Title of Invention

COMPRESSOR CYCLE CONTROL METHOD FOR A VEHICLE AIR CONDITIONING SYSTEM

Abstract

A control metliodology lor dynamically adjusting the switching limits of a cycled relxigerant compressor in an air conditioning system witli the objective of achieving an optimal or specified tradeoff between conipressur cycling frequency and discharge air temperature variation under all operating conditions. In a first embodiment, the compressor cycling limits are controlled to maintain a virtually constant discharge air temperature variation for all operating conditions. In a second embodiment, the compressor cycling limits are controlled so that the discharge air temperature variation changes in relation to the discharge air temperature to provide a virtually constant human comfort level for the occupants. And in a third embodiment, tlie compressoi- cycling limits are controlled so that the discharge air temperatuie variation changes in relation to the ambient or outside air temperature to provide a virtually constant human comfort level for the occupants.

Full Text

COMPRESSOR CYCLE CONTROL ME I IiOD FOR A VEHICLE AIR CONDi riONINCi SYSTEM TECHNICAL FIELD lOOOlJ The present iiiveiUion relates to a motor vehicle air conclitioiiing system including a refrigerant compressor that is cycled on and ol'f to control cooling capacity, and more particularly to a compressor cycling control method that dynamically optimizes occupant comlort and compressor reliability. BACKGROUND OF THE INVENTION [00021 The cooling capacity of an air contlilioning system including a fixed displacement refrigerant compressor is typically regiilateil by cycling the compressor on and olT. In (he exemplary automolivc air conditioning system 10 of FIG. 1, the comjiressor 12 is coupled to a driven pulley hi by an cleclrically activated clulch 16 so that compressor l .l ciin be cyclcd on and off by respectively engaging and disengaging clulch l(). I he lefrigenmt flows through a closed circuit including a condenser IK, an orllii e tube .'(I, an evaporatoi'22, and an accunuilator/dehydniloi .'I niimi(ii'il in nulcr beiwi'i'n (he compressor discharge anil suction ports Ih luid ,.!K I he cooling fans HI arc electrically activated (o provide supplenienlal aiiflow lor removing heal from high-pressure refrigerant in condenser 18, and the orifice tube 20 allows the cooled high-pressure refrigerant in line 30 lo expand in isenlhalpic i'ashion before passing through the evaporator 22. The evaporator 22 is formed as an array of finned refrigerant-conducting tubes, and an nir inlake duct 32 disposed upstream of evaporator 22 houses a motor driven ventilation blower 34 for forcing air past the evaporator tubes. The duct 32 is divided upstream of the blower 34, and an inlet air control door 36 is adjustable as shown to apportion the inlet air between outside air and cabin air, An air outlet duct 38 downstream of evaporator 22 houses a heater coi e 40 formed as an ari ay of finned tubes through which flows engine coolant. The heater core 40 effectively bifurcates the outlet duct 38, and a re-heat air control door 42 next to heater core 40 is adjustable as shown to apportion the airflow through and iiioiind heater core 40. The heated and un-heated air portions are mixed in a plenum 44 downstream of heater core 40, and Iwo discharge aii- control doors 46 and 48 are adjustable as shown to direct Ihe mixed air through one or more outlets, including a defrost outlet 50, a heater outlet 52, and driver anti passenger panel outlets 54 and 56. Activation of compressor clutch 16, cooling fans 30, blower 34, and air control doors 36, 42, 46 and 48 is controlled by a microprocessor-based controller 58. 10003] Traditionally, the controller 58 is programmed to cycle the compressor on and off as required to prevent condensate from freezing on Ihe evaporator 22, and a portion of the conditioned air is re-heated by healer core 40 so that the temperature of air discharged through (he outlets 50-56 corresponds to a desired discharge air temperature. The compiessor cycle control can be achieved with a pressure transducer responsive to the low side lefrigerant pressure, or with a temperature transducer 60 lesponsive to the evaporator outlet air temperature (Tevp). In either case, the compressor clutch 16 is disengaged when the measured paramctci' falls below a calibrated lower threshold, and is later re-engaged when the measured |iarameter rises above a calibrated upper threshold. For example, the upper and lower thresholds may be calibrated so that Tevp cycles between 3°C and 4.5°C, establishing a hysteresis band of 1.5°C. [0004] More recently, it has been proposed to improve the system efficiency by varying the compressor capacity control based on user cooling rec|uirements. In this way, the coinpres.sor cajiacily can be reduced to satisfy Ihe occupant cooling requirements with a somewhal elevated evaporator outlet iiir lemperature (or refrigerant