now referring to fig1 the air conditioning system of the present invention includes a prime mover 10 ( such as an internal combustion engine ) coupled to air conditioning compressor 16 by way of shaft 12 , belt 14 , and clutch 15 . a / c compressor 16 is adapted to circulate refrigerant through evaporator 20 by way of fluid circuit 18 . air 22 is passed across evaporator surface 24 wherein the heat is removed from the air and transferred to the refrigerant . the refrigerant flows from the evaporator to the condenser ( condenser not shown ) where the heat contained therein is transferred to the ambient air . temperature sensing probe 26 is coupled to evaporator surface 24 wherein it converts the temperature of the evaporator surface to an electronic signal and transfers the signal to electronic body controller 28 . electronic body controller 28 determines if conditions are present for fogging to occur 30 . a desired temperature 32 is calculated , and the strategy for calculating the desired temperature , is based on , in part , the possibility ( or lack ) of the occurrence of a fogging condition 30 . electronic body controller 28 uses the strategy employed in 30 , 32 , to determine if clutch 15 should be engaged or disengaged . this determination is encoded an electric signal and passed along to electronic engine controller 36 by way of communication buss 38 . electronic engine controller 36 supplies current to air conditioning relay 40 which , in conjunction with vehicle power source 42 engages or disengages clutch 15 . the operation of the anti - fogging strategy employed within electronic body controller 28 will now be discussed . in discussing the strategy , the following variable names will be used . table a______________________________________variable name definition______________________________________evap . sub .-- temp the current evaporator temperaturedesired . sub .-- steady . sub .-- st the desired steady state tempera - ture of the evaporatordesired . sub .-- float . sub .-- st the desired floating temperature of the evaporatorinit . sub .-- temp . sub .-- cyc . sub .-- pt initial temperature cycle point constant______________________________________ now referring to fig1 and 2 , the first determination made by the anti - fogging strategy of the present invention , is to determine if conditions are present for causing fogging 44 . if there are no conditions present for causing fogging , electronic body controller 28 enters into its steady state control scheme 46 . the steady state control scheme 46 includes monitoring the temperature of evaporator 20 , engaging a / c clutch 15 when the evaporator temperature exceeds the desired steady state temperature by more than 1 ° f . 48 , and disengaging a / c clutch 15 when the evaporator temperature is less than 1 ° f . below the desired steady state temperature 50 . if the evaporator temperature is not above or below the desire steady state temperature by more than 1 ° f ., clutch 15 is left in its present state 52 . steady state control strategy 46 is graphically represented in fig3 wherein the desired steady state temperature 54 is set at a predetermined temperature level . in determining whether fogging conditions exist 44 , two conditions are checked . firstly , if the engine ( or prime mover ) has just been started , conditions can be present which cause fogging . secondly , if clutch 15 has been disengaged for a period of time which exceeds a predetermined fixed period , then conditions can occur which cause fogging . if either of the above two conditions are present , conditions are present for causing fogging and the logic flow proceeds to step 56 . the current evaporator temperature is read and the initial temperature cycle point constant is retrieved . the initial temperature cycle point constant is a fixed temperature value that represents the coldest temperature to which the evaporator can be lowered without cycling the compression clutch and without causing fogging . it is contemplated that the initial temperature cycle point value is determined by subjecting the vehicle to a high humidity condition and then lowering ( in one step ) the temperature of the evaporator from the ambient temperature to a predetermined temperature . if no fogging occurs , a lower temperature is selected and the test is run again . at some point in conducting such a test , fogging will occur and the evaporator temperature which causes fogging defines the limit for the initial temperature cycle point temperature constant . preferably , such a test is conducted for each a / c system design contemplated because the design of an a / c system has some influence on the value of the initial temperature cycle point constant . a fixed offset ( such as 2 ° f .) is subtracted from the evaporator temperature and this value is compared against the initial temperature cycle point constant . the desired floating state variable is set equal to the lesser of these two values 58 . a / c clutch 15 is engaged 60 and the floating state control strategy 62 commences . with the a / c clutch engaged coolant