In theory

using internal heat exchanger in the R134a vehicle air conditioning system can improve the cooling performance significantly，but many experimental studies demonstrates that the internal heat exchanger has a negative effect on the safety of the system. Therefore the advantage and the disadvantage trade off

which makes the merit not conspicuous. Aimed at this situation

the influence of different length of internal heat exchanger on the air conditioning system comprehensive performance is investigated in test bench in this paper. It shows that the adverse effects have certain relationships with the tube length on the basis of the experiments. In addition

this study also obtain a method to avoid adverse effects

by adjusting the expansion valve

condenser air flow and oil

which provides theoretical foundation for the matching of heat regeneration system.