pressure), thereby reducing both over- (leluimidification of the tlischarge air and series re-healing of the evaporator outlet air. See, for example, the U.S. Patent No. 6,2')3,l 16 to l^'orresl el al., assigned to the assignee of the present invention, and Incorporiiled by reference herein. The general principle is lo cool Ihe InliM air only as low as iieeiled to meet Ihe dischurge air lemperatuie ii'(|iiliemnil, Foi exiiniple, II Ihe discharge air lemperature larget is 10"C, Iheie IN no lU'i'il lo cool Ihe iili down lo .?"C, only lo reheal it lo IO"C. To provide al leiisl ii i erlain levi'l of dehumidification for occupant comfort and prevention of windshield fogging. Ilie evaporator temperature set point can be kepi below a limit value such as 10°C. But in general, reducing over-dehumiclification improves occupant comfort, and operating the compressor at a reducetl cajiacily improves ihe energy efficiency of the air conditioning system. This control can be achieved with an electronically controlled variable displacemeni compressor, bul it is generally more cost effective to use a fixed displacemeni compressor (hat is cycled on and off to control cooling capacity. Another possibility is to cycle a pneumatically controlled variable displacement compressor, as disclosed by Zima et al. in the U.S. Patent Application Serial No. 11/805,469, filed May 22, 2007, assigned to the assignee of the present invention, and incoi porated by reference herein. 10005] In systems where the compressor capacity is controlled by cycling, the calibrator establishes a hysteresis band defined by upper and lower switching thresholds as mentioned above. In Ihe case ol' Ihe traditional free/.e- point control, the set point (i.e., the lower threshold) is fixed at 3°C, for example, whereas in the case of the high-efficiency control, the set point varies between, say, 3°C and 10°C. In either case, the difference between Ihe upper and lower thresholds (i.e., the hysteresis band) is selected to strike a balance between the compressor clutch cycling frequency (which increases as the difference in thresholds is reduced) and discharge air temperature variation (which increases as the difference in thresholds is enlarged). In general, the calibrator .seeks to limit the compressor clutch cycling frequency to address compressor and clutch durability considerations, while limiting Ihe discharge air temperature variation to address occupant comfort considerations. This is graphically illustrated in FIGS. 2A-2B. FIG. 2A illuslralcs a freeze point control in which the compressor is cycled on and off using a fixed temperature set point 60 of 3°C following,an initial cool-down period. The set point of 3°C serves as a lower threshold, and the upper threshold 62 is calibrated to 4.5°C for a hysteresis band of 1.5°C. FIG. 2B illustrates a high efficiency control in which the compressor is cycled on and off about a variable temperature set point 64 following the initial cool-down period, in the illustration, the set point 64 has an initial value of 3°C, and then transitions to an cicvalcd value of aboul H.()°C. Similar to 1. 2A, Ihc set iioinl 64 serves as a lower Ihresholcl, and an upper Ihresholtl (>(> iracks llie set point (kI lo (lei'ine a hysteresis hand of 1Thus, the width or si/e ol'the hysteresis hand can be the same lor hiith control strategies. |(>006| A problem laced in the calibration of conipri'ssor switchinn Innits (i.e., the hysteresis band) is that the settings which provide an adeqnalc inideolT bclwecn compressor cycling frequency and disi lunge iiir lemperiiture variation under one set ol operating conditions can lull lo piovlile an adei|ni\ie liiideoff under a different set of operating condlllons Ai (iirdingly, what is needed is a way of achieving an optimal or N|iecilied tmdeoff hclween compressor cycling frequency and discharge air temperature variation under any set of operating conditions. SUMMARY OF THE INVENTION [7] The present invention is directed lo an improved control methodology for dynamically adjusting the switching limits of a cycled refrigerant compressor in an air conditioning system with the objective of achieving an optimal or specified tradeoff between compressor cycling frequency and discharge air temperature variation under all operating conditions. In a first embodiment, the compressor cycling limits are controlled to maintain a virtually constant discharge air temperature variation for all operating conditions. In a .second embodiment, the compressor cycling limits are controlled so that the discharge temperature vui iation changes in relation to the discharge air temperature to provide a virtually constant human comfort level for the occupants. And in a third embodinient, the compressor cycling limits are controlled so that the discharge air temperature variation changes in relation to the ambient or outside air temperature to provide a virtually constant human comfort level