vapor and the liquid must be separated before the vapor
Some of the advantages of R-12 are as follows:
can be superheated.
It is nonflammable, nonexplosive, and non-
TEMPERATURE--A measure of the heat
corrosive.
intensity or concentration of heat (thermal energy) in a
Its vapor is nontoxic.
body or substance, measured in degrees.
At the low-pressure point of its cycle, it operates
REFRIGERATION TON--The transfer of heat
at pressures slightly above atmospheric pres-
at a rate of 288,000 Btu in 24 hours (12,000 Btu in 1
sure. This minimizes the possibility of air
hour).
entering the system.
VACUUM--Any pressure less than atmospheric
At the high-pressure point of its cycle, pressure
pressure.
is relatively low. This allows the use of light-
VAPOR--The gaseous form of any substance.
weight equipment.
Vapor condenses very readily to a liquid state under
small changes of temperature or pressure, or both. It
Refrigerant 22 (R-22)
may be said to be very close to the liquid state, although
it is a vapor.
R-22, like R-12, is a member of the fluorinated
hydrocarbon family. Its chemical name and symbol,
REFRIGERANTS
monochlorodifluoromethane (CHClF2), indicate that
R-22 contains one part carbon, one part hydrogen, one
A refrigerant is a substance that can easily be
part chlorine, and two parts fluorine.
changed from a liquid state to a vapor state. Ideally, it is
At atmospheric pressure, R-22 boils at -41F. Its
a substance with a low boiling point. It must also have
latent heat of vaporization is about 92 Btu per pound.
the ability to absorb and carry heat at a low temperature.
This ability to absorb great amounts of heat, combined
Finally, it must be able to transfer this absorbed heat to
with its low boiling point, makes R-22 a very good
a cooling medium as it condenses.
refrigerant for systems of high capacity and low
Most refrigerants in use today require relatively
temperatures.
low operating pressures within the system. Heavy con-
R-22 requires higher pressures in its cycle than
struction is not required and the problem of leaking is
R-12. As a result, slightly heavier construction is
minimized.
required. With this exception, all the advantages
To prevent confusion and provide for a standard
associated with R-12 also apply to R-22.
system, all refrigerants are assigned numbers instead of
One inherent disadvantage that is shared by both
trade names. They are referred to as refrigerant 12,
R-12 and R-22 is their capacity to absorb water. If not
refrigerant 22, and so on.
controlled, moisture in the refrigerant can cause two
Here, we will discuss refrigerant 12, for back-
serious problems. First, moisture reacts chemically
ground information, and refrigerant 22, because that is
with the refrigerant to form hydrochloric acid, which is
the type currently used in the A/M32C-17 and the
a very corrosive substance. Second, moisture in the
A/M32C-21 air-conditioners.
refrigerant tends to freeze, which can have a serious
effect on system components, such as expansion valves.
Refrigerant 12 (R-12)
In most air-conditioning systems, chemical driers are
used to control the level of moisture in the refrigerant.
Research for the perfect refrigerant resulted in
R-12. It approaches that ideal more than any other
Other Refrigerants
refrigerant discovered so far. Its chemical name and
symbol, dichlorodifluoromethane (CCl2F2), indicate
You should be aware that there are other
that R-12 contains one part carbon, two parts chlorine,
refrigerants on the market (R-134A for one) that are not
and two parts fluorine.
compatible with systems using R-22. Such other
refrigerants are blends of existing refrigerants and, in
At atmospheric pressure, R-12 boils at -21.66F. Its
some cases, are highly flammable. Some of these blend
latent heat of vaporization is about 72 Btu per pound.
refrigerants may break down the desiccant in the
This means that as R-12 changes state to a vapor, it
receiver/drier and pass the debris into the rest of the
absorbs 72 Btu per pound.
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