US3564865A

US3564865A - Automotive air-conditioning system

Info

Publication number: US3564865A
Application number: US848014A
Authority: US
Inventors: Gary E Spencer; Mervin R Butts
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1969-08-06
Filing date: 1969-08-06
Publication date: 1971-02-23
Anticipated expiration: 1988-02-23

Abstract

IN PREFERRED FORM, AN AUTOMOTIVE AIR-CONDITIONING SYSTEM HAVING A COMPRESSOR, A CONDENSER, AN EXPANSION VALVE, AN EVAPORATOR AND A FLOW REGULATING THROTTLING VALVE SERIALLY CONNECTED TOGETHER, RESPECTIVELY, AND INCLUDING AN EQUALIZER LINE BETWEEN THE EXPANSION VALVE AND THE THROTTLING VALVE OUTLET. THE EQUALIZER LINE IS NORMALLY BLOCKED BY A THERMALLY ACTUATED VALVE WHICH OPENS WHEN THE COMPRESSOR TEMPERATURE EXCEEDS A PREDETERMINED MAXIMUM. THE OPENING OF THE EQUALIZER LINE TRANSMITS COMPRESSOR INLET PRESSURE TO THE EXPANSION VALVE WHICH OPENS IT TO ALLOW REFRIGERANT TO FLOW THROUGH THE EVAPORATOR AND INTO THE COMPRESSOR FOR COOLING PURPOSES.

Description

Feb. 23, 1971 s. E. SPENCER ETAL' AUTOMOTIVE AIR-CONDITIONING SYS TEM 2 Sheets-Sheet 1 Filed Au 6, 1969 Gaz- BY 5 S Wm WWW 3 aw i u H T'TOHNE Y Feb. 23, 1971 E. SPENCER ETI'AL v 3,564,865

AUTOMOTIVE AIR-CONDITIONING SYSTEM Filed Aug. 6, 1969 v 2 SheetsSheet z I N VENTURS 5023/ a: J'pazzcer 6 BY 776ruz'z7 6 62:

(94am I ATTORNEY United States Patent 3,564,865 AUTOMOTIVE AIR-CONDITIONING SYSTEM Gary E. Spencer, Dayton, and Mervin R. Butts, West Milton, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Aug. 6, 1969, Ser. No. 848,014 Int. Cl. F25!) 41/00 US. Cl. 62-197 6 Claims ABSTRACT OF THE DISCLOSURE In preferred form, an automotive air-conditioning system having a compressor, a condenser, an expansion valve, an evaporator and a flow regulating throttling valve serially connected together, respectively, and including an equalizer line between the expansion valve and the throttling valve outlet. The equalizer line is normally blocked by a thermally actuated valve which opens when the compressor temperature exceeds a predetermined maximum. The opening of the equalizer line transmits compressor inlet pressure to the expansion valve which opens it to allow refrigerant to flow through the evaporator and into the compressor for cooling purposes.

This invention relates to an automotive air-conditioning system and more particularly to one having an equalizer line extending between an expansion valve and the outlet of flow regulating throttling valve.

In compression cycle air-conditioning systems, an expansion valve provides a variable fluid flow restriction though which high pressure liquid refrigerant from a condenser is expanded into a low pressure liquid state. The expansion valve is used to control the rate of refrigerant expansion so as to maintain a predetermined superheat temperature at the evaporator outlet. The term superheat relates to the temperature of refrigerant vapor flowing from the evaporator and is a measure of the heat load on the evaporator. For maximum efficiency only enough liquid refrigerant, which relates to refrigerating capacity, should be supplied to the evaporator by the expansion valve to overcome the heat load in the evaporator. A low superheat at the evaporator outlet indicates an excessive refrigerating capacity to overcome a given heat load in the evaporator which corresponds to inefficient operation. A high superheat at the evaporator outlet indicates an insufficient refrigerating capacity to overcome a given heat load in the evaporator which also corresponds to inefiicient operation.

