Temperature control system and method of operating the same

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.