US3831391A

US3831391A - Apparatus for testing the operation of the defrost switch in an air conditioning unit

Info

Publication number: US3831391A
Application number: US00319820A
Authority: US
Inventors: P Blomstrand
Original assignee: ACF Industries Inc
Current assignee: ACF Industries Inc
Priority date: 1972-12-29
Filing date: 1972-12-29
Publication date: 1974-08-27
Anticipated expiration: 1991-08-27

Abstract

The present invention is an improvement in air conditioning system and comprises apparatus for testing the defrost switch in the air conditioning system. The apparatus comprises a pressure reservoir, means for filling the reservoir with fluid pressure, a pressure gauge, conduit means connecting the reservoir with the pressure gauge and with the defrost switch, and means such as a light or horn indicating successful operation of the defrost switch. Successful operation of the switch is clearly indicated by the light or horn even in noisy environments, and the pressure at which the switch operates can be read on the pressure gauge.

Description

Unlted States Patent 1 91 [111 3,831,391

Blomstrand Aug. 27, 1974 [54] APPARATUS FOR TESTING THE 2,968,275 l/1961 Spiro 62/128 OPERATION OF THE DEFROST SWITCH IN 3,106,833 10/ 1963 Russell 324/28 R X 3,359,749 12/1969 Howland et al.. 62/140 AN AIR CONDITIONING UNIT 3,486,241 12/1969 Coyle 6161 34/54 x [75] Inventor: Paul R. Blomstrand, St. Louis Y, Primary ExaminerWilliam F. ODea Assistant Examiner-Peter D. Fer son 73 A ACF 1 sslgnee lgg f ncorporated New Attorney, Agent, or FirmHenry W. Cummings 1 pp 319,820 The present invention is an improvement in air conditioning system and comprises apparatus for testing the 52 us. c1 62/125, 62/126, 73/4 R, defrost Switch in the ah conditioning System The 1 324/28 R paratus comprises a pressure reservoir, means for fill- 51 1m. (:1 F25b 49/00 ing the reservoir with fluid Pressure, a Pressure gauge, [58] Field of Search 62/126, 127 128, 131 conduit means connecting the reservoir with the pres- 62/140 124; 73/4 R; 324/28 R sure gauge and with the defrost switch, and means such as a light or horn indicating successful operation [56] References Cited of the defrost switch. Successful operation of the UNTED STATES PATENTS switch is clearly indicated by the light or horn even in noisy environments, and the pressure at which the 73/4 R Switch Operates Canbe read o the pressure gauge e 2.490.821 12/1949 Leonard 73/4 R 24 Claims, 3 Drawing Figures PAIENTEB All327|914 lllllill FIG. I.

APPARATUS FOR TESTING THE OPERATION 'OF THE DEFROST SWITCH IN AN AIR CONDITIONING UNIT BACKGROUND OF THE INVENTION This invention relates to testing apparatus for air conditioning systems, particularly air conditioning systems mounted on railroad cars, as described, for example, in US. Pat. Nos. 3,486,241 and 3,694,925, assigned to the assignee of the present application, and to refrigerator cars utilizing an air conditioning system. The test system of the present invention is also applicable to air conditioned overland trucks and generally to industrial air conditioning systems.

In nearly all air conditioning systems some defrost must occur from time to time. In many air conditioning systems the defrost cycle begins when the pressure differential across the evaporator coil reaches a desired level. This pressure differential is utilized to activate a switch which turns off a fan causing air to pass through the evaporator or may close a door preventing air to pass over the evaporator. The switch also may activate a heater to melt ice which may have accumulated during the previous cooling and dehumidifying cycle.

It is very important that this switch operate properly; otherwise the air conditioning unit may freeze up, large amounts of ice may develop on the tins of the evaporator and shut off all passageways through the evaporator. In this event, there is no air conditioning provided to the lading and lading damage is likely to result, particularly in the case of perishable lading. The air conditioning unit also may be damaged. In noisy installation environments it is particularly difficult to determine if the switch is operating properly because it is often difficult to hear the switch click.

Therefore it is desirable that there be a reliable test to insure that this switch is operating properly.

It therefore is an object of the present invention to provide a test apparatus to determine if the defrost switch in an air conditioning unit is operating properly.