The expansion valve is opened in response to the temperature of refrigerant in the evaporator outlet. More particularly, the temperature is sensed by a capillary tube or power element which contains a pressurizable fluid. The refrigerant temperature is transformed into fluid pressure within the power element. The fluid pressure is transmitted to one side of a diaphragm within the expansion valve by a tube. Movement of the diaphragm in response to the fluid pressure operates a valve element which controls the refrigerants rate of expansion through the expansion valve.

A throttling valve between the evaporator outlet and the compressor inlet controls the flow of refrigerant through the evaporator in response to evaporator pressure. By controlling the refrigerant flow, pressure in the evaporator is maintained above a predetermined minimum value which prevents the temperature of the evaporator from falling below freezing and consequently the formation of ice on the evaporator surface. This permits the evaporator to be operated at its greatest efficiency without ice formation which could block air flow through the evaporator.

'ice

Normally, the air-conditioning system operates at relatively high evaporator pressures under high load conditions. During these high load conditions, the throttling valve is open to promote maximum fluid flow through the evaporator and to provide maximum refrigerating capacity. When the evaporator is subjected to lighter heat loads, the system operates at proportionately lower evaporator pressures. However until the evaporator pressure falls below the predetermined minimum value, no throttling valve action will occur. When the evaporator pressure drops below the predetermined minimum, the valve closes. When the throttling valve is completely closed, the flow of refrigerant through the evaporator is severely reduced to the amount of refrigerant which leaks around the valve. With the throttling valve closed, a balanced pressure-temperature condition is established across the evaporator. To the expansion valve, this pressure-temperature balance across the evaporator represents a condition of low superheat. Consequentially, the expansion valve responds by closing to reduce refrigerant flow through the evaporator to zero.

The compressor which relies to some extent on refrigerant for cooling may undesirably tend to operate at higher than normal temperatures during a no-fiow condition. To prevent this high temperature operation of the compressor, an equalizer line is provided between the compressor inlet and the expansion valve. When the throttling valve is closed, the compressor inlet pressure sensed by the expansion valve through the equalizer line is considerably lower than the evaporator inlet pressure. This reduced pressure transmitted by the equalizer line causes the expansion valve to open and allow refrigerant to flow into the evaporator. consequentially, refrigerant leakage through the throttling valve cools the compressor.

During operation of the air-conditioning system with the throttling valve closed, considerable effort is expended to cool the compressor by refrigerant leakage through the throttling valve. The actual heat load on the evaporator may be quite low during this period of operation. As a consequence, relatively low efiiciency can be expected when the air-conditioning system is operating under such conditions. Because cooling of the compressor by leakage through the throttling valve is only required under extreme temperature conditions, it is desirable to block the equalizer line during normal operation of the system and to unblock the equalizer line only when the compressor needs cooling.

The present invention includes an equalizer line normally blocked by a thermally responsive valve. A heat sensing element in the vicinity of the compressor senses an abnormal temperature level and opens the thermally responsive valve in the equalizer line. As previously explained, this opening of the equalizer line causes refrigerant flow through the expansion valve, the evaporator and the throttling valve to cool the compressor.

An object of the invention is to provide a simple and effective control arrangement for an automotive air-conditioning system, which is activated in response to a predetermined maximum temperature of the compressor to supply refrigerant to the compressor for cooling purposes but which is normally inactive during normal operation of the air-conditioning system.

A further object of the inventor is to provide a simple and effective control arrangement for an automotive air-conditioning system including a normally closed valve in the equalizer line which is opened in response to a predetermined maximum compressor temperature to open an expansion valve which consequentially supplies refrigerant to the compressor for cooling purposes.

A still further object of the inventor is to improve the efliciency of an automotive air-conditioning system having an equalizer line between the compressor inlet and the expansion valve by placing a normally closed thermally actuated valve in the equalizer line which opens in response to compressor temperature above a predetermined maximum to effect cooling refrigerant flow through the expansion valve to the compressor.

Further objects and advantages of the invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIG. 1 is a schematic illustration of an air-conditioning system according to the present invention;

FIG. 2 is a schematic illustration like FIG. 1 of a second embodiment of the present invention;

FIG. 3 is a vertical sectioned view of the expansion valve shown in FIG. 1;

FIG. 4 is a vertical sectioned view of the throttling valve shown in FIG. 1;

FIG. 5 is a sectioned view of a thermally actuated valve for use in the air-conditioning system illustrated in FIG. 1; and

FIG. 6 is a sectioned view of a second thermally actuated valve which can be used in the air-conditioning system illustrated in FIG. 1.

