Patent Publication Number: US-6983793-B2

Title: Dual evaporator air conditioning system and method of use

Description:
FIELD OF THE INVENTION 
   The present invention relates to a dual evaporator air conditioning system for cooling air in a cabin of a vehicle and a method of cooling the air using the dual evaporator air conditioning system. More specifically, the present invention relates to the dual evaporator air conditioning system having primary and auxiliary HVAC units to cool the air in the front and rear portions of the cabin and the method of cooling the air in the front and rear portions of the cabin using the dual evaporator air conditioning system. 
   BACKGROUND OF THE INVENTION 
   Dual evaporator air conditioning systems are well known in the art for cooling air in front and rear portions of a cabin of a vehicle. A typical dual evaporator air conditioning system includes a primary HVAC unit to cool the front portion of the cabin and an auxiliary HVAC unit to cool the rear portion of the cabin. The primary HVAC unit includes a primary evaporator and the auxiliary HVAC unit includes an auxiliary evaporator. The primary and auxiliary evaporators are fluidly connected to a common compressor and common condenser. The compressor compresses and circulates refrigerant to the condenser. The condenser cools and condenses the refrigerant, which is then circulated to both the primary and auxiliary evaporators. 
   The primary evaporator is held by a primary housing and is used to transfer heat from the air to the refrigerant. A primary blower moves the air across the primary evaporator, and a plurality of primary air ducts direct the air into the front portion of the cabin. The auxiliary evaporator is held by an auxiliary housing and is used to transfer heat from the air to the refrigerant. An auxiliary blower moves the air across the evaporator, and a plurality of auxiliary air ducts direct the air into the rear portion of the cabin. 
   Examples of dual evaporator air conditioning systems are shown in U.S. Pat. No. 4,949,779 to Kenny et al. (the &#39;779 patent) and U.S. Pat. No. 5,142,881 to Nagayama (the &#39;881 patent). The dual evaporator air conditioning systems of the &#39;779 and the &#39;881 patents include primary and auxiliary evaporators connected to a common compressor to cool front and rear portions of a vehicle cabin. 
   Dual evaporator air conditioning systems of the prior art utilize a control system to control operation of the compressor and the primary and auxiliary HVAC units to cool the front and rear portions of the cabin. Generally, the control system activates the compressor when the primary HVAC unit is in a cooling mode, i.e., a user has requested cooled air for the front portion of the cabin. The auxiliary HVAC unit can also be in a cooling mode, i.e., the user has requested cooled air for the rear portion of the cabin. Alternatively, the auxiliary HVAC unit can remain in a non-cooling mode while the primary HVAC unit is in the cooling mode, i.e., the user has requested cooled air for the front portion, but not for the rear portion. In this instance, the compressor continues to circulate refrigerant through the auxiliary evaporator of the auxiliary HVAC unit even though the auxiliary HVAC unit is in the non-cooling mode. In such a case, liquid refrigerant and lubricating oil begin to accumulate in the auxiliary evaporator. 
   The liquid refrigerant and lubricating oil become stored or trapped in the auxiliary evaporator because the auxiliary evaporator is not transferring heat from the air in the rear portion of the cabin to the refrigerant in the auxiliary evaporator. As a result, the refrigerant is not converted to a vapor and the viscosity of the refrigerant in the auxiliary evaporator increases. As the viscosity of the refrigerant increases, more and more lubricating oil becomes trapped in the refrigerant to remain in the auxiliary evaporator. Accumulation of the liquid refrigerant and lubricating oil in the auxiliary evaporator results in refrigerant starvation to the rest of the system and poor compressor lubrication. 
