Figure 4-10.-FIoor-mounted air-conditioning unit (shown with
cover panels removed).
Cooling equipment for air conditioning must be of
a type that will satisfactorily cool the air for a particular
space that is being air conditioned. One method used to
cool air in air-conditioning units is to evaporate water.
A discussion of this method, called evaporative cooling,
can be found in chapter 10 of the UT3 TRAMAN.
Another method, and one of the most important, is
mechanical refrigeration. In this method, the air that
is to be conditioned and cooled is blown through cooling
coils having a temperature of about 50°F. This not only
cools, but dehumidifies the air. A discussion of this
method can also be found in chapter 10 of the UT3
There are various types of air-conditioning units and
systems. A few of the common types are discussed
Self-Contained (Package) Units
Self-contained refrigerative air-conditioning units
are either window units (figs. 4-8 and 4-9) or larger
Figure 4-11.-Refrigerating cycle of a package type air-
floor-mounted units (fig. 4-10). Both types of units
contain a complete system of refrigeration components.
The window units need not be installed in windows.
They also can be installed in transoms, or they can be
framed into outside walls. The use of outside walls is
important for proper performance. When the unit is
operating, the compressor (fig. 4-11) forces a high-
-pressure (high-temperature) refrigerant gas to the
condenser. The condenser fan draws in and blows
outside air over the condenser coils. This movement of
the relatively cooler outside air over the hot condenser
coils changes the gas to a liquid, giving off heat that is
exhausted to the outside. The liquid then passes through
a control device that regulates the flow of the liquid to
the evaporator. In the evaporator, the liquid changes to
a low-pressure (low-temperature) gas that is circulated
through the evaporator coils. The inside or room air is
then circulated by an evaporator fan over the cold
evaporator coils. This action removes heat from the air
and returns the cooled air back to the room.
A variation of this type of unit is the heat pump. In
a heat pump, the roles of the condenser and the
evaporator can be reversed so that the unit draws in and
heats outside air and expels cold inside air. In this way,
the unit functions as a heating unit, rather than a cooling