EP1169187A1

EP1169187A1 - Control system for mobile air conditioning apparatus

Info

Publication number: EP1169187A1
Application number: EP00905834A
Authority: EP
Inventors: Rene F. Bascobert
Original assignee: TRANSNAT ENTPR Inc; Transnational Enterprises Inc
Current assignee: TRANSNATIONAL ENTERPRISES Inc
Priority date: 2000-01-31
Filing date: 2000-01-31
Publication date: 2002-01-09
Also published as: JP2003520732A; AU2000227455A1; CA2315775A1

Abstract

A control system for mobile air conditioning systems for regulating the rate at which the system compressor (10) or clutch (14) is cycled between operational and decreased refrigerant flow, by selectively regulating the response time of certain system control signals to flow demand changes including de-icing control, from interactions between de-icing control and flow control valves, as well as system overall control. Upon the detection of an icing condition, the response of the control system is delayed to a degree to control the rate at which the capacity of the compressor (14) can be cycled within design limits. The delay feature allows the differential used in differentiating between icing and non-icing conditions to be significantly reduced so as to improve the performance of the air conditioning system. Icing conditions can be determined by sensing the condition of the refrigerant flow from the evaporator (18).

Description

Control System For Mobile Air Conditioning Apparatus

This invention relates to mobile air conditioning systems controls for controlling compressor cycling, in particular while in the evaporator de-icing mode, for increased system performance.

The design criterion of mobile air conditioning systems requires that the air conditioning systems be designed to operate as efficiently as possible over a wide variety of environmental and operating conditions in a manner so as not to detrimentally impact the capability of the equipment to properly perform, particularly the compressor or its clutch, as environmental and operation conditions change. One of the demands on operation of the compressor or its clutch is created by mobile air conditioning systems evaporator de-icing control. Evaporator icing is caused when the evaporator temperature is dropped to a level, that when air is blown through the evaporator, the humidity in the air causes ice crystals to form on the fins and tubing within the evaporator. If this continues for an extended period of time, the ice so formed will impeded the flow of air through the evaporator, reducing the cooling capacity of the air conditioning system and in the extreme, if sufficiently entirely iced over, essentially cutting off most of the air flow, thereby effectively incapacitating the air conditioning system.

In known mobile air conditioning systems such as those included in automobiles, trucks, buses, etc., presently include a temperature or pressure sensor at the output of the evaporator to detect when the evaporator is operating at a condition that is likely to cause icing. When the icing condition is sensed, the sensor reduces the compressor refrigerant flow capacity by operating a clutch relay, or switch, to deactivate the compressor clutch and thereby stop refrigerant flow until the sensor detects the selected non-icing condition. Such mobile air conditioning systems are usually driven by the vehicle, engine through an electrically operated clutch. The clutch is initially activated when the air conditioning system is turned on, and then turned on and off by the vehicle air conditioning system temperature control system to maintain the vehicle at the desired temperature. In the later vehicle models, the evaporator icing sensor is connected to a vehicle computer that controls the activation and deactivation of the clutch.

It has been found that the higher the humidity of the atmosphere, more likely that icing can occur in the evaporator. Hence, mobile air conditioning systems are more susceptible to icing in the more humid, locations, which can be considered as the "worse case" for design purposes. As in most mechanical devices, mobile air conditioning systems, clutches have design limits as to the number of times the clutch can be cycled on and off over a period of time with out causing deterioration or breakdown. In the case of automobile air conditioning systems, it is recommended that the compressor clutch should cycle on and off no more than six times a minutes. Hence, it is important that the design of mobile air conditioning systems operates efficiently over a wide range of environmental and operating conditions, without evaporator icing, and without causing excessive cycling of the compressor clutch.