It is another object of the present invention to provide a test apparatus for testing the defrost air switch in which the pressure at which the switch operates .can be determined with close accuracy.

It is another object of the present invention to provide a test apparatus which will clearly indicate the proper operation of the defrost switch in noisy environments.

It is another object of the present invention to provide a defrost air switch apparatus which is inexpensive and simple to manufacture and assemble.

Other objects will be apparent from the following description and drawings.

SUMMARY OF THE INVENTION The present invention is an improvement in air conditioning system, and comprises apparatus for testing the defrost switch in the air conditioning system. The apparatus comprises a pressure reservoir, means for filling the reservoir with fluid pressure, a pressure gauge, conduit means connecting the reservoir with the pressure gauge and with the defrost switch, and means such as a light or horn indicating successful operation of the defrost switch. Successful operation of the switch is clearly indicated by the light or horn even in noisy installation environments, and the pressure at which the switch operates can be read on. the pressure gauge.

THE DRAWINGS FIG. I is a schematic view of an air conditioning system to which the testing apparatus of the present invention is applicable;

FIG. 2 is a schematic illustration of the defrost air switch with the air switch testing apparatus of the present invention attached thereto;

FIG. 3 is a schematic illustration of the defrost air switch showing the position of a movable member at the time the defrost cycle is initiated.

DETAILED DESCRIPTION The cooling and dehumidifying portion of a conventional air conditioning system is the evaporator. In FIG. 1, the evaporator 10 is provided with a coil 12 for circulating refrigerant fluid. The coil 12 may be provided with means for insuring contact with the air for heat exchange purposes, for example, a plurality of fins 14. The evaporator is further provided with one or more air inlets l6 and air outlets 18. Air to be cooled and dehumidified passes through the inlet 16 and contacts some of the heat exchange means 14. The liquid passing through the coil 12 cools the air and results in the condensation of water on the fins and on the coil. During this process the the liquid refrigerant is heated and at the end portion of the evaporator becomes a gas. One of the most common refrigerants comprises monofluero, trichloro methane (MFf CM). The gaseous refrigerant exists from the evaporator through one or more conduits 20 and passes to a compressor 22. In the compressor the gas is compressed and the temperature of the gas is increased. From the compressor the gas passes through a conduit(s) 24 to a condensor 26 wherein the gas is cooled to the liquid state usually with substantially no change in pressure. The liquefied refrigerant then passes through a conduit(s) 27 to an expansion valve(s) 28 wherein the temperature and pressure of the liquid are reduced. After passing through the expansion valve, the refrigerant passes through a conduit(s) 30 into the evaporator coil 12 and the cycle is repeated. This basic air conditioning cycle is wellknown in the art.

The air conditioning system continues to function in the described manner until the temperature of the refrigerant sufficiently cools the fins that they reach a temperature of 30 to '3 3 F. wherein condensed water begins to freeze on the heat exchange means (fins) and on the coil(s). As freezing progresses and more and more ice builds up on the heat exchange means the pressure drop across the evaporator increases because the ice has the effect of cutting the flow, reducing the passages through which the air can pass. At the same time, if the system is properly designed, the air being circulated through the system is substantially cooled and dehumidified at this time. Most systems are set up such that when the pressure drop across the evaporator reaches a certain value a switch is activated to alter the air conditioning cycle. A conduit or tube 32 is generally provided from the exit end of the evaporator to the front end of the evaporator to a switch indicated generally at 40. It will be understood that the switch could also be located at the exit end of the unit and the conduit 32 be a bleed on the inlet air pressure. By way of example, in one air conditioning system, when the air temperature is about 55F. the pressure drop across the evaporator is approximately one inch of water. However, when the temperature of the fins is approximately 30 to 33F, the pressure drop soon reaches a value of around 1.25 inches of water. While these numbers vary considerably from unit to unit, this is the type of spread which is often observed in air conditioning units and does indicate that this pressure drop is a useful means of turning off the air conditioning cycle and initiating a defrost cycle.

The switch 40 is shown in enlarged view in FIG. 2. The switch comprises a housing 42 having an opening 44 for a pressure conduit from the inlet side of the evaporator and a second conduit 46 for inlet of pressure from the outlet side of the evaporator. Also mounted within the housing 42 is a movable member, for example a diaphragm 48. A resilient means such as one or more springs 50 is affixed to the diaphragm by any conventional means, such as a screw 52 and the other end is affixed to a lever 54 by similar suitable means. Lever 54 is pivoted about a point 56 and has mounted at the other end thereof a contact 58. Mounted adjacent to movable contact(s) 58 is a fixed contact(s) 60.

