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A method of conditioning air in a vehicle load space. The method includes providing a refrigeration circuit including an evaporator, directing refrigerant through the refrigeration circuit, directing load space air across the evaporator, sensing a first condition based on one of a temperature and a

A method of conditioning air in a vehicle load space. The method includes providing a refrigeration circuit including an evaporator, directing refrigerant through the refrigeration circuit, directing load space air across the evaporator, sensing a first condition based on one of a temperature and a pressure of the refrigerant in the refrigeration circuit upstream from the evaporator, determining a second condition based on one of a temperature and a pressure of the refrigerant in the evaporator, determining a difference between the first condition and the second condition, and initiating a defrost process of the evaporator when the difference is greater than a threshold.

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1. A method of conditioning air in a vehicle load space, the method comprising the acts of: providing a refrigeration circuit including an evaporator and a throttle valve;directing refrigerant through the refrigeration circuit;directing load space air across the evaporator;sensing a first condition,

1. A method of conditioning air in a vehicle load space, the method comprising the acts of: providing a refrigeration circuit including an evaporator and a throttle valve;directing refrigerant through the refrigeration circuit;directing load space air across the evaporator;sensing a first condition, the first condition being a function of one of a temperature and a pressure of the refrigerant in the refrigeration circuit away from the evaporator;measuring one of a temperature and a pressure of the refrigerant in the evaporator;using the one of the temperature and the pressure of the refrigerant in the evaporator to determine a second condition;determining a position of the throttle valve;determining a difference between the first condition and the second condition;initiating a defrost process of the evaporator in response to the throttle valve in a fully open position and the difference being greater than a threshold; and determining a saturation suction temperature; comparing the saturation suction temperature with an evaporator coil temperature; and initiating the defrost process in response to the saturation suction temperature being less than the evaporator coil temperature. 2. The method of claim 1, wherein sensing the first condition comprises measuring the one of the temperature and the pressure of the refrigerant at the throttle valve, the method further comprising determining a conversion process based on the one of the temperature and the pressure of the refrigerant at the throttle valve; andusing the conversion process and the one of the temperature and the pressure of the refrigerant at the throttle valve to determine the first condition. 3. The method of claim 2, wherein the conversion process comprises one of converting one of the temperature and the pressure of the refrigerant at the throttle valve to the other of the temperature and the pressure, and determining one of the temperature and the pressure with a curve-fitting formula. 4. The method of claim 1, further comprising monitoring a quantity of the refrigerant in the refrigeration circuit and preventing initiation of the defrost process when the quantity of the refrigerant in the refrigeration circuit is below a predetermined value. 5. The method of claim 1, wherein the refrigeration circuit includes a compressor having a full capacity, and further comprising operating the compressor substantially at full capacity before initiating the defrost process. 6. The method of claim 1, further comprising: determining a position of the throttle valve; andinterrupting the defrost process of the evaporator when the electronic throttle valve position is less than fully opened. 7. The method of claim 1, further comprising determining a temperature range for the load space air;sensing a temperature of the load space air; andpreventing initiation of the defrost process when the temperature of the load space air is below the temperature range. 8. A system for conditioning air in a load space of a vehicle, the system comprising: a refrigeration circuit including an evaporator and housing refrigerant, the refrigeration circuit further including a throttle valve upstream of the evaporator;a first sensor positioned along the refrigeration circuit to sense a first condition, the first condition being a function of one of a temperature and a pressure of the refrigerant in the refrigeration circuit away from the evaporator;a second sensor positioned along the evaporator to sense one of a temperature and a pressure of the refrigerant in the evaporator;a controller determining a second condition based on the one of the temperature and the pressure of the refrigerant in the evaporator and to convert the one of the temperature and the pressure of the refrigerant in the refrigeration circuit away from the evaporator to determine the first condition, the controller further configured determine a position of the throttle valve, determining a difference between the first condition and the second condition, and initiating a defrost process of the evaporator in response to the throttle valve in a fully open position and the difference being greater than a threshold and wherein the controller determines a saturation suction temperature and to compares the saturation suction temperature with an evaporator coil temperature, and wherein the controller initiates the defrost process in response to the saturation suction temperature being less than the evaporator coil temperature. 9. The system of claim 8, wherein the controller is further configured to interrupt the defrost process of the evaporator when the electronic throttle valve position is less than fully opened. 10. The system of claim 8, further comprising a third sensor positioned along the refrigerant circuit to sense a quantity of the refrigerant in the refrigeration circuit, and wherein the controller is configured to determine if the quantity of the refrigerant is greater than a charge threshold and to prevent initiation of the defrost process when the quantity of the refrigerant in the refrigeration circuit is below the charge threshold. 11. The system of claim 8, further comprising a load space temperature sensor in thermal communication with the load space to determine a temperature of the air in the load space, and wherein the controller is further configured to store a set point temperature, to determine a difference between the temperature of the air in the load space and the set point temperature, and to prevent initiation of the defrost process when the temperature is below the set point temperature. 12. The method of claim 1, further comprising terminating the defrost process;determining a position of the throttle valve after the defrost process has been terminated; andmonitoring a quantity of the refrigerant in the refrigeration circuit based on the position of the throttle valve. 13. The method of claim 12, further comprising determining the throttle valve in the fully open position, the fully open position indicative of a low quantity of refrigerant in the refrigeration circuit; andinitiating an alarm in response to the throttle valve in the fully open position. 14. The method of claim 12, further comprising determining the throttle valve in a less than fully open position, the less than fully open position indicative of an acceptable quantity of refrigerant in the refrigeration circuit. 15. The system of claim 8, wherein the controller is configured to monitor a quantity of refrigerant in the refrigeration circuit based on the position of the throttle valve, and wherein the controller is configured to initiate a low refrigerant alarm in response to the throttle valve being in the fully open position. 16. A system for conditioning air in a load space of a vehicle, the system comprising: a refrigeration circuit including an evaporator and housing refrigerant, the refrigeration circuit further including a throttle valve located upstream of the evaporator;a first sensor positioned along the refrigeration circuit adjacent the throttle valve to sense a first condition of the refrigerant in the refrigeration circuit;a second sensor positioned adjacent the evaporator to sense a second condition of the refrigerant in the evaporator; anda controller determining a position of the throttle valve, a saturation suction temperature, and a difference between the first condition and the second condition, the controller further determining an evaporator coil temperature based on the second condition and initiaing a defrost process of the evaporator in response to the throttle valve in a fully open position, the saturation suction temperature being less than the evaporator coil temperature, and the difference being greater than a threshold. 17. The system of claim 16, further comprising a third sensor in thermal communication with the load space to determine a temperature of the air in the load space, the controller further configured to determine a difference between the temperature of the air in the load space and a set point temperature, and to prevent initiation of the defrost process when the temperature of the load space air is below the set point temperature.