The known present approach is to maintain a balance between evaporator de-icing control and compressor cycle rate is to include a large differential in the icing detector sensor between selected non-icing and icing conditions. The large sensor differential was selected was that needed for worse case conditions (i. e. expected worse case humidity, temperature, etc. conditions). The sensor was set so that the selected large differential, along with the response time of the air conditioning system, assures that de-icing system clutch cycling demands are within recommended cycling design limits at worse case conditions. For example, in some models of automobiles the icing condition is selected at 25 psi., while the non-icing condition is selected at 45 psi, (system reset condition), a significant differential of 20 psi. Although this arrangement was found to be a satisfactory to prevent evaporator icing in mobile air conditioning systems for worse case conditions, this large differential penalizes the performance of the air conditioning system in other than worse case conditions by keeping the compressor in the off condition over a wider range of the temperatures than needed. For example, if the compressor is shut off at the icing condition of 25 psi., the entire air conditioning system remains shut off until the preset differential high limit of 45 psi. is reached, a significant dead time required for the worst case operation. Since such large differential was selected for the worse case condition, the same large differential exists for all other operating conditions, despite the fact that the large differential is not needed and thereby unnecessarily detrimentally impacts the performance of the system under the large majority of operating conditions by keeping the system shut down longer than needed. It would therefor be advantageous if the differential detection range between the icing and non-icing conditions could be reduced to improve the overall performance of the air conditioning system while still not exceeding the recommended clutch cycling rate.

Further, the use of a pressure sensing compressor clutch deactivating system of the prior art was found to be undesirable in mobile air conditioning systems using a temperature sensitive refrigerant control valve (that controls the refrigerant flow through the system. Such temperature sensitive control valves are connected in the output line of the evaporator to detect the evaporator output temperature and control the system refrigerant flow as a function of evaporator output superheat. The temperature sensing mechanism of the control valve is inherently slow in its reaction both in its refrigerant flow restricting and increasing flow modes. With a pressure sensing evaporator icing control included in such system, it was found that when the control valve cuts back refrigerant flow and an icing condition is simultaneously sensed, the combination of the response times of the operation of the valve and the icing control system interact to cause the compressor clutch to rapidly cycle off and on several times before the system is stabilized. This clutch cycling not only is detrimental to the life of the clutch but was found to be annoying to the vehicle operator. It would therefor be advantageous to be able to include an evaporator deicing control system in a mobile air conditioning systems using a temperature controlled control valves that would be operable in such systems and still avoid the repetitive cycling of the compressor clutch due to valve and icing system interaction.

An obj ect of the present invention is to provide compressor flow control arrangement for controlling compressor or clutch cycling in mobile are condition systems that provides for the use of the evaporator deicing control arrangement that has a significantly reduced range between icing and non-icing determinations so as to improve the overall system performance while rnaintaining compressor clutch cycling within design limits.

The present invention includes a control system for mobile air conditioning system including an evaporator de-icing control system comprising means for determining when the evaporator is likely to be in an icing condition and when the evaporator is to be in a non- icing condition, characterized in that refrigerant flow control means for reducing the level of refrigerant flow in the system when an icing condition is determined and for resetting the refrigerant flo to the normal operate level when an non icing condition is determined, and means for controlling the time response by which the refrigerant flow control means reacts to the determination of at least one of the icing and non-icing conditions, in which the determining means is a sensor located adjacent to the evaporator so as to determine whether the evaporator is in an icing condition or in a non-icing condition. The invention also include a method for improving the performance of a vehicular air conditioning system including a compressor, a condenser, a refrigerant flow control mechanism, an evaporator, a compressor clutch in which the clutch has a designated limit on the rate at which the clutch is to be cycled, a control system for controlling refrigerant flow in the air conditioning system by actuating and de-actuating the clutch to turn the compressor on and off respectively, and an evaporator icing detector arrangement for providing an icing signal when a determination is made that the evaporator is likely to be in an icing condition and a non-icing signal when a preset determination is made that the evaporator is not likely to be in an icing condition wherein the size of differential between icing and non-icing conditions is controlled by the selection f the non-icing determination, and the sensor interacts with the control system to enable the control system to de-actuate the clutch in response to icing signals and to enable the control system to re-actuate the clutch in response to non-icing signals, characterized by delaying the control system response to at least one of the icing and non-icing signals to de-actuate or re-actuate the clutch, and setting the non-icing determination at a level so that the delay introduced in the control system controls the maximum rate at which the clutch can be cycled between actuation and de-actuation in response to the icing and non-icing signals.