   When liquid refrigerant is stored in the auxiliary evaporator, refrigerant for the rest of the dual evaporator air conditioning system is reduced. If the amount of liquid refrigerant that is stored is greater than a reserve charge, the primary evaporator will operate at a sub-critical charge. Furthermore, when lubricating oil is trapped in the auxiliary evaporator, the compressor does not receive adequate lubrication resulting in wear and tear of the compressor&#39;s internal components. Prior art dual evaporator air conditioning systems attempt to alleviate the buildup of the liquid refrigerant and lubricating oil in the auxiliary evaporator by adding a valve upstream of the auxiliary evaporator. The valve is closed when the auxiliary HVAC unit is in the non-cooling mode and open when the auxiliary HVAC unit is in the cooling mode. Such valves are relatively expensive, and require considerable attention and maintenance to ensure proper operation. As a result, there is a need in the art for an improved, economically feasible system to minimize refrigerant collection in the auxiliary evaporator. 
   SUMMARY OF THE INVENTION AND ADVANTAGES 
   The present invention provides a dual evaporator air conditioning system for use with a refrigerant for cooling air. The dual evaporator air conditioning system includes a compressor to compress and circulate the refrigerant through a primary air conditioning unit and an auxiliary air conditioning unit. The primary air conditioning unit includes a primary evaporator to transfer heat from the air to the refrigerant to cool the air. The auxiliary air conditioning unit includes an auxiliary evaporator to transfer heat from the air to the refrigerant to cool the air. A heater is near the auxiliary evaporator to heat the refrigerant and prevent accumulation of liquid refrigerant and lubricating oil in the auxiliary evaporator. 
   A method of cooling the air is also provided. The method uses the dual evaporator air conditioning system to cool the air. To start, each of the primary and auxiliary air conditioning units are switched from the non-cooling mode to the cooling mode. The compressor is then activated in response to the primary air conditioning unit being switched from the non-cooling mode to the cooling mode. Refrigerant circulates through the primary evaporator and the auxiliary evaporator in response to activating the compressor. Primary and auxiliary blowers are then activated to transfer heat from the air to the refrigerant to cool the air. The blowers are activated in response to the primary and auxiliary air conditioning units being in the cooling mode. The cooled air is discharged from the primary and auxiliary air conditioning units in response to activating the blowers. Next, the auxiliary air conditioning unit is switched from the cooling mode to the non-cooling mode while the primary air conditioning unit remains in the cooling mode. As a result, the heater near the auxiliary evaporator is automatically activated in response to the auxiliary air conditioning unit being switched from the cooling mode to the non-cooling mode while the primary air conditioning unit remains in the cooling mode. 
   The present invention provides several advantages over the prior art. In particular, the heater of the present invention is automatically activated in response to the auxiliary air conditioning unit being in the non-cooling mode while the primary air conditioning unit is in the cooling mode. As a result, the heater transfers heat to the refrigerant even though the auxiliary air conditioning unit is in the non-cooling mode. With a continuous transfer of heat from the heater, the refrigerant in the auxiliary evaporator will be converted to vapor that easily moves through the auxiliary evaporator without being trapped therein. The result is a reduction in the amount of liquid refrigerant and lubricating oil stored or trapped in the auxiliary evaporator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of a vehicle having a dual evaporator air conditioning system of the present invention; 
       FIG. 2  is a cross-sectional and partially schematic view of the dual evaporator air conditioning system of the present invention; and 
       FIG. 3  is a block diagram illustrating a control system of the dual evaporator air conditioning system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a dual evaporator air conditioning system for use with a refrigerant to cool air in front and rear portions  10 , 12  of a cabin  14  of a vehicle  16  is shown generally at  20 . The dual evaporator air conditioning system  20  is positioned in a vehicle body  22  of the vehicle  16 . The vehicle body  22  defines the front and rear portions  10 , 12  of the cabin  14  of the vehicle  16 . 
   The dual evaporator air conditioning system  20  works to cool the air in the front and rear portions  10 , 12  of the cabin  14  by circulating the refrigerant in a refrigerant cycle to absorb heat from the air. The dual evaporator air conditioning system  20  comprises a primary HVAC unit  28  and an auxiliary HVAC unit  30 , shown in cross-section in  FIG. 2 . The primary HVAC unit  28  is preferably positioned in the vehicle  16  near the front portion  10  of the cabin  14 . The primary HVAC unit  28  includes a primary evaporator  32  in the refrigerant cycle to cool the air in the front portion  10  of the cabin  14 . Referring to  FIG. 1 , the primary HVAC unit is disposed in the vehicle body  22  of the vehicle  16  near an engine compartment  24 . 