In the operation of the switch 40 the inlet pressure of the air going into the evaporator is constantly applied to the upper surface in FIG. 2 of the diaphragm 48. The outlet pressure of the evaporator air is applied to the lower surface of the diaphragm 48. The spring constant of the resilient means (i.e. spring 50) is biased to urge diaphragm 48 upward in FIG. 2.

The inlet pressure P,- acting on the movable member (i.e. diaphragm 48) is tending to pivot lever 54 about pivot point 56. This action is resisted by spring 50 and outlet pressure P acting on the lower side of the diaphragm. Thus when the outlet pressure P drops to a certain level, there is no longer sufficient resistance to the application of inlet pressure P,, and the lever 54 pivots about the point 56 and contact 58 engages contact 60 as shown in FIG. 3. When this occurs, a relay(s) 62 is activated.

Relay(s) 62 is conventional in construction including a coil 64 and a magnet 66 and a plurality of

contacts

67, 68 and 69. One set of contacts, for example, 67 may turn off the fan 70 used to move the air through the evaporator or close the air inlet(s) to the evaporator. Another contact, for example, 68 may activate a heater 72 which acts to melt the ice accumulated on heat exchange fins 14.

The defrost cycle will remain on until the thermal switch 74 (FIGS. 1 and 2 comprising a thermometer or thermocouple) registers a sufficiently high temperature to deactivate the contact 76. Switch 74 will then insure that contacts 58 and 60 are parted and that lever 54 returns to the position shown in FIG. 2. At the same time, relays 62 will activate fan 70 so that air will then again flow through the evaporator and heater 72 turned off. The air conditioning cycle will then be repeated.

The test apparatus of the present invention is indicated generally at 80 and comprises a pump 82 in communication with a reservoir 84 having a valve 83 therebetween. The reservoir by means of conduit 86 is in communication with a valve 88. By means of the valve 88, the pressure from reservoir 84 is applied through conduit 90 to pressure gage 92 and through conduit 94 to inlet 44 and diaphragm 48. Pressure gauge 92 may be of conventional construction, for example, as described in US. Pat. No. 2,772,837. Thus, the pressure which is applied to diaphragm 48 through conduit 94 may be read on gauge 92. If the switch 40 is working properly at the desired pressure differential, the pressure differential between the two sides of the diaphragm will cause lever 54 to pviot about point 56 and the contacts 58 and will close. As shown further in FIG. 2, a switch indicating means 96 is connected by means of

lead wires

97 and 98 to output contacts 61 and 63. A battery 99 or other suitable power source may also be included in the circuit. If the pressure differential readable on gauge 92 causes the switch 40 to operate indicating means 96 will so indicate. For example, indicating means 96 may comprise a light. If the light does not flash or if it flashes at a point either above or below the designed pressure differential, it will be apparent that adjustments in the switch 40 are required. Alternatively a sounding device, such as a horn, could be utilized as the indicating means.

It will be apparent that the present testing apparatus is considerably improved over the prior art method of blowing into a water monometer and listening for the switch to click. Accuracy of i0.5 inches of water is obtainable with this prior art method if the operator were able to hear the click. Often in a field installation the power source for the air conditioning unit, such as diesel engines and/or generators, make sufficient noise that hearing the click is difficult.

With the test apparatus of the present invention improved accuracy is obtained in testing the defrost switch in the area of i 0.1 inches of water or a factor of roughly five.

What is claimed is:

1. Apparatus for testing a defrost switch in an air conditioning installation comprising:

a reservoir for containing fluid pressure; means for filling said reservoir with fluid pressure; conduit means connecting the reservoir with a pressure gauge and adapted to connect said reservoir with a movable member in an air conditioning system which activates a defrost switch; and indicator means adapted to be connected to said defrost switch indicating the operation of said switch even in noisy environments.

2. Apparatus according to claim 1 wherein a resilient means urges said movable member out of engagement with contacts in said defrost switch.

3. Apparatus according to claim 1 wherein a first conduit connects said reservoir with said movable member and a second conduit connects said reservoir to said pressure gauge.