In FIGS. 1 and 2 of the drawings, an automotive airconditioning system is illustrated including a compressor 10 which has magnetic clutch pulley assembly 12 on its shaft adapted to be rotated by an internal combustion engine (not shown). Refrigerant vapor is compressed by the compressor 10 and discharged through an outlet or discharge line 16 to a condenser 14. There the high pressure refrigerant vapor is condensed to a high pressure liquid state by transferring its heat of condensation to air flowing through the condenser. The high pressure liquid refrigerant and a small amount of high pressure vapor subsequently flows through a line 20 into a receiverdehydrator 18. The receiver-dehydrator 18 allows only liquid refrigerant to pass into a line 22 and retains vapor. The liquid refrigerant then fiows through the line 22 into an expansion valve 24. The refrigerant flow through expansion valve 24 is through an orifice passage which expands the refrigerant to a low pressure state. The low pressure liquid refrigerant subsequently flows from expansion valve 24 through an evaporator inlet line 26 into an evaporator 28. In the evaporator 28 the low pressure liquid refrigerant boils to a vapor state and draws its heat of vaporization from air passing through the evaporator. Duct work (not shown) directs air through. the evaporator where it is cooled and into the vehicle interior. The low pressure refrigerant vapor then passes from the evaporator 28-through an evaporator outlet line 30 and into a throttling valve 32. The throttling valve 32 controls the flow of refrigerant through the evaporator 28 to maintain a predetermined minimum pressure in the evaporator which prevents its temperature from falling below freezing. The low pressure refrigerant vapor next flows from throttling valve 32 through a compressor inlet or suction line 34 back into the compressor 10 where it is once again pressurized.

The expansion valve 24 is more particularly shown in FIG. 3 and includes an upper portion 36 and a lower portion 38 attached together at a threaded portion 40. Line 22 is connected to an inlet 42 within the upper portion 36 by a screwon fitting (not shown). Line 26 is connected to an outlet 46 within the lower portion 38 by a screwon fitting (not shown). A strainer 50 is supported within inlet 42 to trap foreign particles.

An orifice plug 52 is attached to the upper portion 38 of the expansion valve 24 between inlet 24 and outlet 46. Plug 52 has a restricted passageway or orifice 54 which fluidly interconnects the inlet 42 and the outlet 46 of expansion valve 24. High pressure liquid refrigerant from inlet 42 passes through orifice 54 and expands into a chamber 56 adjacent outlet 46. The expanded low pres- Sure liquid refrigerant then passes through outlet 46 into line 26 and hence into evaporator 28. A valve element 58 within chamber 56 is biased by a spring 60 against the bottom face of orifice plug 52 to regulate the expansion rate of liquid refrigerant through orifice 54. More particularly, valve 58 includes a cylindrical central portion 62 and three radially extending arms 64. An end surface 66 on valve 58 contacts the end of orifice plug 52 to vary the restriction through orifice 54. A spring 60 within chamber 56 normally biases valve 58 upward against orifice plug 52 to block orifice passageway 54. The upper end of spring 60 is positioned centrally against the bottom end of valve 58 by a washer 68. The lower end of spring 60 is centrally positioned within chamber 56 by a raised rib 70 formed around the upper end of outlet 46.

The end surface 66 of valve 58 is moved out of contact from the end of orifice plug 52 by pins 72 (two of which are shown) which reciprocate within bores 74 in the upper portion 36 of the expansion valve 24. The lower ends of the pins 72 contact arms 64 of valve 58. The upper ends of the pins 72 contact a disc 76. A diaphragm 78 which is affixed to the upper portion 36 of valve 24 contacts the disc 76 for relative movement therewith. Diaphragm 78 is held within the upper portion 36 of valve v24 at its outer edge by an end cover 80. The

diaphragm 78 divides the space between end cover 80 and the upper portion 36 into an upper chamber 82 and the lower chamber 84. Pressure forces in chamber 82 and 84 tend to move the diaphragm 78 in a downward or an upward direction respectively. Movement of the diaphragm in turn forces the disc 76, pins 72 and the valve 58 upward or downward. The movement of valve 58 controls the expansion rate of high pressure liquid refrigerant from the inlet 42 through the orifice passage 54 into the outlet 46.