   The auxiliary HVAC unit  30  is preferably positioned in the vehicle  16  near the rear portion  12  of the cabin  14 . Referring to  FIG. 1 , the auxiliary HVAC unit  30  is disposed in a chamber  26  defined by the vehicle body  22 . The chamber  26  is separate from the front and rear portions  10 , 12  of the cabin  14 . In particular, the chamber  26  is partitioned from the rear portion  12  of the cabin  14  by interior molding  34 . Preferably, the interior molding  34  is an inner side panel in the rear portion  12  with the chamber  26  being set back and partially sealed behind the side panel. The shape of the chamber  26  is similar to the auxiliary HVAC unit  28  to reduce size requirements. The auxiliary HVAC unit  30  includes an auxiliary evaporator  36  in the refrigerant cycle to cool the air in the rear portion  12  of the cabin  14 . 
   Referring specifically to  FIGS. 1 and 2 , a compressor  38  is in fluid communication with both the primary and auxiliary evaporators  32 , 36 . The compressor  38  is disposed within the vehicle body  22  of the vehicle  16  to compress and circulate the refrigerant in the refrigerant cycle. The type of refrigerant used with the dual evaporator air conditioning system  20  of the present invention is preferably one that exhibits efficient heat transfer rates while being environmentally friendly. The refrigerant used with the dual evaporator air conditioning system  20 , however, is not intended to limit the present invention. 
   A condenser  40  is disposed within the vehicle body  22  and in the refrigerant cycle to receive the compressed refrigerant from the compressor  38 . The refrigerant entering the condenser  40  from the compressor  38  is generally in the form of a gas. The condenser  40  then cools and condenses the refrigerant. The refrigerant exits the condenser  40  as a high-pressure liquid and travels to an expansion device  42  upstream of each of the primary and auxiliary HVAC units  28 , 30 . 
   The expansion device  42  expands the refrigerant from the condenser  40  to provide the primary and auxiliary evaporators  32 , 36  with a low quality vapor. It should be appreciated by those skilled in the art, that the compressor  38  and condenser  40  are common to both units, i.e., one compressor  38  and one condenser  40  are used in the refrigerant cycle. 
   The refrigerant is circulated in primary and auxiliary parallel loops  44 , 46  of the refrigerant cycle to the primary and auxiliary evaporators  32 , 36  of the HVAC units  28 , 30 , respectively. The primary and auxiliary parallel loops  44 , 46  are interconnected such that the refrigerant from the condenser  40  moves through both of the loops  44 , 46  to the primary and auxiliary evaporators  32 , 36 . The refrigerant is converted from a low quality vapor to a high quality vapor or gas in the primary and auxiliary evaporators  32 , 36 . From the auxiliary evaporator  36 , the gas refrigerant travels back to the compressor  38  to begin the cycle again. From the primary evaporator  32 , the refrigerant travels first to an accumulator-dehydrator canister  48  to separate any liquid refrigerant from the vapor refrigerant and then back to the compressor  38  to begin the cycle again. 
   It should be appreciated that the refrigerant cycle is generally illustrated and is not intended to limit the present invention. For example, the dual evaporator air conditioning system  20  may be configured without the accumulator-dehydrator canister, but with a receiver when a thermal expansion valve is employed. 
   The primary evaporator  32  is a heat exchanger that transfers heat from the air in the front portion  10  of the cabin  14  to the refrigerant that is circulating through the primary parallel loop  44 . The primary evaporator  32  cools the air for the front portion  10  of the cabin  14 . A primary housing  50  surrounds the primary evaporator  32 . As previously described, the refrigerant enters the primary evaporator  32  as a low quality vapor and exits as a high quality vapor or gas. A primary blower  52  is disposed in the primary housing  50  and engages the primary housing  50  to move the air from the front portion  10  of the cabin  14  across the primary evaporator  32  to transfer the heat from the air to the refrigerant. This movement of air is illustrated using arrows in  FIG. 2 . 