The invention will now be described by way of example, with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of an orifice type of mobile air conditioning system including the evaporator icing control system;

Figure 2 is a schematic diagram of a temperature sensing control valve type of mobile air conditioning system including the evaporator icing control system;

Figure 3 is a first embodiment of an icing detection and control circuit for introducing a time delay, into the deactivation of the clutch in response to sensor evaporator icing signals, in which the sensor is connected directly in the clutch circuit and a time delay relay contacts are connected in parallel to the sensor.

Figure 4 is a second embodiment of an icing detection and control circuit for introducing a time delay, into the deactivation of the clutch in response to the sensor evaporator icing signals, in which the sensor is connected series with a clutch actuating relay that includes a time delay relay by pass circuit.

Figure 5 includes a schematic diagram of another embodiment of an orifice type mobile air conditioning system have a computer to control the air conditioning system and including the evaporator icing control system; Figure 6 included a flow diagram for modifying the software in the computer of

Figure 5 to include an overall clutch cycle control feature;

Figure 8 includes a schematic diagram of another embodiment of a temperature sensing valve controlled type mobile air conditioning system having a computer to control the air conditioning system and including the evaporator icing control system; and Figure 9 includes a flow diagram for modifying the software in a computer of Figure

8 to include a valve motion detection in the icing control system.

The mobile air conditioning system of Figure 1 includes a compressor 10 that is coupled to be driven by the vehicle engine (not shown) that powers both the vehicle and the mobile air conditioning system. In the case of an automobile air conditioning system the compressor is usually driven by a belt coupling between the engine and the compressor pulley 12. The compressor 10 is driven via a clutch 14 when activated. The speed at which the compressor 10 is rotated is a function of the speed of rotation of the vehicle engine. Hence the higher the speed or rotation of the engine, the higher the speed of rotation of the compressor, and therefor the higher the capacity of the compressor to pump refrigerant. The compressor 10 is turned on and off via the clutch 14 by the air conditioning system control system 30 as the need for air conditioning arises.

The direction of refrigerant flow through the system is illustrated by the arrows 24. A compressed high pressure gaseous refrigerant flows from the compressor 10 through a condenser 16. The purpose of the condenser 16 is to reject heat fro the air conditioning system, while at the same time condenses the high pressure gaseous refrigerant into high pressure liquid refrigerant. Air flow through the condenser 16 absorbs heat from the refrigerant. In mobile air conditioning systems the flow of air through the condenser 16 is variable and is controlled by the combination of the speed at which the vehicle is traveling, the speed at which the engine fan is rotating, and the speed at which a condenser fan (not shown) is rotating, wherein the greater the air flow there through the greater the heat rejection, and visa versa.

The high pressure liquid refrigerant flows through an orifice 20, which is of a fixed size and restricts refrigerant flow through the air conditioning system and particularly the amount of refrigerant flow through the evaporator 18. Ideally a low temperature, all Uquid refrigerant within the evaporator 18 that causes heat absorption and provides the cooling effect of the evaporator 18. A blower 21 blows air through the evaporator 18 cooling the air as it passed through the evaporator providing for vehicle cooling. The speed control (not shown) for the blower 21 can be the existing multi-speed of variable speed types. As previously mentioned above, in certain environmental conditions that the vehicles are exposed to, particularly in high humidity, the evaporator 18 has a greater tendency to ice over. In addition, the high humidity along with vehicle speed and engine speed further increases the tendency for icing. This icing of the evaporator 18 may seriously impact the efficient flow of air through the evaporator and thereby detrimentally impact the system performance.

The refrigerant flows from the evaporator 18 through an accumulator 22 back to the compressor 10. If liquid refrigerant flows from the evaporator 18, to determine if the evaporator 18 is likely to be in , or about to be, in an icing condition. The sensor of Figure 1 is illustrated as located in the refrigerant flow line of the accumulator 22, however it can be located in the flow line 23 itself. The sensor can determine if the icing conditions are likely to be present through either, temperature or pressure measurements, although pressure is preferred due its inherent quicker response time by avoiding the thermal lag usually involved in temperature sensing. If a temperature sensor is to be used, the sensor could be alternatively placed within the evaporator 18.

