3.2 REFRIGERATION SYSTEM
All refrigeration units cool by removing heat from the cabinet rather than pumping in cool air. In
a conventional refrigeration unit, liquid refrigerant enters the evaporator and vaporizes (boils)
due to the low pressure, creating a very cold surface which removes heat from inside the cabinet.
This causes the refrigerant to boil (evaporate) into a vapor state and be drawn into the
compressor. The compressor pressurizes the vapor and pumps it into the condenser. The hot
vapor in the condenser gives off the heat into the room. As the vapor cools, it condenses back
into a liquid and returns to the evaporator to start the process over again. The system
continually soaks up the heat inside the refrigerator and deposits the heat back into the room.
The compressor of the refrigeration system serves two purposes: it ensures movement
of the refrigerant throughout the system and it increases the pressure and temperature of
the vapor received from the suction line and pumps the refrigerant into the discharge line.
The condenser receives this high temperature, high pressure refrigerant and allows the
heat to be released into the cooler surroundings. This heat removal "condenses" the
refrigerant vapor into a liquid.
The hot pipe is the first part of the condenser routed around the cabinet to help prevent
moisture formation.
The filter dryer is installed at the end of the condenser to capture moisture which may be
present in the system.
The capillary tube meters the flow of refrigerant and creates a pressure drop. Size and
length of the capillary is critical to the efficiency of the system.
As the refrigerant leaves the capillary tube and enters the larger tubing of the evaporator,
the sudden increase in tubing diameter, and the pumping action of the compressor, form
a low pressure area. The temperature of the refrigerant drops rapidly as it changes to a
mixture of liquid and vapor. In the process of passing through the evaporator, the
refrigerant absorbs heat from the storage area and is gradually changed from a liquid and
vapor mixture (saturated refrigerant) into a vapor.
The suction line returns this low pres-sure vapor from the evaporator back to the
compressor, and the cycle starts again.
Part of the capillary tube is soldered to the suction line which forms a heat exchanger.
Heat from the capillary tube is thus transferred to the suction line to superheat the
refrigerant there and at the same time this further cools the liquid in the capillary tube.
This cools the refrigerant before it enters the evaporator and also heats the refrigerant
before it enters the compressor to ensure a vapor state.