   Alternatively, the primary blower  52  may receive air from outside the vehicle  16  that is first filtered through an intake filter  54  to be moved across the primary evaporator  32 . It will be appreciated by those skilled in the art that the intake filter  54  is not necessary to draw outside air into the primary HVAC unit  28 . Either outside air or the air from the front portion  10  of the cabin  14  can be cooled in the primary HVAC unit  28 . Referring to  FIG. 2 , an intake door  56  can be used to switch between outside air and air from within the cabin  14 . An outside air duct  58  and a return duct  60  are used to direct the air into the primary HVAC unit  28 . The intake door  56  alternates between two positions  57 , 59  to switch between drawing outside air and drawing air from the cabin  14  into the primary housing  50 . Regardless of the air source, the liquid refrigerant in the primary evaporator  32  begins to boil due to the heat in the air moving across the primary evaporator  32  (the refrigerant typically has a low boiling point). The refrigerant, therefore, changes phases, i.e., from the liquid refrigerant to the vapor refrigerant phase and absorbs heat from the air. 
   A plurality of primary air duct housings  63  extend from and engage the primary housing  50  to define a plurality of primary air ducts  62  to distribute the air from the primary HVAC unit  28  into the front portion  10  of the cabin  14 . The plurality of primary air ducts  63  is downstream of the primary evaporator  32 , i.e., the air is cooled before reaching the primary air ducts  62 . A first mode door  64  that is downstream of the primary evaporator  32  engages the primary housing  50  and is movable between first and second positions  66 , 68  to selectively distribute the air into the primary air ducts  62  to be distributed into the front portion  10  of the cabin  14 . Preferably, the first mode door  64  pivots relative to the primary housing  50  to change the positions  66 , 68 . A second mode door  70  engages the primary housing  50  and is movable between first and second positions  72 , 74  to selectively distribute the air into the primary air ducts  62  to be distributed into the front portion  10  of the cabin  14 . Preferably, the second mode door  70  pivots relative to the primary housing  50  to change the positions  72 , 74 . 
   The plurality of primary air ducts  62  include a primary defrost duct  76 , a primary vent duct  78 , and a primary floor duct  80 . The first mode door  64  is upstream of the second mode door  70  and diverts cooled air to the primary defrost duct  76  in the second position  68  and closes the primary defrost duct  76  in the first position  66 . The second mode door  70  diverts cooled air to the primary vent duct  78  in the first position  72  and to the primary floor duct  80  in the second position  74  (when the first mode door  64  is in the first position  66 ). It should be appreciated that the number of mode doors  64 , 70 , or primary air ducts  62  used to divert the cooled air from the primary HVAC unit  28  is not intended to limit the present invention. It should be appreciated by those skilled in the art, that many different configurations could be utilized. 
   The auxiliary evaporator  36  is a heat exchanger that transfers heat from the air in the rear portion  12  of the cabin  14  to the refrigerant circulating through the auxiliary parallel loop  46 . The auxiliary evaporator  36  cools the air for the rear portion  12  of the cabin  14 . An auxiliary housing  82  surrounds the auxiliary evaporator  36 . As previously described, the refrigerant enters the auxiliary evaporator  36  as a low quality vapor and exits as a high quality vapor. An auxiliary blower  84  is disposed in the auxiliary housing  82  and engages the auxiliary housing  82  to move the air from the rear portion  12  of the cabin  14  across the auxiliary evaporator  36  to transfer the heat from the air to the refrigerant. As a result, any liquid refrigerant in the auxiliary evaporator  36  begins to boil. The refrigerant, therefore, changes phases, i.e., from the liquid refrigerant to the vapor refrigerant phase thereby absorbing heat from the air. 