for the occupants. BRIEF DESCRIPTION OF THE DRAWINGS [8] FIG, ] is a diagram of an exemplary automotive air conditioning system, including a cycled refrigerant compressor and a microprocessor-based controller. |()0()9| FIG. 2A is a graph illustrating a traditional comprcssoi cycic control for preventing evaporator condensate IVcezing. lOOJOJ FIG. 2B is a graph iliii.strating a higii elTiciency compressor cycle control for allowing air conditioning operation at an elevated evaporator temperature. |()0111 FIG. 3A is graph depicting evaporator outlet and discharge air temperatures as a function of time with minimum re-heating ol the conditioned air. [00121 FIG. 3B is graph depicting evaporator outlet and discharge air temperatures as a function of time with maximum re-healing of the conditioned air. |00I3| FIG. 4 is a graph depicting a required variation of the evaporator outlet air tempeiature for achieving a constanl discharge air tem|ierature variation according to a first embodiment of this invention. |0(M4| FIG. 5A is a graph depicting a desired v.'iriiition of Ihe discharge iiir temperature according to second embodiment of this invention. |0015| FIG. 5B is a graph depicting a required viiriiition ol the evajioralor outlet air temperature for achieving the desired discharge iiir temperature vin iiilion de|)ic(cd in FIG. ."5 A. |00I6| FIG. 6A is a gniph depicting a desired viii iiiliiiu ot llie d|,seluu|u' ail temperature according lo third embodiment ol IIiIn liivcnlioii. 100171 FIG. 6B is a graph depicting a re(|iiired vuriiition ol tin- evaporator outlet air temperatuie foi achieving the desiiecl discliaige air ti'mpcralurc variation depicted in FIG. 6A. [18] FIG. 7 is a flow diagram of a software routine carried out by Ihe controller of FIG. 1 for cycling the compressor to achieve a desired discharge air temperature variation according to this invention. DESCRIPTION OF THE PREFERRED EMBODIMEN T [19] In general, the present invention recognizes that re-lieating conditioned air not only increases the discharge air temperature, but also lends to reduce the temperature variation of the discharge air as compared with the air at the outlet of the evaporator. This is because the heater core 40 tends to dilute or dampen temperalure variations in tlie air passing Ihroiigli it. Consequently, tiie iniluence of the heater core 40 on diseliarge air temperature variation changes depending on what portion ol' the conditioned air is directed through the heater core 40. This piienomenon is graphically ilhislralcd in FIGS. 3A-3B, which depict the evaporator outlet air teniperatuie Tevp and tiic diseliarge air temperature Tihs as a function of time for different opei-ating conditions of the air conditioning system 10. FIG. 3A depicts the temperatures Tevp and T^js when the system 10 is operating with minimal re¬heating of the conditioned air. As shown, the temperalure variation STovp of air at the outlet of evaporator 22 is virtually identical lo the temperature variation STdis of air discharged into the passenger compartment. I'lG. 3B depicts the temperatures T^.v,, and Tjis when the system 10 is operating with maximum re-heating of the conditioned air. In this ca.se, the elevated discharge air temperature T^iis exhibits a variation that is significantly reduced compared with the evaporator outlet air temperature variation 81\.v|, due lo the reduced temperature variation of the air passing through heater core 40. I0020I The influence of re-heating on the discharge air temperature variation 5T,iis makes it difficult if not impossible to calibrate the compressor cycling limits (i.e., the switching hysteresis band) in a way thai keeps ST.us within an acceptable range while also minimizing the compressor cycling fretjuency for optimal compressor and clutch durability. However, the present invention provides a way of achieving that objective through a dynamic control of the comjiressor cycling limits. According lo a first embodiment, described below in reference lo I'lO. 4, Ihe compressor cycling limits are controlled to maintain a virtually constant discharge air temperalure variation for all operating conditions. Aecoriling lo a .second embodinteni, described below in reference to FIGS. 5A-5H, the compn'ssor cycling limils aie controlled so lhat the discharge air tcmperalinv viiriiilion changes in relation to the discharge air temperature to provide a vlriually constant human coml'orl level for the nceiipanls. And accortlhin In a ihltd emliodluK'nl, described below in reference to FIGS. 6A-()II, Ihe cnmpiessot l yi ling llmlls lire controlled so tliat the discharge air temperature variation changes in relation to the ambient or oulside air temperature to provide a virtually constant human comfort level for the occupants. Finally, I'lG. 7 depicts a How diagram for carrying out the various control melhods. As described below in leference to FIG. 7, each of the above-mentioned embodiments entails