Refrigeration Process - EdgeStar CWB8420DZ Service Manual

2.2 Refrigeration Process

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 due to the
low pressure, creating a very cold surface which removes heat from inside the cabinet. This causes
the refrigerant to boil 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.
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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 pressure 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.