   An air intake vent  112 , near the auxiliary housing  82 , engages the interior molding  34  and operatively communicates with the rear portion  12  of the cabin  14 . The air intake vent  112  guides the air from the rear portion  12  into the auxiliary housing  82  upstream of the auxiliary blower  84 . An air filter  114  may be disposed between the air intake vent  112  and the auxiliary housing  82  to remove particles from the air. 
   A plurality of auxiliary air duct housings  105  extend from and engage the auxiliary housing  82  to define a plurality of auxiliary air ducts  104  to distribute the cooled air into the rear portion  12  of the cabin  14 . In the preferred embodiment, the plurality of auxiliary air ducts  104  include an auxiliary vent duct  106  and an auxiliary floor duct  108  communicating with the auxiliary housing  82  to distribute the air from the auxiliary HVAC unit  30  into the rear portion  12  of the cabin  14 . An auxiliary mode door  86  engages the auxiliary housing  82  and is movable between first and second positions  87 , 88  to direct the cooled air into the rear portion  12  of the cabin  14 . The first and second positions  87 , 88  correspond to vent and heater modes of the auxiliary HVAC unit  30 . The first position  87  corresponds to discharging the cooled air through the auxiliary vent duct  106  and the second position  88  corresponds to discharging the cooled air through the auxiliary floor duct  108 . 
   Referring to  FIGS. 2 &amp; 3 , a heater  90  is mounted to the auxiliary evaporator  36  to heat the refrigerant inside the auxiliary evaporator  36 . Alternatively, the heater  90  can be mounted to the auxiliary housing  82  adjacent to the auxiliary evaporator  36 . The heater  90  could be any number of systems capable of heating the refrigerant in the auxiliary evaporator  36  and converting the liquid refrigerant to the vapor refrigerant. For example, the heater  90  may be a heating element such as a resistance surface heater that is electrically operative to heat the auxiliary evaporator  36  and the refrigerant inside. It will be appreciated by those skilled in the art that the heater  90  could also be a type of heat exchanger using other heat sources such as engine coolant. The heater  90  may also be a heater core, oil cooler, PTC heater or any electronically, chemically, mechanically operative heaters, and the like. The heater  90  may extend across and/or cover the auxiliary evaporator  36 , or alternatively, the heater  90  may extend across only a portion of the auxiliary evaporator  36 . The heater  90  may also be mounted to a side of the auxiliary evaporator  36 , as shown by the broken lines in  FIG. 2 . 
   Preferably, the heater  90  is insulated from the air within the auxiliary HVAC unit  30  by an insulator  98 . The insulator can cover one side of the heater  90  opposite the auxiliary evaporator  36  such that the heat from the heater  90  is directed toward the auxiliary evaporator  36 . The insulator  98  may be comprised of a number of different insulating materials including, but not limited to fiberglass pulp, glass or porcelain, ceramic, ebonite, paraffin, rubber or plastic, metal wrapping, and the like. The insulator  98  and the heater  90  should be resistant to corrosion resulting from exposure to the conditions within the auxiliary HVAC unit  30 . 
   The dual evaporator air conditioning system  20  includes a control system  116  having cooling and non-cooling modes  118 , 119 , 120 , 121  for each of the HVAC units  28 , 30  to control the dual evaporator air conditioning system  20 . Preferably, the control system  116  includes a controller  124  centralized within the control system  116  to control the dual evaporator air conditioning system  20 . The controller  124  utilizes input signals and control signals, as is well known in the art, to control the dual evaporator air conditioning system  20 . It will be appreciated that the controller  124  is powered by a power source in the vehicle  16  such as a battery, power cell, power generator, or the like. A control panel (not shown) that is operatively connected to the controller  124  and accessible to a user of the vehicle  16  is used to control several features of the control system  116 . 
