Komatsu 830E Shop Manual page 559

REFRIGERATION - THE ACT OF COOLING
•
There is no process for producing cold; there is
only heat removal.
•
Heat always travels toward cooler temperatures.
This principle is the basis for the operation of a
cooling unit. As long as one object has a tem-
perature lower than another, this heat transfer
will occur.
•
Temperature is the measurement of the intensity
of heat in degrees. The most common measur-
ing device is the thermometer.
•
All objects have a point at which they will turn to
vapor. Water boiling is the most common exam-
ple of heating until vapor is formed. Boiling is a
rapid form of evaporation. Steam is a great deal
hotter than boiling water. The water will not
increase in temperature once brought to a boil.
The heat energy is used in the vaporization pro-
cess. The boiling point of a liquid is directly
affected by pressure. By changing pressure, we
can control the boiling point and temperature at
which a vapor will condense. When a liquid is
heated and vaporizes, the gas will absorb heat
without changing pressure.
•
Reversing the process, when heat is removed
from water vapor, it will return to the liquid state.
Heat from air moves to a cooler object. Usually
the moisture in the cooled air will condense on
the cooler object.
•
Refrigerant - Only R-134a should be used in the
new mobile systems which are designed for this
refrigerant.
M09010 05/02
THE REFRIGERATION CYCLE
In an air conditioning system, the refrigerant is circu-
lated under pressure through the five major compo-
nents in a closed circuit. At these points in the system,
the refrigerant undergoes predetermined pressure and
temperature changes.
The compressor (refrigerant pump) takes in low pres-
sure heat laden refrigerant gas through the suction
valve (low side), and as its name indicates, pressurizes
the heat laden refrigerant and forces it through the dis-
charge valve (high side) on to the condenser.
Ambient air, passing through the condenser removes
heat from the circulating refrigerant resulting in the con-
version of the refrigerant from gas to liquid.
The liquid refrigerant moves on to the receiver drier
where impurities are filtered out, and moisture
removed. This component also serves as the tempo-
rary storage unit for some liquid refrigerant.
The liquid refrigerant, still under high pressure, then
flows to the expansion valve. This valve meters the
amount of refrigerant entering the evaporator. As the
refrigerant passes through the valve, it becomes a low
temperature, low pressure liquid and saturated vapor.
This causes the refrigerant to become cold.
The remaining low pressure liquid immediately starts to
boil and vaporize as it approaches the evaporator, add-
ing to the cooling. The hot, humid air of the cab is
pulled through the evaporator by the evaporator
blower. Since the refrigerant is colder than the air, it
absorbs the heat from the air producing cool air which
is pushed back into the cab. The moisture in the air
condenses upon movement into the evaporator and
drops into the drain pan from which it drains out of the
cab.
The cycle is completed when the heated low pressure
gas is again drawn into the compressor through the
suction side.
This simplified explanation of the principles of refrigera-
tion does not call attention to the fine points of refriger-
ation technology. Some of these will be covered in the
following discussions of the components, controls, and
techniques involved in preparing the unit for efficient
operation.
Air Conditioning System
for HFC 134a Refrigerant
M9-3