylinder axis and generally transverse to the direction of any gas flow through said ports, to an opposite position in which all of said ports are open;

means placing said ports, when open, in communication with the suction side of the compressor;

control means for said air conditioner including means for effecting movement of said valve means in accordance with temperature changes in a selected range in the room conditioned by said air conditioner, said valve means moving progressively in a direction from said one position toward said opposite position in response to progressively lower temperatures in said range in said room, so that the compression stroke of said piston is, in effect, progressively shortened to provide progressively reduced capacity of said compressor while continuing to operate to provide reduced cooling and dehumidification of said conditioned room.

2. A room air conditioner according to claim 1 wherein:

said means for effecting movement of said valve means includes means providing the motive power for moving said valve means independent of changes in discharge and suction pressures of said compressor.

3. In a room air conditioner according to claim 1 wherein:

said control means includes first thermostatic means for selecting a first temperature established in the upper limit of said selected range, and second thermostatic means for selecting a second temperature establishing a lower limit of said selected range.

4. A room air conditioner according to claim 3 including:

means for adjusting said first and second thermostatic means together with a relatively constant temperature differential therebetween to effect a change of said selected temperature range as a whole.

5. A room air conditioner according to claim 4 wherein:

said first thermostatic means controls switch means for controlling said means effecting movement of said valve means; and

said second thermostatic means controls switch means for starting and stopping compressor operation.

6. A room air conditioner according to claim 1 wherein:

said air conditioner includes a refrigerant evaporator and blower means for effecting air flow through said evaporator to said room; and

means for reducing air flow through said evaporator in accordance with the reduction of the capacity of said compressor.

7. In a room air conditioner according to claim 6 wherein:

said means for effecting movement of said valve means associated with said compressor is connected to simultaneously operate said means for reducing air flow.