   Preferably, the user controls whether the primary and auxiliary HVAC units  28 , 30  are placed in the cooling mode  118 , 119  or the non-cooling mode  120 , 121 . The user selects the cooling or non-cooling mode  118 , 119 , 120 , 121  for each of the HVAC units  28 , 30  based on whether the user wishes to provide cooled air to the front and/or rear portions  10 , 12  of the cabin  14 . Preferably buttons on the control panel, schematically represented in  FIG. 3 , are used to request the cooled air for the front and rear portions  10 , 12  of the cabin  14 . Although  FIG. 3  illustrates separate buttons for the cooling and non-cooling modes  118 , 119 , 120 , 121 , it is preferable to utilize a single button for each of the primary and auxiliary HVAC units  28 , 30 . In this manner, each air conditioning unit is placed in the cooling mode  118 , 119  when the user activates the corresponding button. Conversely, each air conditioning unit is placed in the non-cooling mode  120 , 121  when the user deactivates the corresponding button. Pressing the buttons sends input signals to the controller  124  to indicate the user&#39;s desired cooling conditions. The controller  124  then uses those input signals to control other aspects of the control system  116  as will be described further below. 
   The user also controls temperature settings for the front and rear portions  10 , 12  of the cabin  14  and primary and auxiliary blower speeds to temperately control the air in the front and rear portions  10 , 12 . It should be appreciated by those skilled in the art that user control of the primary and auxiliary HVAC units  28 , 30  could be accomplished in several ways. Therefore, the specific manner in which the user controls the primary and auxiliary HVAC units  28 , 30  is not intended to limit the present invention. 
   Many features of the control system  116  are controlled automatically, i.e., control signals are automatically sent from the controller  124  in response to the input signals sent to the controller  124 . For instance, the compressor  38  is automatically activated when the user has selected the cooling mode  118  for the primary HVAC unit  28 . The compressor  38  then begins to automatically circulate refrigerant through the refrigerant cycle. 
   In the preferred embodiment, the control system  116  automatically activates the heater  90  in response to the auxiliary HVAC unit  30  being in the non-cooling mode  121  while the primary HVAC unit  28  is in the cooling mode  118 . When the user has selected the cooling mode  118  for the primary HVAC unit  28 , a control signal is sent from the controller  124  to the compressor  38  and the compressor  38  is activated. The compressor  38  then begins to circulate refrigerant through the refrigerant cycle. This includes circulating refrigerant through both the primary and auxiliary evaporators  32 , 36  even though the user has selected the non-cooling mode  121  for the auxiliary HVAC unit  30 . The primary blower  52  moves air across the primary evaporator  32  to transfer heat from the air to the refrigerant in the primary HVAC unit  28 . However, since the user has selected the non-cooling mode  121  for the auxiliary HVAC unit  30 , air is not moved across the auxiliary evaporator  36  to be cooled, i.e., the user has selected not to cool the rear portion  12  of the cabin  14 . As a result, heat from the air is not transferred to the refrigerant. Therefore, the heater  90  is automatically activated to heat the refrigerant and prevent accumulation of liquid refrigerant and lubricating oil in the auxiliary evaporator  36 , as previously described. Preferably, an electrical output signal is sent from the controller  124  to the heater  90  to activate the heater  90 . 
   A temperature sensor  94  such as a thermocouple may be positioned near the heater  90  to determine the temperature of the heater  90 . The temperature sensor  94  is operatively connected to the controller  124  to relay the temperature of the heater  90  back to the controller  124 . The controller  124  controls the temperature of the heater  90  when the auxiliary HVAC unit  30  is in the non-cooling mode  121  while the primary HVAC unit  28  is in the cooling mode by adjusting the electrical control signal sent from the controller  124  to the heater  92 . The temperature of the heater  90  varies as a magnitude of the control signal varies. The controller  124  may be programmed to adjust the temperature of the heater  90  based on a predetermined condition such as an average temperature in the auxiliary housing  82  or to maintain a steady optimum temperature for converting liquid refrigerant to vapor or gas refrigerant. 
   The control system  116  includes a sensor  128  that is operatively connected to the controller  124 . The controller  124  is responsive to the sensor  128  to sense when the auxiliary HVAC unit  30  is in the non-cooling mode  121  while the primary HVAC unit  28  is in the cooling mode  118 . Preferably, the sensor  128  represents computer code within the controller  124  that recognizes the input signals triggered by the user to determine when the auxiliary HVAC unit  30  is in the non-cooling mode  121  while the primary HVAC unit  28  is in the cooling mode  118 . 
