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When the hot refrigerant vapor discharged from the compressor travels through the condenser, the cool
air or water flowing through the condenser coil absorbs enough heat from the vapor to cause it to
condense.
If the outside air temperature is 27° C, an air cooled system is designed so that the temperature of the
refrigerant, right at the point where it first condenses, will be about 40°C to 46°C. If the entering condenser
water temperature is 30°C, a water-cooled system is designed so that the temperature of the refrigerant,
right at the point where it first condenses, will be about 40°C.
Why do we want the refrigerant to condense at this relatively high temperature? So that the air or water
flowing through the condenser will be very cold relative to the temperature of the discharge vapor, Which
will allow the heat energy in the vapor to move into that relatively cold air or water, And cause the
refrigerant to condense.
At this stage in the refrigeration cycle, high pressure liquid refrigerant will flow down the liquid line,
through a filter drier that is designed to prevent contaminants from flowing through the system, and on to
the metering device.
The metering device, component #3 on this refrigeration cycle diagram, is the dividing point between the
high pressure and low pressure sides of the system, And is designed to maintain a specific rate of flow of
refrigerant into the low side of the system.
If the wrong capacity of metering device is used, or if there is a problem with the metering device, An
incorrect quantity of refrigerant will flow into the evaporator.
When the high-pressure liquid refrigerant passes through the metering device, its pressure will drop to a
low pressure that will be equivalent to about 6°C to 9°C below the design temperature of the evaporator. It
starts evaporating immediately, and it wouldn't be too inaccurate to imagine it acting like warm soda when
you shake the bottle and pop the top off. It shoots out into the evaporator foaming, bubbling, and boiling,
And remember, it's at a low pressure, so for a freezer it would be boiling at about -23°C to -26°C and for a
medium temperature refrigerator it would be boiling at about -4°C.
And that brings us to the evaporator, component #4 in the refrigeration cycle diagram. There will be
relatively warm air (or water, if the unit is an ice machine) flowing over the evaporator coil.
The refrigeration system is designed so that the refrigerant will evaporate in the evaporator at a
temperature that's about 6°C to 9°C below the temperature setting if it's a refrigerator or freezer, and the
temperature will drop to around -18°C in the evaporator of an ice machine or ice cream machine.
The system is designed so that the heat in the relatively warm air flowing over the evaporator will move
into the cold evaporating refrigerant.
This process will continue to cool the air that's flowing over the evaporator until it reaches the design set
point or thermostat setting.
So, when you turn on the refrigerator, freezer, ice machine or ice cream machine, the system is designed
so that the evaporator will stay colder than whatever it's cooling, and will continuously remove heat from
it and cool it.
Version 2.6
Page 8 of 20
1st June 2021
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