Komatsu 830E-AC Shop Manual page 935

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
temperature lower than another, this heat
transfer will occur.
• Temperature is the measurement of the intensity
of heat in degrees. The most common measuring
device is the thermometer.
• All liquids have a point at which they will turn to
vapor. Water boiling is the most common
example 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
process. 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.
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, pressur-
izes the heat laden refrigerant and forces it through
the discharge valve (high side) on to the condenser.
N04031 10/06
Ambient air, passing through the condenser removes
heat from the circulating refrigerant resulting in the
conversion 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,
adding 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 evapora-
tor and drops into the drain pan from which it drains
out of the cab.
Refrigerant leaving the evaporator enters the accu-
mulator. The accumulator functions as a sump for liq-
uid refrigerant in the system. Because of its design,
the accumulator only allows vaporized refrigerant to
return to the compressor, preventing compressor
slugging from occurring. Desiccant is located at the
bottom of the accumulators to remove moisture that
is trapped in the system.
The cycle is completed when the heated low pres-
sure gas is again drawn into the compressor through
the suction side.
This simplified explanation of the principles of refrig-
eration does not call attention to the fine points of
refrigeration technology. Some of these will be cov-
ered in the following discussions of the components,
controls, and techniques involved in preparing the
unit for efficient operation.
Operator Comfort N4-9