When the rail vehicle air-conditioning equipment is operated at high ambient air temperature, it is an important task to prevent abnormal rise of head pressure and refrigerant temperature leaving the compressor.
This paper gives the results of a study on a new overload relieving system based on a hot liquid bypass method in order to indicate how to accomplish the task.

The new overload relieving system patent pending in Japan, U.S.A. and U.K. consists of a liquid bypass method which connects the high pressure liquid line to the compressor suction line, together with the evaporator dividing method.

Compared with the conventional unload method, the new system is effective, especially in decreasing refrigerant temperature leaving the compressor. By applying the overload relieving system based on the new method, the operation of air-conditioning equipment at 55°C ambient air temperature becomes feasible.