In order to avoid the summer system operation, the evaporation temperature of the system exceeds the following limits normally allowed by such compressors, the design evaporation temperature of the air conditioner evaporator must be made. Obviously, the efficiency of the air conditioner refrigeration operation will decrease as the evaporation temperature decreases; The price of this kind of compressor is higher than that of air-conditioner compressor. Therefore, it is really necessary to consider whether it is necessary to pay such a high price, so that the air conditioner can barely operate under the condition that there is no economic and technical advantage at all. If the air compressor is simmered after the air intake is unloaded, the oil of the upper jaw will enter the intake passage of the engine, affecting the engine's emission index. This is undoubtedly not allowed today when environmental protection is increasingly being valued by humans. Therefore, no matter which unloading mode is adopted for the air compressor, there are disadvantages in the supercharged intake air.

In addition, most of the room air conditioners currently use capillary throttling elements, the capillary structure is simple and reliable, but the ability to adapt to load changes is relatively poor. To compensate for this shortcoming, many heat pump air conditioners are used in cold air systems. Based on the configured main capillary, the auxiliary capillary is added in series with the main capillary to change the throttling parameters, so that the throttling system has two parameters to adapt to the two modes of operation.

Compared to the cooling operation, the heat pump has a much larger operating range. Obviously, the operating range will be expanded and the thermal efficiency will be greater throughout the operating range. Therefore, to expand the operating range of the system must fully consider the outdoor temperature range in which a reasonable working range is arranged. If the best working point is moved to a lower temperature point, it will inevitably lead to the heat pump system in the working range which usually has a strong advantage. The operating efficiency is reduced, and the optimal operating point of a typical heat pump system is under conditions where the outdoor air temperature is suitable.