flows through evaporator 20 and begins to lower its temperature . as soon as the evaporator temperature is one degree less than the desired floating state temperature 64 a command is issued 66 to disengage a / c clutch 15 . upon disengagement of a / c clutch 15 the evaporator temperature will begin to rise as circulating air 22 is passed over evaporator surface 24 . as soon as the evaporator temperature is warmed to a temperature which is one degree greater than the desired floating state temperature 68 , the desired floating state temperature is decremented by predetermined amount 70 ( such as 2 ° f .) and a check is made to determine if the desired floating state temperature is equal to or less than the desired steady state temperature 72 . if this occurs , the temperature of the evaporator has been decremented a sufficient number of times so that it now has reached the desired steady state temperature and the steady state control strategy 46 can now be used 74 . if the desired floating state temperature is still greater than the desired steady state temperature than the floating state control strategy 62 is executed once again 76 . the floating state control 62 of the present invention is graphically illustrated in fig4 and 5 . fig4 shows evaporator temperature 78 having an initial value 80 and dropping therefrom as soon as refrigerant begins to flow through evaporator 20 . desired floating state temperature 82 is selected as the lesser of the initial temperature cycle point constant or two degrees less than the evaporator temperature . in most cases , the initial temperature cycle point constant will be much less than two degrees lower than the evaporator temperature and accordingly , the initial temperature cycle point constant will be the desired floating state temperature value . the use of an initial temperature cycle point value is critical to the quick initial responsiveness of the anti - fogging system of the present invention . because the initial temperature cycle point value will , under normal conditions , be much less than two degrees less than the evaporator temperature , it allows the evaporator to initially cool at a much quicker rate than it could otherwise do if the strategy simply initiated cooling by decrementing the evaporator temperature two degrees at a time . of course , the initial temperature cycle point constant must be carefully chosen ( as disclosed in the scheme previously discussed ) so that evaporator 20 does not initially cool too quickly . if evaporator 20 is allowed to cool too quickly , fogging occurs and thus the purpose of the anti - fogging strategy is defeated . fig4 generally depicts a control led decline of evaporator temperature 78 until the temperature of evaporator 78 is coincident with the desired steady state temperature 54 . now referring to fig5 an enlarged view of a portion of fig4 shows that clutch 15 is engaged until evaporator temperature 78 drops below desired floating state temperature 82 by approximately 1 ° f . 84 . when this occurs , clutch 15 is disengaged and the evaporator temperature 78 begins to rise by virtue of warm air 22 passing over evaporator 20 . the temperature 78 is allowed to rise until it exceeds desired floating state temperature by approximately one degree 86 . next , a / c clutch 15 is engaged 88 and desired floating state temperature 82 is decremented by predetermined amount 90 ( preferably 2 ° f .). evaporator temperature 78 begins to fall until it drops one degree below the newly adjusted desired floating state temperature 92 . this cycle continues until desired floating state temperature 82 is coincident with desired steady state temperature 54 as has already been explained in conjunction with fig4 . by allowing evaporator temperature 78 to drop one degree below desired floating state temperature 82 and then allowing it to rise one degree above desired floating state temperature 82 , local cold spots in the surface 24 of evaporator 20 dissipate . thus , this cycling strategy forms an effective means for ensuring that the temperature of evaporator surface 24 is uniform . thus , fogging is minimized or eliminated . the foregoing detailed description shows that the preferred embodiments of the present invention are well suited for fulfill the objects of the invention . it is recognized that those skilled in the art may make various modifications or additions to the preferred embodiments chosen here to illustrate the present invention without departing from the spirit of the present invention . for example , fixed temperature decrements and increments of 1 ° f . and 2 ° f . have been discussed in conjunction with the anti - fogging strategy of the present invention . however , it is contemplated that other fixed temperature differentials of various magnitudes may be used without deviating from the teaching of the disclosed strategy . accordingly , it is to be understood that the subject matter sought to be afforded protection thereby should be deemed to extend to the subject matter defined in the appended claims , including all fair equivalents thereof .