Abstract: With the development of household air conditioning, for some special scenarios, such as the base station room, Internet cafe, wine cellar, kitchen, etc., the indoor temperature is high and the outdoor side temperature is low, so it needs to have a low-temperature refrigeration function. Under the working conditions of 21℃ and 32℃ on the inner side, test and verify the working conditions of 12℃, 4℃, -2℃, -10℃ and -15℃ on the outer side respectively, and analyze the oil return and liquid return in combination with the phenomenon of the liquid sight glass of the compressor. It is confirmed that the liquid storage tank of the compressor needs to be able to accommodate more than 65% of the refrigerant mass. For refrigeration under the low-temperature working conditions on the outer side, it is necessary to ensure that the superheat at the bottom of the compressor is above 5℃,for the high-temperature working conditions, it is necessary to pay attention to whether the pressure will exceed the standard. By adjusting the frequency of the compressor, the speed of the external fan and the opening of the expansion valve, the superheat can be increased and the pressure can be reduced to avoid liquid return.

Key words: Low-temperature refrigeration, Superheat, Return liquid, Liquid hammer, Reliability