Control apparatus for refrigerated cargo container

A method of controlling the temperature inside a mobile cargo container that is equipped with a refrigeration unit for supplying chilled air to the container, the method including:

• providing an adjustable control valve in a suction line lead to the refrigeration unit compressor, said valve being adjustable in uniform increments between a fully opened and a fully closed position,
• periodically sensing the temperature of the supply air being discharged from the refrigeration unit into the container at given intervals,
• comparing the sensed temperature to a predetermined set point temperature to determine the amount of deviation between the two temperatures,
• fully opening the control valve when the amount of deviation is greater than a first value whereby the supply air temperature is changed at a fast rate,
• adjusting the control valve a first number of increments during each sensing interval when the amount of deviation is between said first value and a second lesser value whereby the supply air temperature is changed at an intermediate rate,
• adjusting the control valve a second lesser number of increments during each sensing interval when the amount of deviation is less than said second value whereby the supply air temperature is changed at a relatively slow rate, and
• monitoring the valve position and activating a heater in the supply air flow when the valve approaches a fully closed position.