The mechanical limits of the clutch 14 are such that the clutch 14, or compressor, should only be cycled within its design limits or else be subject to deterioration or break down due to mechanical or electrical failures. It was because of these design limits that known the icing sensing system included an evaporator sensor with an undesirable selected large differential gap between icing and non-icing signal levels for worst case cycling conditions. This large differential was selected to create a limit on the switching cycling rate that could be applied by the icing control system to the clutch 14 at worst case cycling conditions. Since the known large sensor differential was selected for the worse case cycling conditions, the same undesirable large differential limitations are applied to all other operating conditions (non-worse case) and therefor results in an associated overall loss in system performance where the large differential is not needed.

The limitations on system performance introduced by the undesirable large sensor differential of the known icing control systems are reduced, in accordance with the invention, by contiolling the response time by which the clutch can respond to de-icing signals, by the introduction of off and/ or on delays, control switching sequences etc. This introduction of controlled response times allows for a significant reduction in icing sensor differentials between icing and non-icing detection levels that can be used without exceeding clutch or compressor cycle limits. Hence, with a reduced icing and non-icing differential, the mobile air conditioning system will operate at improved performance for all operating conditions, while though the innovative use of controlled response times trough delays or switching sequences excessive clutch cycling is avoided.

The icing detection and control circuit 26 of Figure 1 is connected in series between the air conditioning system control circuit 30 and the compressor clutch 14 circuit. The icing detection and control circuit 26 can include a sensor with a built in mechanical delay, or the delay can be created electrically as illustrated in Figures 3 and 4, or electronically, or by computer programming as illustrated in Figures 5 and 6. Whenever the sensor detects an icing condition, a delay period is created during which time the compressor clutch 14 cannot be deactivated, or activated, by the icing sensor. In accordance with one embodiment, after the delay period has run, the icing detection and control circuit 26 opens the connection to the clutch and the clutch is deactivated and the flow of refrigerant is cut off until the non-icing condition is detected. When the non-icing condition situation is detected y the sensor and after the delay has run, the circuit to the clutch 14 is again closed via the icing detection and control circuit 26 and the refrigerant flow is reactivated by the compressor 10 under the control of the air conditioning control circuit30. In accordance with another embodiment the clutch could be immediately deactivated with its reactivation delayed. Hence, is now can be seen that the limit for cycling the clutch can be controlled by a delay and now a smaller sensor differential can now be used to distinguish between the icing and non-icing modes. By reducing the icing sensor differential, the designated lower level of non-icing condition is detected sooner. This in turn provides for a shorter period of system operation sown time (a shorter period of time during which the refrigerant flow is interrupted) and therefor a correspondingly better the system performance. Therefor, in accordance with the invention, it can be seen the penalty that accompanied the undesirable known large sensor differential (set by worst case driving conditions) can now be significantly reduced while still safeguarding the cyclic operation of the clutch 14 by the use of a delaying action and/ or switching sequences.

For the purpose of simplifying the explanation of the invention, in Figures 1,2,5 and 8 the same elements in each of these Figures will have the same references numerals. The mobile air conditioning system of Figure 2 includes a temperature sensing control valve 32 instead of the orifice 20. The valve 32 detects the temperature of the refrigerant flow from the evaporator 18 to control the refrigerant flow through the air conditioning system. The evaporator icing detection and control circuit 26 is located in the flow line 37 before the valve 32, but could be located after the valve 32, or if a temperature sensor is used, within the evaporator 18. The icing sensor circuit 26 functions in the same manner as described with regard to Figure 1.

Figure 3 includes a first embodiment characterizing an icing detection and control circuit 26 for use in Figures 1 and 2. A set of normally closed contacts 41 of the icing sensor 40 are connected in series between the air conditioning system control 30 and the clutch 44 coil 45 to ground 43. A coil 47 of a delay relay 46 is connected between the contacts 41 and the coil 45 and ground. The normally open contacts 48 is of the type that continues in the activated condition for a preset period of time after being de-energized. In the non-icing mode, the sensor contacts 41 are closed allowing the clutch coil 45 to be energized by the air conditioning control 30 and the time delay relay coil 47 is also energized to close contacts 48. When the sensor 40 detects an icing condition the contacts 41 open. However, the contacts 48 of the time delay relay 46 remain closed and by pass the sensor contacts 41 for a preset period of the time delay. When the delay period of time has expired, the contacts 48 open and the clutch coil 45 is de-energized to shut off the compressor. The period of delay time selected for the relay 46 is of a duration to keep the sensor contacts 41 by passed by the contacts 48 so that the clutch 14 can not be cycled by the sensor contacts 41 beyond its design limits. With the clutch 14 disengaged, the flow of refrigerant ceases allowing the evaporator to warm up . When the sensor 40 detects the selected non-icing condition, the contacts 41 are closed to energize the clutch coil 45 and restart the flow of refrigerant, while also simultaneously energized the time delay relay 46. If the sensor contacts 41 close before the delay time of the relay 46 has expired, the delay relay 46 is re-energized and the clutch 14 remains continuously energized of an uninterrupted flow of refrigerant.

