In response to the problem of serious deterioration in the refrigeration performance of the heat pump air conditioning system at high temperatures, the impact of the electronic expansion valve of the new refrigerant R1234yf on the vehicle low-voltage air conditioning heat pump system was investigated with regard to its refrigeration performance. In order to ascertain the effect of refrigeration performance parameters at a high temperature of 50°C, the superheat of the main valve and the supplement valve was analyzed. To illustrate, when the primary valve was subjected to superheating by 3°C at a temperature of 9°C, the exhaust temperature exhibited an increase of 9.82°C, while the opening degree exhibited a decrease of 7.8%. In addition, both the evaporation temperature and condensing temperature decreased by 3.97°C and 11.25°C, respectively. When the primary valve was subjected to superheating by 5°C, the maximum refrigeration and COP were 3.201 kW and 1.769, respectively. This represents an increase of 13.96% and 10.91%, respectively. Upon the increase of the supplement excess heat by 15°C, the exhaust temperature exhibited an increase of 7.23°C, while the opening degree demonstrated a decrease of 20.7%. The evaporation temperature and condensing temperature have decreased by 1.8°C and 6.15°C, respectively. When the auxiliary valve was superheated at 10°C, the cooling capacity and COP were 3.315 kW and 1.889, respectively. The values in question exhibited an increase of 3.01% and 7.51%, respectively, in comparison to the baseline conditions. The optimal temperature for the main valve is 5°C, while the optimal temperature for the auxiliary valve is 10°C.