4. Apparatus according to claim 3 wherein a valve is provided between said reservoir and a point where said first and second conduits join.

5. Apparatus according to claim 1 wherein said means for filling said reservoir comprises a pump.

6. Apparatus according to claim 2 wherein said movable member is a flexible diaphragm.

7. Apparatus according to claim 3 wherein the means indicating successful operation of said switch is a light.

8. Apparatus according to claim 3 wherein the means indicating successful operation of said switch is a horn.

9. in an air conditioning system in which the air conditioning unit has a cooling and dehumidifying cycle and a defrost cycle and a switch activates the'defrost cycle, the improvement comprising apparatus for testing the operation of said switch including a reservoir for containing fluid pressure; means for filling said reservoir with fluid pressure; conduit means connecting said reservoir with a movable member in said air conditioning system which activates said defrost switch and with a pressure gauge; and means connected to said defrost switch indicating the operation of same.

10. In an air conditioning system according to claim 9 wherein a resilient means urges said movable member out of engagement with contacts in said defrost switch.

11. in an air conditioning system according to claim 9 wherein a first conduit connects said reservoir with said movable member and a second conduit connects said reservoir to said pressure gauge.

12. ln an air conditioning system according to claim 11 wherein a valve is provided between said reservoir and a point where said first and second conduits join.

mounted thereon in which the air conditioning unit has a cooling and dehumidifying cycle and a defrost cycle and a switch activates the defrost cycle, the improvement comprising apparatus for testing the operation of said switch including a reservoir for containing fluid pressure, means for filling said reservoir with fluid pressure, conduit means connecting the fluid pressure with a movable member in said air conditioning system which activates said defrost switch and with a pressure gauge, and means connected to said defrost switch indicating the operation of same.

18. In a railway car according to claim 17 wherein a resilient means urges said movable member out of engagement with contacts in said defrost switch.

19. In a railway car according to claim 17 wherein a first conduit connects said reservoir with said movable member and a second conduit connects said reservoir to said pressure gauge.

20. In a railway car according to claim 19 wherein a valve is provided between said reservoir and a point where said first and second conduits join.

21. In a railway car according to claim 17 wherein said means for filling said reservoir comprises a pump.

22. In a railway car according to claim 18 wherein said movable member is a flexible diaphragm.

23. In a railway car according to claim 19 wherein the means indicating successful operation of said switch is a light.

24. in a railway car according to claim 19 wherein the means indicating successful operation of said switch is a horn.

Claims

1. Apparatus for testing a defrost switch in an air conditioning installation comprising: a reservoir for containing fluid pressure; means for filling said reservoir with fluid pressure; conduit means connecting the reservoir with a pressure gauge and adapted to connect said reservoir with a movable member in an air conditioning system which activates a defrost switch; and indicator means adapted to be connected to said defrost switch indicating the operation of said switch even in noisy environments.

9. In an air conditioning system in which the air conditioning unit has a cooling and dehumidifying cycle and a defrost cycle and a switch activates the defrost cycle, the improvement comprising apparatus for testing the operation of said switch including a reservoir for containing fluid pressure; means for filling said reservoir with fluid pressure; conduit means connecting said reservoir with a movable member in said air conditioning system which activates said defrost switch and with a pressure gauge; and means connected to said defrost switch indicating the operation of same.

12. In an air conditioning system according to claim 11 wherein a valve is provided between said reservoir and a point where said first and second conduits join.

13. In an air conditioning system according to claim 9 wherein said means for filling said reservoir comprises a pump.

14. In an air conditioning system according to claim 10 wherein said movable member is a flexible diaphragm.

15. In an air conditioning system according to claim 11 wherein the means indicating Successful operation of said switch is a light.

16. In an air conditioning system according to claim 11 wherein the means indicating successful operation of said switch is a horn.

17. In a railway car having an air conditioning system mounted thereon in which the air conditioning unit has a cooling and dehumidifying cycle and a defrost cycle and a switch activates the defrost cycle, the improvement comprising apparatus for testing the operation of said switch including a reservoir for containing fluid pressure, means for filling said reservoir with fluid pressure, conduit means connecting the fluid pressure with a movable member in said air conditioning system which activates said defrost switch and with a pressure gauge, and means connected to said defrost switch indicating the operation of same.