Figure 4 includes second embodiment of an icing detection and control circuit 26 for use with Figures 1 and 2. A power relay 54 is connected in series with the sensor 50 normally closed contacts 51. The relay 54 coil 56 is actuated and de-actuated in response to the closing and opening of the sensor contacts 51. The power relay normally open contacts 55 are connected between the system control 52 and the clutch 64 coil 63. The circuit of Figure 4 has the advantage of removing the sensor contacts 51 out of the high current clutch coil 64 circuit. In Figure the time delay relay 58 coil 60 is energized whenever the relay 54 is energized and the normally open contacts 62 are connected in parallel to the power relay contacts 55. Whenever the contacts 51 are opened due to the detection of an icing condition, the relay 54 is opened, but the contacts 62 continue to by pass the contacts 55 for the time delay of the time dely relay 58 preventing the de-energization of the clutch coil 63 during the time dely period. When the sensor 50 detects the preset non-icing condition, the contacts 51 are closed to energize the relay 58, the delay relay 46 and the clutch coil 60.

Although the circuits of Figures 3 and 5 provide an arrangement wherein there is a time delay introduced before the clutch can be deactivated, it should be understood that the circuits can be modified so that the clutch coil can be immediately deactivated and a time delay introduced before the clutch could be reactivated. Although the electrical control circuits of Figures 3 and 4 disclose the concept of inserting delays into the air conditioning system control with the use of sensor switch contacts and relays, it should be understood that the icing detection and control circuit 26 could as well be embodied with the use of well known solid state detectors, delay circuits and switching devices. Wit the added use of computers in mobile air conditioning system, including the evaporator icing control for the system, can be used, in accordance with the invention, to improve the performance of the system by providing the delaying action for limiting the rate at which the compressor clutch 14 can be cycled on and off.

As illustrated in Figure 5, the known vehicle computer 74 receives signals from the air conditioning control 30 to control the operation of the air conditioning system, and receives icing condition signals from an evaporator icing sensor 70. In accordance to the invention, the portion of the known computer software in the computer 74 pertaining to the energization of the clutch 14, via the clutch control circuit 72, is modified to insert time response control for limiting the cycle rate at which the clutch 14 can be turned on and off. For example, instead of responding to the icing signal from sensor 70 to immediately de- energize the clutch 14, the computer 74 is programmed to introduce a delay time to prevent the clutch 14 from being de-activated until the delay period has run or alternatively to program the computer 74 to immediately de-energize the clutch and to delay the reactivation of the clutch.

The flow diagram of Figure 6 includes a modification of the computer 74 software to include the time response contiol concept of the invention. The first step 76 of the process determines if the vehicle engine is running, while the second step 77 determines if the air conditioning system is turned on. Step 78 determines if there is a request for air conditioning from step 84 (which compares the air conditioning temperature setting with the internal vehicle temperature). If there is a request for air conditioning, the step 78 enables the clutch engage step 79 to enable the clutch relay 80 to engage the clutch 81. However if an icing condition is determined by ste 82, instead of its output being directly applied to disable the clutch (as done in the prior art, a delay step 83) is included between steps 79 and 82. The delay can be an off delay as in Figures 3 and 4, or can be an on delay wherein the seep 79 is immediately disabled and a delay is inserted in engaging the clutch. The delay is that needed to keep the clutch from cycling beyond designated limits.