A capillary tube or power element 86 is attached in heat transfer relationship to the evaporator outlet 30 to sense refrigerant temperature (see FIG. 1). The power element 86 is fluidly communicated with upper chamber 82 by a tube 88 attached to one end to end cover 80. The power element 86, tube 88, and chamber 82 is filled with a compressible gas such as carbon dioxide whose pressure is variable in response to the temperature sensed by power element 86 at the evaporator outlet. The pressurized gas acts upon diaphragm 78 to move the disc 76, pins 72, and valve 58 within the expansion valve 24 to regulate the expansion rate of refrigerant flowing from orifice 54. Thus when an excessive temperature is sensed by power element 86, pressure within the upper chamber 82 increases and the diaphragm 78 opens orifice 54 to supply evaporator 28 with more liquid refrigerant. Conversely, when the temperature condition sensed by power element 86 is abnormally low, the pressure in chamber 82 decreases which permits spring 60 and valve 58 to close orifice 54 and to reduce the supply of liquid refrigerant to the evaporator 28.

The throttling valve 32 maintains the evaporator outlet pressure above a predetermined minimum level which prevents the evaporator temperature from falling below freezing and ice from forming on the evaporator. Throttling valve 32 maintains the predetermined minimum pressure within the evaporator 28 by regulating the flow of refrigerant vapor from the evaporator. During normal operation of the air-conditioning system, the evaporator outlet pressure is relatively high and the throttling valve 32 is open. However, when the evaporator 28 is subjected to a relatively light heat load, the throttling valve will close periodically to maintain pressure within the evaporator.

The throttling valve 32 includes an inlet portion 90, an intermediate portion 92 composed of joined lower and

upper tubes

94, 96 and an outlet portion 98 serially joined together. The inlet portion defines an inlet port 100 which is adapted to be connected to the evaporator outlet line 30 by a fluid-tight connection. The outlet portion 98 defines an outlet port 102 which is adapted to be connected to suction line 34 by a fluid-tight connection.

Tubes

94 and 96 are joined intermediately at 104 in a fluid-tight manner to define an interior flow space 106. The lower end of the intermediate portion 92 is joined to the inlet portion 90 at 108 in a fluid-tight manner and the upper end of intermediate portion 92 is joined to the outlet portion 98 at 110 in a fluid-tight manner. A valve cylinder 112 is supported at a lower end 114 within the inlet portion 90. A spring 116 in chamber 106 is compressed between the upper tube 96 and the cylinder 112 to bias the cylinder within the inlet portion 90. An annular seal 118 is compressed between the lower end 114 of cylinder 112 and the inlet portion 90 to prevent fluid leakage therebetween.

The valve cylinder 112 has an axially directed fluid passage 120 within its lower end 114. Radially extending outlet ports 122 in cylinder 112 fluidly communicate passage 120 with the flow passage 106 within the intermediate portion 92. Thus, a fluid pathway extends from inlet port 100 through fluid passage 120, outlet ports 122 and passage 106 to the outlet port 102. End 114 of valve 112 includes a thin walled impact plate 124 having a plurality of inlet holes 126 therethrough. Plate 124 absorbs fluid impact on valve 112 caused by refrigerant flowing through the inlet port 100 into fluid passage 120.

A reciprocal piston 128 moves within passage 120 to regulate the flow of refrigerant through outlet ports 122. An upper end 130 of piston 128 extends into an interior space within the cylinder 112. An annular seal 132 supported around the periphery of the portion 130 divides this interior space into a variable volume power chamber 134 and a variable volume control chamber 136. A spring 138 in control chamber 136 presses the piston 128 downward against the end 114 of cylinder 112. While in the aforedescribed downward position, the outlet ports 122 are blocked by piston 128 to block refrigerant flow through the throttling valve 32.

