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Modern Refrigeration and Air Conditioning
and an evaporator. The main differences between a
small tabletop refrigerator and a building rooftop unit
are the size of the components and the controls used.
These four basic components are joined together by
tubing to create a circle (circuit), or what is commonly
referred to as the refrigerant loop.
Figure A illustrates the basic refrigeration sys-
tem showing the four basic components as they are
arranged in a typical system. The refrigerant flow path
can be thought of as a continuous circular flow. As
you will learn from studying the refrigerant loop, heat
always flows from hot to less hot. The complete cycle
can be traced as the refrigerant vapor flows from the
compressor (the hottest point in the system) through
the condenser, then through the metering device, into
the evaporator (less hot or cold), and back again into
the compressor. Follow this path as illustrated by the
arrows in the schematic shown in Figure A. All refrig-
eration and air-conditioning systems pump the refrig-
erant vapor that removes heat from the area around
the evaporator and rejects this heat at the condenser.
Chapter 2, Basic Refrigeration Systems, describes this
basic process in more detail.
Color Code
Throughout Modern Refrigeration and Air
Conditioning, color coding is provided to illustrate
the refrigerant flow through a system and to guide
your understanding of the cycle. You can see where
color coding is used to signify the difference between
liquid (dark) and vapor (light). High temperature and
pressure are shown as red. Low temperature and pres-
sure are shown in blue. An easy-to-use key is included
at the bottom of each illustration that uses a color code.
Refer back to Figure A to see the color code at the bot-
tom of the illustration.
Condenser
Metering device
Evaporator
Compressor
Low-pressure vapor
Low-pressure liquid
High-pressure vapor
High-pressure liquid
Figure A. Refrigeration systems include four primary components: a compressor, a condenser, a metering device, and an
evaporator. The condition or state of the refrigerant changes at each component as it travels through the refrigerant loop.