determining the allowed variation in Tdis and the required varialion of the evaporator cooling capacity for achieving the allowed variation in T,iiv In general, the required variation of the evaporator cooling capacity is based on the position of the re-heat air control door 42, and the cycling thresholds i'or the compressor 12 are determined based on the required variation in evaporator cooling capacity and the desired set point for the cooling capacity of evaporator 22. In the following description, the evaporator cooling capacity, the cooling capacity set point and the compressor cycling thresholds are all expressed in terms of evaporator outlet temperature; however, it should be recognized that such parameters could alternalively be expressed in terms of low side refrigerant pressure. [0021] The discharge air temperature Tdis can be mathematically modeled as a function of various known or knowable jiarameters including the temperature Tcu of the engine coolant supplied to heater core 40, the heating effectiveness e of the heater core 40, the evaporator outlet air temperature Tevp, and the position o) of the re-hcat air control door 42 as follows: (I) where f(m) designates the fractional flow of inlet air passing through heater core 40. The heating effectiveness e, in turn, may be calculated according lo: 7' - T ^ (2) 7' -T ' rll I'lyi where T|,|| is air leinpcraliirc at tlie outlcl of licalcr corc 40. DilTcrciilialing i.'(|iialiiin (1) 1(1 provide an expression for tiie varialioii or lale oC leiiiperadire rliaii^?,e ft'I'.ns of Ihe air discharj^^ed into liie passeii^ei' eoiiipartiiieiil, yields: 100221 When I tVAC! syslern 10 is operating wilh niininial le healing of Ihe eondilioned aii' (i.e., wilh .the re-heat air eonlrol dooi '1,'. in liie "lull eold" |iosilion), the fractional flow ("((o) through lnNilert nir III K suliHlinillnlly yvm, and nl'tiis--8T,..v|, as also ilhistraled in FIG. .WV On Ihe olher hand, whiM\ aii conditioning system 10 is operating with maxiniuin le healing of die conditioned air (i.e., wiili (he re-heat airconti'ol door [00231 The first embodiment of this invention ulili/.es the above relationships to dynamically control the compressor cycling limits so (hat the discharge air temperature variation STdis is substantially constant for all operating conditions of air conditioning system 10. This is achieved by solving equation (3) for ST^.^p as follows: .yr = ^Lui— (5) in this case, the desired discharge air temperature variation 5'1'iiis is specified as a constant that is consistent with occupant comfort, and the required evaporator outlet air temperature variation 5Tevp is given as a function of the heating effectiveness e, and the heater fractional flow f(oj). The calculated term STcvp represents the switching hysteresis band required to achieve the specified discharge air temperature variation ftTdis, and the upper and lower conipressor cycling limits arc determined accortlingly. Since tiie iieating effecliveness e is subslaniialiy constant for stcady-slale operation, llie required value of can be pre-calculated as a function of re-heal air control door position 01, resulting in the control schedule dejiicled in I'Ki. 4. Hie required is equal to ST^hs when the re-heat air control dooi' 42 is in the "full cold" or 0% position as mentioned above, and increases non-linearly lo a maximum value when re-heat air control door 42 is in the "full hot" or 100% position. Whenever 8Tevp is above 8T,iis due to re-heating of conditioned air, the compressor switching hysteresis correspondingly increases to provide improved compressor and clutch durability. 100241 The second embodiment of this invention is like the first except that the compressor cycling limits are dynamically controlled to vary the discharge air temperature variation 5T(iis as a function of (he discharge air lemperatiire 'I'dis as illustrated in Figure 5A. 'I'he illuslraled air discharge leniiK'ialure variation schedule is based on human Ihernial comfort sensilivily studies which show tlial vehicle occupants arc exiremcly scnsilive lo clischiuge (lir kMuperature variations when Tdis is aboul 20"(" lo ^.'S'^C, bul less sensitive when 'r,ii,, is significanlly higher or lower than 2()"(' lo - loi convenience, a single lemperature of 25°C is used in lliis ilescri|)lioii, As ii le.Hiill, controlling iTr.n,,, us illiislrated in I'lCi. "SA can miiluliiin ii 'iulinlanlially con.slani level of human comfort under any opi'i (illii|^ i iiinlllion ol iili condilicming system 10. 