When evaporator outlet pressure exceeds a predetermined minimum level, piston 128 is moved upward within passage 120 to unblock outlet ports 122 by pressure against the piston 128 in opposition to the force of spring 138. Evaporator outlet pressure acts against the portion of the piston 128 which is within passage 120 and against the peripheral portion of the piston within the power chamber 134. Pressure is admitted from passage 120 to the power chamber 134 through a port 140, a channel 142 and a cutout 144' in portion 130 of piston 128. A screen 146 in the lower end of piston 128 filters foreign particles which could clog port 140 or channel 144.

A stable pressure is maintained within control chamber 136 at a predetermined level to aid spring 138 in biasing valve 128 into a closed position. The predetermined pressure also acts as a standard against which pressure in chamber 134 is compared. A bleed hole 148 interconnects the power chamber 134 with the control chamber 136 to continuously admit evaporator outlet pressure into the control chamber 136. The pressure admitted through bleed hole 148 is reduced to a predetermined pressure level by regulated leakage into outlet port 102. More particularly, the pressure control mechanism includes a bellows chamber 150 which is formed by a cup 152 having a peripheral edge flange 154 pressed against the upper end of cylinder 112 by the spring 116. Spring 116 also holds a base plate 156 against the end of cylinder 112 to divide control chamber 136 from bellows chamber 150. A gasket 158 is compressed between tthe cylinder 112 and edge flange 154 to prevent fluid leakage therebetween. A port 160 in the base plate 156 interconnects the control chamber 136 with the bellows chamber 150. To maintain a predetermined pressure level in control chamber 136, pressure is leaked through port 160, into bellows chamber 150 and into the outlet port 102 through a bleed tube 162 in the upper end of cup 152.

Pressure leakage through bleed tube 162 is controlled by a needle valve 164 supported on a valve base 166. The

needle valve 164 seats against the lower end of the bleed tube 162 to regulate pressure leakage therethrough. Valve base 166 is attached to the end of a brass bellows 168. A spring 170 within the interior of the bellows 168 normally seats needle valve 164 against the lower end of bleed tube 162. Another spring 172 in bellows chamber normally opposes spring and tends to unseat needle valve 164 from bleed tube 162.

The lower end of bellows 168 is secured to an end plate 174 by a fluid tight connection. End plate 174 is attached to the base plate 156. Before final assembly of the throttling valve 32, the bellows 168 is evacuated through a tube 176 which is thereafter sealed at its exterior end. The pressure within the bellows 168 is reduced to a nearly perfect vacuum or zero pressure which serves as a reference in establishing the predetermined control chamber pressure level pressure.

During normal operation of the air conditioning system, the heat load on evaporator 28 is suflficient to maintain expansion valve 24 open. More particularly, a relatively large heat load produces an evaporator outlet pressure sufficient to cause piston 128 of the throttling valve 32 to move upward against spring 138 and to unblock port 122 to allow the passage of refrigerant. During this period of operation, pressure in the power chamber 134 may greatly exceed the predetermined minimum evaporator pressure necessary to prevent formation of frost on the evaporator.

It has been discovered that a minimum evaporator outlet pressure of approximately 29 p.s.i. is desirable. The regulated pressure in control chamber 136 is maintained at a level somewhat "below 29 p.s.i. dependent, of course, on the strength of

springs

170, 172 selected. The proper .control chamber pressure to close piston 128 at an evaporator outlet pressure of 29 p.s.i. is a function of the strength of spring 138. Thus with proper selection of

springs

138, 170 and 172, the piston 128 can be made to close ports 122 at an evaporator outlet pressure of 29 p.s.i.

