Abstract: There is a "breathing effect" in the refrigerating operation of refrigerator, and the air between the inside and outside of the refrigerator will exchange heat and mass with the "breathing effect". Through the method of pressure difference experiment, studies the influence of the switch of fan, damper and compressor and the change of refrigerator penetration state on the formation mechanism of differential pressure during the refrigeration process of single-cycle frost-free refrigerator. It has been proved that by closing the frost drain pipe, the way of the outside high temperature and high humidity air entering the refrigerator can be changed, the air intake volume of the refrigerator can be increased, and the path of the outside air entering the refrigerator can be extended, so as to improve the relative humidity of the refrigerator room, which is beneficial to the freshness preservation of vegetables and fruits, and at the same time, energy saving and emission reduction.

Key words: Air pressure difference, Refrigerator performance, Frost-free Refrigerator, Breathing effect, Heat and mass exchange