Abstract: In a transport temperature control system having a cooling and heating mode of operation an apparatus and method are provided for enhancing the heating capacity during the heating mode of operation. A second expansion valve is provided to connect the higher pressure liquid line to the refrigerant circuit downstream of the evaporator. When additional refrigerant is needed in the heating circuit to increase heating capacity, especially during low ambient temperature operating conditions, the second expansion valve is caused to open to admit more refrigerant to the system. After passing through the second expansion valve low pressure gas is passed to the compressor, optimizing compressor efficiency such that an increased amount of hot refrigerant gas is delivered to the evaporator for enhanced heating capacity.

Abstract: A transport refrigeration system which includes a compressor, a condenser, a receiver, an evaporator, an accumulator, and a control valve having cooling and heating output ports which are alternatively connected to first or second refrigerant circuits to initiate cooling and heating cycles, respectively. The heating capacity of a commanded heating cycle is enhanced prior to switching to the heating cycle by connecting the outlet of the receiver to the second refrigerant circuit while maintaining the control valve cooling port active in the first refrigerant circuit for a predetermined time delay. This forces liquid refrigerant in the condenser to flow into the receiver and then into the second refrigerant circuit, making additional liquid refrigerant available to the heating cycle, which is initiated at the end of the predetermined time delay, without introducing liquid refrigerated directly into the accumulator.