A compressor cooling problem is caused by the closing of throttle valve 32. When the throttle valve 32 is closed, a balanced pressure-temperature condition is established across the evaporator. Under these conditions, equal pressures in chamber 82 and chamber 84 of the expansion valve 24 cause the expansion valve to close thus blocking refrigerant flow through the evaporator. Sustained blockage of refrigerant flow is undesirable because cooling of the compressor 10 is dependent upon refrigerant leakage through the throttling valve 32 and with expansion valve 24 closed no refrigerant is admitted into the evaporator for leakage through the throttling valve. To alleviate this problem an equalizer line 178 extends from the lower chamber 84 of expansion valve 24 to the passage 106 of the throttling valve 32. An inlet fitting 182 connects the equalizer line with passage 106. The equalizer line 178 transmits the fluid pressure in passage 106 to the lower chamber 84 of expansion valve 24. While the throttling valve 32 is closed, the pressure in passage 106 which is transmitted by an equalizer line 178 to chamber 84 is relatively low. This low pressure draws diaphragm 78 downward and opens the orifice 54 to supply the evaporator with liquid refrigerant. This refrigerant subsequently leaks through throttling valve 32 and reaches the compressor 10 for cooling.

The aforedescribed cooling method is inefficient, however, since considerable energy is expended in circulating refrigerant when the actual heat load on the evaporator is low. Since cooling of the compressor 10 is required only under extreme conditions when their temperature exceeds a predetermined maximum, it is desirable to inactivate the effects of the equalizer line at all times except under extreme conditions. The air-conditioning system then operates more efficiently by reducing the period of time during which refrigerant is admitted to the evaporator while the throttling valve 32 is closed.

To inactivate the equalizer line' 178, a normally closed thermally actuated valve is located in equalizer line 178. Valve 184 is opened by a temperature responsive switch 186 which is in heat transfer relationship with discharge line 16. Switch 186 may be a conventional bimetal type which closes upon sensing a predetermined maximum temperature. When switch 186 closes, a circuit is completed through a conductor 188, a battery 190, a resistance element within valve 184 and conductor 191 to open the valve.

The thermally actuated

valves

192 and 194 shown in FIGS. and 6 are suitable in the system shown in FIG. 1. Valve 192 in FIG. 5 consists of a housing 196 enclosing a hollow interior and a fiuid passage 198. The lower end of a valve stem 200 projects into passage 198 to normally block refrigerant flow therethrough. The upper end of valve stem 200 projects into the hollow interior of the valve and is attached to a piston 202. Piston 202 divides the hollow interior of valve 192 into a silicon filled chamber 204 and a spring chamber 206. A spring 208 within spring chamber 206 presses against the piston 202 to normally position valve stem 200 within passage 198. The spring chamber 206 is enclosed by an end cover 210 which is fastened to the valve housing 196 by a spun-over portion 212.

An electric resistance heater 214 within the silicon filled chamber 204 is connected to a lead from the temperature responsive switch 186 and a lead from the battery 190, as shown in FIG. 1. When switch 186 is closed, electric current through resistance heater 214 heats the surrounding silicon which expands within chamber 204. This causes the piston 202 and attached valve stem 200 to move upward against the force of spring 208 to open flow passage 198 and equalizer line 178.

FIG. 6 illustrates a second thermally responsive valve 194 which is suitable for the system shown in FIG. 1. Valve 194 consists of a housing 216 which has a port 218, an inlet 220, and an outlet 222 for the passage of fluid through the valve. Port 218 is normally blocked by a valve element 224 held against the port by spring 226. A solid cylindrical expansion member 228 is supported on an interior wall member 230 which has flow passages 232 therethrough. The member 228 projects into port 218 and is aligned with valve element 224. An electric resistance wire heater 234 encircles the expansion member 228. Leads from the temperature responsive switch 186 and the battery are connected to the heater 234. When switch 186 is closed, a closed circuit through conductor 188, battery 190, resistance wire 234, and conductor 191 heats the expansion member 228 and causes it to unseat valve element 224. This unblocks flow port 218 and opens expansion line 178.

FIG. 2 illustrates a second method of applying the thermally responsive valves to an air-conditioning system.

The thermally responsive valve 184 is placed in heat transfer relationship with discharge line 16 and the equalizer line 178 is routed through the valve. No electrical resistance wire heater is necessary with this arrangement as heat from the discharge line 16 is directly conducted to the thermally actuated valve 184. Either valve 192, as shown in FIG. 5, or the valve 194, as shown in FIG. 6, can be utilized with this arrangement but the

wire heaters

214 and 234 are unnecessary. The operation of

valves

192 and 194 remains essentially unchanged.