   The control system  116  includes an auxiliary blower controller  132  that is operatively connected to the controller  124 . The auxiliary blower controller  132  actuates a motor  133  to rotate the auxiliary blower  84  when the auxiliary HVAC unit  30  is in the cooling mode  119 . The auxiliary blower controller  132  is responsive to the controller  124  to operate the auxiliary blower  84  via the motor  133  at a user selected blower speed when the auxiliary HVAC unit  30  is in the cooling mode  119 . The auxiliary blower controller  132  deactivates the auxiliary blower  84  when the auxiliary HVAC unit  30  is in the non-cooling mode  121  while the primary HVAC unit is in the cooling mode  118 . In this manner, there is no air flow to the rear portion  12  of the cabin  14 . It should be appreciated that the auxiliary blower controller  132  may be a separate component from the controller  124 , or the auxiliary blower controller  132  may represent computer code within the controller  124 . In other words, the controller  124  may be adapted to include the auxiliary blower controller  132 . 
   The control system  116  includes a primary blower controller  135  that is operatively connected to the controller  124 . The primary blower controller  135  actuates a motor  137  to rotate the primary blower  52 . The primary blower controller  135  is responsive to the controller  124  to operate the primary blower  52  when the primary HVAC unit  28  is in the cooling mode  118 . The primary blower  52  moves the cooled air into the front portion  10  of the cabin  14  when the primary HVAC unit  28  is in the cooling mode  118 . 
   The control system  116  includes an auxiliary actuator  130  that is operatively connected to the controller  124 . The auxiliary actuator  130  is responsive to the controller  124  to move or pivot the auxiliary mode door  86  between the first and second positions  87 , 88 . The control system  116  includes a first actuator  134  that is operatively connected to the controller  124 . The first actuator  134  is responsive to the controller  124  to move the first mode door  64  between the first and second positions  66 , 68 . The control system  116  also includes a second actuator  136  that is operatively connected to the controller  124 . The second actuator  136  is responsive to the controller  124  to move the second mode door  70  between the first and second positions  72 , 74 . The control system  116  also includes a third actuator  139  operatively connected to the controller  124  to move the intake door  56  between the positions  57 , 59  corresponding to drawing in the outside air and drawing in the air from the front portion  10 . 
   The primary and auxiliary HVAC units  28 , 30  may include primary and auxiliary heater cores  142 , 144  in addition to the primary and auxiliary evaporators  32 , 36 . It should be appreciated by those skilled in the art that the present invention may provide primary and auxiliary air conditioning units  138 , 140  having the evaporators  32 , 36  without the heater cores  142 , 144 . For clarity, the above description is directed toward the HVAC units  28 , 30 . However, the primary and auxiliary air conditioning units  138 , 140  may be used interchangeably for the HVAC units  28 , 30  while still accomplishing the present invention. In this instance, the primary and auxiliary air conditioning units  138 , 140  include all of the features and perform all of the functions of the primary and auxiliary HVAC units  28 , 30 . In other words, the heater cores  142 , 144  are not necessary to carry out the present invention. 
   The heater cores  142 , 144  are positioned in first and second coolant loops  146 , 148 . The first and second coolant loops  146 , 148  are interconnected and circulate coolant from an engine  152  through the heater cores  142 , 144 . A water pump  150  is used to circulate the coolant through the engine  152  of the vehicle  16  and into the first and second coolant loops  146 , 148 , as is well known in the art. 