The flow diagram of Figure 7 included a modification of the flow diagram of Figure 6 that includes an overall clutch cycle control feature. The step 06 continually counts the rate at which the clutch is cycled in general, and the cycle rate is compared with preset limit by the step 97. If the preset limit is exceeded, the step 97 applies a limit exceeded indication to the disengage step 98 and to the delay step 99. The delay step 99 can be an off delay or an on delay. If an off delay is used, the arrangement is such that the disengage step 98 applies a disengage designation to the clutch engage step 79 after the delay of step 99 has run, If an on delay is used that the step 98 applies the disengage immediately upon receipt of the limit exceeded status and can be re-engaged after the delay of step 99 has run. The duration of the delay is that needed to keep the clutch cycle rate within design limits.

In accordance with Figure 8, the vehicle computer 74 has been programmed to function in the same manner in response to icing signals from sensor 70 as in Figure 5. However, the computer 74 is also programmed to be responsive to signals from a motion detector 75 to prevent the repetitive cycling of the clutch 14 due to the interaction of icing control and valve flow control as mentioned above. The motion detector 75 is coupled to the temperature sensitive control valve 32 to detect valve motions of magnitudes that might cause the interactive cycling. The program of the computer 74 is modified to temporarily inhibit the computer 74 from acting on the icing signals from the sensor 70 during the motion of the valve 32 that might have other wise interacted with the icing control caused by the repetitive clutch cycling.

The flow diagram of Figure 9 includes a modification of the software of the computer 74 of Figures 6 and 8 so as to reduce the cyclic interaction between the temperature

5 controlled valve 32 and the icing sensor 70. The motion magnitude step 106 determines when the motion temperature controlled valve 32 exceeds predetermined limits and enables the motion signal generator step 107 to apply a motion designation to the interaction step 108. The interaction step 108 also receives an icing designation form the icing condition step 82. When both the icing and motion designations are present, the output of step 198 enables

10 the inhibit step 109 to inhibit the application of the icing condition control until the motion of the temperature controlled valve motion is within limit to minimize the interaction mentioned above.

A delay is inserted in the clutch control circuit for confrolling the clutch cycle rate instead of the inefficient use of the known large sensor differential . The delay can be set for

15 10 seconds so as not to exceed the design recommendation of a maximum of 6 clutch cycles per minute. Under normal condition (non-worse case condition) with the likelihood of excessive clutch cycling decreasing, the sensor icing - non icing differential can be significantly decreased, which in turn reduces s stem dead time resulting in a corresponding improvement in system performance.

20 In a more sophisticated systems using computers y which the operation of the clutch is controlled, the invention can be simply installed by replacing the known icing sensor with a sensor with a smaller differential and by programming the delay into the computer. The computer can have the added advantage of accumulating data as to the periodic and cyclic operation of the clutch, and if history allows, only insert the delay when required.

25 A control system for mobile air conditioning systems for regulating the rate at which the system compressor or clutch is cycled between operational and decreased refrigerant flow, by selectively regulating the response time of certain system control signals to flow demand changes including de-icing control, from interactions between de-icing control and flow control valves, as well as system overall control. Upon the detection of an icing condition, the response of the control system is delayed to a degree to control the rate at which the capacity of the compressor can be cycled within design limits. The delay feature allows the differential used in differentiating between icing and non-icing conditions to be significantly reduced so as to improve the performance of the air conditioning system. Icing conditions. Can be determined by sensing the condition of the refrigerant flow from the evaporator.

Claims

CLAIMS:

1. A contiol system for mobile air conditioning system including an evaporator de-icing control system comprising means for deterrruning when the evaporator is likely to be in an icing condition and when the evaporator is to be in a non-icing condition, characterized in that refrigerant flow control means for reducing the level of refrigerant flow in the system when an icing condition is determined and for resetting the refrigerant flow to the normal operate level when an non icing condition is determined, and means for controlling the time response by which the refrigerant flow control means reacts to the determination of at least one of the icing and non-icing conditions, in which the deterrruning means is a sensor located adjacent to the evaporator so as to determine whether the evaporator is in an icing condition or in a non-icing condition.

2. A control system as claimed in claim 1 wherein the sensor is a refrigerant pressure sensor mounted to sense pressure adjacent the output of the evaporator.