100251 In a control according to the second emboiliment, the rec|uired value of 6Tev|, is again determined according lo equation {fi), excepi that the parameter 5T(iis is now a function of Tdis instead of a constant value. And the required value of 5Tevp can be pre-calculated as a function of T,iis and re-heat air control door position (o. In this regard, the graph of FIG. 5B depicts the required value of STevp as a function of door position (o for three different discharge air temperatures. The lower trace depicts the required 8T,.vp foi' T,iis = 25°C, the condition for which the discharge air temperature varialion 8 Fns is minimized. The upper trace depicts the required 8Tevp ill (he T^is extremes of 2°C or 60°C. Of course, the required STevp for discharge air temperatures between 25°C and the extreme temperatures of 2°C and 60°C are given by (races lying between the ilhistrated upper and lower traces. Significantly, this embodiment allows greater compressor switching hysleresis for improved compressor and clutch durability over an extended range of operating conditions - specifically, whenever the desired discharge air tcniperaliirc is significantly higher or lower than 25°C. 10026] In the third embodiment of this invention, the desired discharge air temperature variation 6T |0028j The How diagram of FIG. 7 reprcsciils a software routine executed by controller 58 of air conditioning system 10 for carrying out tlie above- described control metlioils. The routine is periodically executed by contioller .'iH so that; the compressor cycling limits arc dynamically adjuslcti as the operating conditions of air conditioning system 10 change over time, The illustrated routine is configured lo perform any of the first, seconti or third control strategies de,scribed above, but it will be iipprecialed tliat the routine can be simplified to perform just one olThe contiol sdiilegies il desired, |(>02| Referring lo I'lG, 7, the blocks 70 7() are liisi executed to determine a siftlable set point for the evaporaloi nullel im lemperiilKie Ah diiSeuKscd above, the set point for Tevp may ln' eaiibiiili d oi deUMiuined leased 01) different and sometimes confliclinfi, ( oiiHldeuillons, inrhiiliiig evaporator freeze protection (block 70), system energy ellicieiiey (block /.'), and windshield fog prevention (block 74). The block 76 selects the most appropriate set point ba.sed on an established priority, I'or example, if tiie set point for preventing windshield fogging is lower than the set point for optimal energy efficiency, controller 58 can be programmed to .select the .set point for preventing windshield fogging, [30] Once the set point for Tevp is established, blocks 78, 80 and 82 are executed to obtain a target value of the discharge air temperature Tjis, the re¬heat air control door position co, and the ambient temperature T,,,,,!,. if the system 10 is an automatic climate control system where the driver establishes a set temperature for the cabin and the controller 58 regulates the blower speed and air control door positions to satisfy the driver's set temperature, the target value of Tciis, co, and Tu,,,!, may be obtained from automatic climate control algorithm. If the system 10 is a so-called manual system, the target value of Tiiis is the setting of a temperature control knob or slider, and (d and Tmni, can be obtained with suitable position and temperature transducers, [31] Blocks 84-90 are then executed to determine a desired value of the discharge air temperature variation STdis using the first, second or third embodiments described above. Block 84 sets the desired value of 8T,iis to a predetermined constant as explained above in reference to the first embodiment; block 86 determines the desired value orcTI'dis based on ihe target discharge air temperature Tdis as explained above in reference (o (he second embodiment; and block 88 determines (he desired value ofiS'l'dis based on the ambient air temperature T;,,,,!, as explained above in rererencc to the third embodiment. In blocks 86 and 88, the desired value of ftT.ii.s may be determined either by table look-up or analytical runclion. Block 90 selects one of the 8T(iis values based on a calibration bit, or an established priority if desired. |0032| Once the desired value ofSTdis is determined, block 92 determines (he required value of 8Tovp based on the desired value of cVr,iis and (he re-heat air con(rol door position co. As indicated above, iSTevp can be determined by solving equation (5) directly, or by table look-up. The value of the heating effectiveness e can be predicted, or calculated if sufficien( information is available. Finally, block 94 is executed to iletermine Ihe upper and lower temperature thresholds for compressor cycling based on the set point provided by iilock 76 and the 8'l\,v|, value provided by block 92. As described above, the lowei threshold can be the set point, and the iippei threshold t iin be (he sum of Ihe se( poin( and (Vi',,vp. As with a conventioiuil control, (he controller 58 compares Ihe measured evaporator outlet air temperiiture to the upper and lower temperature (hresholds (o control compresNor cyclllig. |(MM3| In summary, Ihe present invention piovMen n novel mi'lhodoluny lor dyniunically controlling compressor clutcli I'vclliiti hii'ied mi nil conditioning system operating parameters (o aelilevi! iin optimiil or