It should be understood that temperature responsive switch means other than bimetallic switches are contemplated and within the scope of this invention. It should also be understood that other valves than those shown in FIGS. 5 and 6 are contemplated and fall within the scope of this invention. It should further be understood that alternate locations for the temperature responsive switch and the thermally actuated valve are within the scope of this invention and that a normally open valve requiring energy to close could be adapted to the automotive air- 8 conditioning system and still be within the scope of this invention.

While the embodiments of the present invention as herein described constitute preferred forms, it is to be understood that other forms may be adapted.

What is claimed is as follows:

1. An automobile airconditioning system comprising: a compressor having an inlet and an outlet; a condenser connected to said compressor outlet; an expansion valve connected to said condenser; an evaporator having an inlet and an outlet with its inlet connected to said expansion valve; a throttling valve connected between said evaporator outlet and said compressor inlet; said throttling valve controlling refrigerant flow through said evaporator in response to the pressure of refrigerant Within said evaporator and closing to block the refrigerant flow when the evaporator pressure falls below a predetermined minimum pressure level; said expansion valve normally regulating the expansion rate of refrigerant flowing into said evaporator in response to the temperature of refrigerant in said evaporator outlet; an equalizer line between the compressor inlet and the expansion valve; a valve normally blocking said equalizer line which opens to transmit compressor inlet pressure to said expansion valve when the temperature of refrigerant in the compressor outlet exceeds a predetermined maximum value; pressure responsive means to open said expansion valve in response to the compressor inlet pressure and whereby refrigerant subsequently passes through said expansion valve, said evaporator and said throttling valve to cool said compressor.

2. An automobile air-conditioning system comprising: a compressor having an inlet and an outlet; a condenser connected to said compressor outlet; an expansion valve connected to said condenser; an evaporator having an inlet and an outlet with its inlet connected to said expansion valve; a throttling valve connected between said evaporator outlet and said compressor inlet; said throttling valve controlling refrigerant flow through said evaporator in response to the pressure of refrigerant within said evaporator and closing to block the refrigerant flow when the evaporator pressure falls below a predetermined minimum pressure level; a fluid filled power element in heat transfer relationship to said evaporator outlet and fluidly connected to said expansion valve for transmitting fluid pressure to said expansion valve in response to the temperature of refrigerant within said evaporator outlet; said expansion valve normally regulating the expansion rate of refrigerant flowing into said evaporator in response to the action of the fiuid pressure on a diaphragm within said expansion valve; an equalizer line between the compressor inlet and said expansion valve; a normally closed valve blocking said equalizer line; said equalizer line valve opening to transmit compressor inlet pressure against said diaphragm when the temperature of refrigerant in said compressor outlet exceeds a predetermined maximum value and whereby the expansion valve is opened and refrigerant subsequently passes through said expansion valve, said evaporator and said throttling valve to cool said compressor.

3. The automobile air-conditioning system as set forth in claim 2; said equalizer line valve including a variable volume chamber filled with an expandable fluid; an electric resistance heater within said chamber; circuit means including a temperature responsive switch in heat transfer relationship to said compressor outlet to energize said electric resistance heater; an interconnected piston and valve element movable by expandable fluid to open said equalizer line.

4. The automobile air-conditioning system as set forth in claim 2; said equalizer line valve including an expansion member adjacent a normally closed valve element; an electric resistance heater around said expansion member; circuit means including a temperature responsive switch in heat transfer relationship with said compressor outlet to energize said electric resistance heater and heat said expansion member to cause it to expand against said valve element and open saidvalve.

5. The automobile air-conditioning system as set forth in claim 2; said equalizer line valve being in heat transfer relationship to said compressor outlet and including a variable volume chamber filled with an expandable fluid; an interconnected piston and valve element movable by said expandable fluid to open said equalizer line.

6. The automobile air-conditioning system as set forth in claim 2; said equalizer line valve being in heat transfer relationship with said compressor outlet and including an expanson member adjacent a normally closed valve References Cited UNITED STATES PATENTS 3,084,521 4/1963 Schlotterbeck 62-217X 10 MEYER PERLIN, Primary Examiner US. Cl. X.R.