   The heater cores  142 , 144  are disposed within the primary and auxiliary housings  50 , 82  downstream of the primary and auxiliary evaporators  32 , 36 . The heater cores  142 , 144  are separated from the evaporators  32 , 36  by primary and auxiliary air mixing doors  154 , 156 . The air mixing doors  154 , 156  include actuators  158 , 160  that are controlled by the controller  124  to move the air mixing doors  154 , 156 . Movement of the air mixing doors  154 , 156  is based on user-selected parameters such as temperature to control the temperature of the air entering the front and rear portions  10 , 12  of the cabin  14 . The primary and auxiliary blowers  52 , 84  move the air from the front and rear portions  10 , 12 , or alternatively, the primary blower  52  moves the outside air across the primary and auxiliary evaporators  32 , 36  and primary and auxiliary heater cores  142 , 144 , depending on the positioning of the air mixing doors  154 , 156 . The use and control of air mixing doors  154 , 156  to control air temperature are well known in the art and therefore, will not be described in detail. 
   An example of a method of cooling the air in the front and rear portions  10 , 12  of the cabin  14  of the vehicle  16  will now be described. It should be appreciated that the following example represents one of many ways in which the method of the present invention may be carried out. 
   To start, the method includes switching each of the primary and auxiliary HVAC units  28 , 30  from the non-cooling mode  120 , 121  to the cooling mode  118 , 119 . The compressor  38  is activated in response to the primary HVAC unit  28  being switched from the non-cooling mode  120  to the cooling mode  118 . The compressor  38  then begins to circulate the refrigerant through the primary HVAC unit  28  and the auxiliary HVAC unit  30  in response to activating the compressor  38 . The primary blower  52  is also activated to move the air across the primary evaporator  32  and transfer the heat from the air to the refrigerant to cool the air for the front portion  10  of the cabin  14  in response to the primary HVAC unit  28  being in the cooling mode  118 . The primary HVAC unit  28  then discharges the cooled air into the front portion  10  of the cabin  14  in response to activating the primary blower  52 . Specifically, the primary blower  52  moves air across the primary evaporator  32  to be cooled, then discharges the air through one of the plurality of primary air ducts  62  as selected by the user. 
   The auxiliary blower  84  is activated to move the air across the auxiliary evaporator  36  and transfer the heat from the air to the refrigerant to cool the air in the rear portion  12  of the cabin  14  in response to the auxiliary HVAC unit  30  being in the cooling mode  119 . The cooled air is transferred into the rear portion  12  of the cabin  14  in response to activating the auxiliary blower  84 . The user then switches the auxiliary HVAC unit  30  from the cooling mode  119  to the non-cooling mode  121  while the primary HVAC unit  28  remains in the cooling mode  118 . The auxiliary blower  84  is then shut down, i.e., power is discontinued to the motor  133  by the controller  124  and the cooled air is not discharged into the rear portion  12 . Simultaneously, the heater is automatically activated by the control system  116 , i.e., the controller  124  transmits the electrical output signal to the heater to begin raising the temperature of the heater. Again, this is in response to the auxiliary HVAC unit  30  being switched from the cooling mode  119  to the non-cooling mode  121  while the primary HVAC unit  28  remains in the cooling mode  118 . 
   The above described method is associated with an instance in which the user has requested cooled air for both the front and rear portions  10 , 12  of the cabin  14 , but then decides to stop cooling the rear portion  12 , i.e., by switching the auxiliary HVAC unit  30  to the non-cooling mode  121 . 
   In an alternative method, only the primary HVAC unit  28  is switched to the cooling mode  118  while the auxiliary HVAC unit  30  remains in the non-cooling mode  121 . In this instance, the method continues as described above, i.e., the compressor  38  is activated, the primary blower  52  is activated, the auxiliary blower  84  is deactivated, and the heater  90  is automatically activated. This alternative method can be associated with an instance in which the user has recently entered the vehicle  16  and only requests cooled air for the front portion  10 , i.e., by switching only the primary HVAC unit  28  to the cooling mode  118 . 
   It should be appreciated by those skilled in the air conditioning and refrigeration arts that the dual evaporator air conditioning system  20  of the present invention may be employed in non-automotive applications. For example, refrigeration systems such as food display cases, and residential air conditioning systems (mini-split, wall mounted room air conditioning units) may interconnect multiple evaporators with a common compressor. Therefore, the dual evaporator air conditioning system  20  of the present invention may be utilized as such. 
   Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.