Domestic refrigerators and freezers do not employ a mechanical device as a refrigerant flow control. Instead a capillary restrictor meters refrigerant liquid to the evaporator and maintains a pressure differential whilst the compressor is operating.
Basically the capillary restrictor is a small tube. The refrigerant flow rate is determined by the length of the tubing and the internal diameter of the bore. Refrigerant will continue to flow through the capillary when the compressor stops until the pressures in the system (high side and low side) equalize.
The capillary is normally located after the filter drier; it is sometimes formed into a tight coil around the suction line. Figure 56 shows a typical domestic refrigerator arrangement. It will be noted that the capillary actually passes through the inside of the suction line to the evaporator and thereby provides a heat exchange feature which improves compressor performance.
Suction line accumulators are employed to prevent frosting back along the suction line after off cycles. This is because the relatively small refrigerant charges in modern refrigerators and freezers are difficult to control accurately, and some overspill from the evaporator occurs when the compressor stops.
Accumulators are shown in Figures 52-55.
Freezer door heater and oil cooler
Figure 57 shows a freezer system diagram with door frame heater and oil pre-cooler.
Hot gas defrosting
Figure 58 shows the normal refrigeration and defrost cycles in an appliance using hot gas defrosting.
Solenoid flow control for refrigerator/freezer
Figure 59 shows the refrigeration system and Figure 60 the electrical circuit for solenoid flow control.
When the refrigerator thermostat is made and the freezer thermostat is open circuit, the relay is energized through contacts 1 and 3. The compressor operates but the solenoid is not energized, and the refrigerant flows through the refrigerator evaporator and the freezer evaporator.
When the freezer thermostat is made and the refrigerator thermostat is open circuit, the compressor operates and the solenoid is energized through contacts 1 and 2. The refrigerator evaporator is by-passed.
When the refrigerator thermostat makes whilst the compressor is operating, the relay is energized. This opens contacts 1 and 2, and refrigerant will again flow to the refrigerator evaporator as well as the freezer evaporator.