Transport refrigeration system with secondary condenser and maximum operating pressure expansion valve

A transport refrigeration system which maintains a predetermined set point temperature of a served space via cooling and heating cycles which condition air passed through an air conditioning path of an evaporator section of a refrigeration system which includes a refrigerant disposed in a closed refrigerant circuit having a first active circuit effective during a cooling cycle which includes a compressor, a hot gas line, a condenser, a receiver, a liquid line, an evaporator, an accumulator, and a suction line, and a second active circuit effective during a heating cycle which excludes the condenser and receiver, the improvement comprising:

• an expansion device disposed between the liquid line and the evaporator, dividing the refrigeration system into a high pressure side which includes the condenser and receiver, and a low pressure side which includes the evaporator, accumulator and the suction line which has a suction pressure,
• said expansion device being a maximum operating pressure valve which closes at a predetermined pressure,
• a secondary condenser disposed in the air conditioning path of the evaporator section,
• valve means operable to direct hot gas from the compressor to the secondary condenser during a heating cycle, which increases the pressure of the low pressure side,
• said expansion device closing in response to low side pressure, when there is sufficient refrigerant in the second active circuit to cause the pressure of the low side to increase to the predetermined closing value,
• said expansion device injecting refrigerant into the evaporator from the receiver and condenser when the refrigerant in the second active circuit is insufficient to close the expansion device and the suction pressure is lower than the high side pressure