3. A contiol system as claimed in claim 1 wherein the sensor is a temperature sensor mounted to sense the evaporator temperature.

4. A control system as claimed in claim 1 wherein the refrigerant control means is a compressor clutch in which a clutch is actuated by the determining means.

5. A control system as claimed in claim 4 wherein the contiolling means includes a delay means wherein at least one of the response time of disengagement and the subsequent engagement of the clutch is delayed.

6. A contiol system as claimed in any one of claims 1 to 5 wherein the refrigerant control means includes a computer connected to monitor the determinations of the sensor.

7. A control system as claimed in claim 6 wherein the refrigerant control means is a compressor clutch in which the clutch is disengaged and engaged by the computer.

8. A mobile air conditioning system including an electrical clutch driven compressor for activation by an air conditioning system control system, a condenser, a refrigerant flow controller and an evaporator, and evaporator de-icing control system comprising: an evaporator sensor for providing an icing indication when the evaporator is in a non- icing condition, circuit means connecting the sensor to the air conditioning system control system for enabling the clutch to be activated in response to the non-icing indication and for deactivating the clutch in response to an icing indication, and means included in the circuit means for contiolling of at least one of the response times of the deactivation of the clutch in response to an icing indication and the reactivation of the clutch upon receipt of an non-icing indication.

9. A control system as claimed in claim 8 wherein the evaporator sensor is a refrigerant pressure sensor connected to the air conditioning system adjacent to the output of the evaporator.

10. A control system as claimed in claim 8 wherein the evaporator sensor is a temperature sensor located to sense the temperature of the evaporator.

11. A mobile air conditioning system including a compressor controlled by an air conditioning system contiol system including a computer, a condenser, an evaporator and a refrigerant flow controller, an evaporator icing contiol system comprising at least one sensor for monitoring the operation of the evaporator to provide one signal when a determination is made that the evaporator is likely in an icing condition and another signal when a determination is made that the evaporator is in a non-icing condition, and circuit means for connecting the sensor to the computer for the receiving signals from the sensor so that the computer reduces the flow capacity of the compressor when the icing condition is determined and resets the flow capacity of the compressor to normal operation when the non-icing condition is determined and introducing a delay in the response of the computer to at least one of the signals so that the frequency of cycling the compressor between reduced capacity and normal capacity is controlled with preset cycle limits determined by the duration of the delay.

12. A method of contiolling evaporator icing in a mobile air conditioning system including an evaporator, a condenser and a compressor comprising determining the likelihood of the presence of an icing condition in the evaporator, reducing the refrigerant flow in the air conditioning system in response to a determination of an likelihood of the presence of an icing condition in the evaporator, determining the presence of a non- icing condition in the evaporator, characterized by resetting the refrigerant flow in the air conditioning system in response to a determination of a non-icing condition in the evaporator, and delaying one of the steps of reducing the refrigerant flow and resetting the refrigerant flow in response to the determination of the presence of an icing condition and non-icing condition, respectively. 5

13. A method as claimed in claim 12, characterized by contiolling evaporator icing in a mobile air conditioning system in which the delaying step delays the reducing step, and preferably the delaying step delays the resetting step.

14. A method a claimed in claim 12 characterized by the determination of the Hkelihood of the presence of an icing condition and of a non-icing condition is made by sensing the

10 refrigerant pressure adjacent the output of the evaporator, and also preferably the determination of the likelihood of the presence of an icing condition and of a non-icing condition is made by sensing the refrigerant temperature at the output of the evaporator.

15. A method as claimed in claim 14, characterized by the reducing step includes the 15 deactivation of the compressor, and the resetting step includes the reactivation of the compressor.

16. A method as claimed in claim 15 including the step of monitoring the rate at which the compressor is deactivated and activated, and inhibiting the rate at which the compressor is deactivated and activated.

20 17. A control system as claimed in claim 16 wherein the flow controller is a temperature responsive contiol valve including a movable valve for controlling refrigerant flow, a detection circuit is coupled to the valve for detecting the movements of the valve and providing movement signals that are a function of the amount of movement, and the compressor control circuit is coupled to receive the movement signals to as to delay it

25 response to the on and off signals for movement signals corresponding to movements valve beyond a set limit.