speellli'd (radeoff between compressor cycling frequency and discharge air temperatuie variation under any set of operating conditions. While (he presen( inven(ion has been described with respect to the illuslrated embodimen(s, i( is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the control may be based on low side refrigerant pressure instead of evaporator outlet air temperature as mentioned above, and (he specific temperatures and curve shapes shown herein are exemplary in nature, and may vary somewhat depending on the application. Accordingly, it is intended that Ihe invention not be limited to the disclosed embodiment, but that it have the fuli scope permitted by the language of the following claims. DP-3I738I - NiiiiilH'ird Cl;iinis & Alislriicl loi l'i)rci}j,ii I'lliiij; CLAIMS 1. A method of operation for an air conditioning system (10) including an evaporator (22) for conditioning inlet air, a refrigerant comjiressor (12) that is cycled on and off to control a cooling capacity of the evaporator (22), and a heater core (40) configured to re-heat a selected portion of the conditioned 5 inlet air to affect a discharge air temperature of the system (10), the method comprising the steps of: determining a desired set point (70-74) for the cooling capacity of the evaporator (22); determining what portion of the conditioned air is re-heated (HO) by the 10 heater core (40); determining an allowed variation in the discharge air temperature (84- 88); determining a retiuired variation of the evaporator cooling capacity for achieving the allowed variation in the discharge air temperature (92) based on 15 allowed variation in the discharge air temperature and the determined portion of conditioned air that is re-heated by the heater core (40); and cycling the compressor (12) on and off according to the desired set point and the required variation in evaporator cooling capacity (94, 58, 1()). 2. The method of claim 1, including the steps of: determining upper and lower switching thresholds for the evaporator cooling capacity based on the desired set point and the recjuired variation in evaporator cooling capacity (94); and 5 cycling the compressor on and off by comparing a measure of the evaporator cooling capacity with the upper and lower switching thresholds (58, 16). 3. The method of claim 1, where: the desired sel point for the evaporator cooling capacity is a dcsiicd oullel air temperature of liie evaporator (22); and liie required variation of the evaporator cooling capacity is a rcciuiretl varialion in the oullel aii' lenipeiature oftlie evapoialoi (.'.'). 'I. The nieihotl ol claim I, where: Ihe allowed varialion in the discharge air lenipeniliire is a s|)ecilied I'oiislanI value (K4). 5. The melhod oT claim 1, including llu- sli'p ol; determining Ihe alloweil varialion in Ihr dlKrliai |ir nir li'inpernlnie as a liiiiclion of Ihe discharge air leniperalure (!U») 6. The method of claim 5, where: the allowed varialion in the discharge air lemiieiaUire has a minimum value at a discharge air temperature of approximulely 2()"(' lo 2.'i"C, 7. The method of claim 1, including (he steps of; determining an ambient air temperature (82); and determining the allowed variation in Ihe discharge air temperaUire as a function of (he determined ambient air temperalure (HK), 8. The melhod of claim 7, where: the allowed variation in the discharge air temperalure has a minimum value at an ambient air temperature of about 20°C to 25'C. 9. The method of claim I, including the step of: determining (92) the required variation of the evaporator cooling capacity for achieving the allowed variation in Ihe discharge air leniperalure in accordance with: where (37,//t is the allowed variation in the discharge air leniperalure, /fV*;) is ihe delermined portion of conditioned air that is re-healed by the heater core (40), and is a healing effectiveness of the healer core (40), 10. The method of claim 1, where the air coiulilioning system (10) includes an air control door (42) for controlling what portion ol condiliojied air is re-heatcd by the heater core (40), and Ihe method includes the sleps of: deterniining (80) a position of said air control iloor (42); aiul determining (5K) what portion of the conditioned air is re4iealed by the heater core (40) based on Ihe determined position of said air control door (42).

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878-CHE-2009 ABSTRACT.pdf

878-CHE-2009 AMENDED CLAIMS 11-08-2014.pdf

878-CHE-2009 CLAIMS.pdf

878-CHE-2009 CORRESPONDENCE OTHERS 06-06-2014.pdf

878-CHE-2009 CORRESPONDENCE OTHERS.pdf

878-CHE-2009 DESCRIPTION (COMPLETE).pdf

878-CHE-2009 DRAWINGS.pdf

878-CHE-2009 EXAMINATION REPORT REPLY RECEIVED 11-08-2014.pdf

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878-CHE-2009 FORM-3 11-08-2014.pdf

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878-CHE-2009 ASSIGNMENT 13-10-2009.pdf

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