18. A method for improving the performance of a vehicular air conditioning system including a compressor, a condenser, a refrigerant flow control mechanism, an evaporator, a compressor clutch in which the clutch has a designated limit on the rate at which the clutch is to be cycled, a contiol system for contiolling refrigerant flow in the air conditioning system by actuating and de-actuating the clutch to turn the compressor on and off respectively, and an evaporator icing detector arrangement for providing an icing signal when a determination is made that the evaporator is likely to be in an icing condition and a non-icing signal when a preset determination is made that the evaporator is not likely to be in an icing condition in which the size of differential between icing and non-icing conditions is controlled by the selection of the non-icing determination, and the sensor interacts with the contiol system to enable the control system to de-actuate the clutch in response to icing signals and to enable the contiol system to re-actuate the clutch in response to non-icing signals, characterized by delaying the control system response to at least one of the icing and non-icing signals to de-actuate or re-actuate the clutch, and setting the non-icing determination at a level so that the delay introduced in the contiol system controls the maximum rate at which the clutch can be cycled between actuation and de-actuation in response to the icing and non-icing signals.

19. A vehicular air conditioning system including a compressor, a condenser, a refrigerant flow contiol mechanism, an evaporator, a compressor clutch having a designated limit on the rate at which the clutch is to be cycled between actuated and de-actuated conditions, a control system for contiolling system refrigerant flow by actuating the clutch to enable the compressor to pump refrigerant and to de-activate the clutch to disable the compressor from pumping refrigerant, and an evaporator deicing arrangement for providing an icing signal when a determination is made that the evaporator is likely in an icing condition and a non-icing signal when a preset determination is made that the evaporator is in a non-icing condition wherein the size of differential between icing and non-icing conditions determinations is controlled by the selected non-icing determination, and the sensor arrangement interacts with the control system to enable the control system to de-actuate the clutch in response to non- icing signals, the improvement comprising means responsive to the receipt of at least on of the icing and non icing signals from the sensor arrangement for introducing a delay by which the contiol system can respond to deactivate or subsequently re-activate the clutch in response to the at least on of the icing and non icing signals to thereby allow the non icing determination be set in a direction for a reduction in the differential between icing and non-icing determinations for air conditioning system performance, while controlling the rate at which the clutch can be actuated and re-actuated by the icing and non icing signals by the delayed response of the control system.

20. A method of contiolling the refrigerant flow in a mobile air conditioning system including an evaporator, a condenser and a compressor, so as to reduce the effect of evaporator icing characterized by determining whether the evaporator is likely to be in an icing condition; reducing the refrigerant flow in response to a deterrnination that the evaporator is likely to be in an icing condition, increasing the refrigerant flow in response to a subsequent determination that the evaporator is not likely to be in an icing condition, and delaying at least one of the reducing and increasing steps, in which the reducing step reduced the pumping capacity of the compressor, and the increasing step increases the pumping capacity of the compressor.

21. A method of contiolling the refrigerant flow in mobile air conditioning system as characterized in claim 20 characterized by determining whether the evaporator is likely to be in an icing condition, reducing the refrigerant flow in response to a determination that the evaporator is likely to be in an icing condition, increasing the refrigerant flow in response to a subsequent determination that the evaporator is not likely to be in an icing condition, monitoring the motion of the control valve, and inhibiting at least on of the reducing and increasing step while a level of contiol motion is determined.

22. A method as claimed in claim 21 characterized by the step of determining if the motion of the control valve is interacting with at least one of the reducing and increasing step, and in the inhibiting step functions when a interaction is determined.

23. A method as claimed in claim 22 characterized by the step of delaying at least one of the reducing and increasing steps other than due to the monitoring step.

24. A method as claimed in claim 20 characterized by deterrnining whether the evaporator is likely to be in an icing condition, deactivating the compressor to reduce the refrigerant flow in response to a determination that the evaporator is likely to be in an icing condition, reactivating the compressor to increase the refrigerant flow in response to a subsequent determination that the evaporator is not likely to be in an icing condition , monitoring the rate at which the compressor is activated and deactivated, delaying at least one of the deactivation and reactivation steps as a function of the monitored rate, and delaying at least one of the reducing and increasing steps respectively other than due to the monitored rate.