Thermal expansion valve system.
COMPRESSOR:
The Compressor transports the refrigerant at the required pressure
through the air conditioning system. The refrigerant is a low pressure
gas as it enters the Compressor from the Evaporator. The Compressor
increases the refrigerant pressure and also its temperature so it
becomes a high pressure gas which, in turn, helps the refrigerant
condense more rapidly in the next component, which is the Condenser.
The Compressor is mounted on the engine and is driven by a belt from the
engine's crankshaft pulley. The most common reasons for failure are
lack of oil, pulley bearing wear, electromagnetic coil burn-out and lack
of regular servicing.
CONDENSER:
The Condenser works in the opposite way to the Evaporator. The
refrigerant gives up its heat generated by the Compressor by passing
cold air across its fins and tubes by ram air or by an extra fan. The
end result of this change is that the refrigerant is now a high pressure
liquid and is forced out to the Receiver Drier through the liquid line.
Because the Condenser is usually located at the front of the vehicle it
can become damaged by debris or corroded by materials from the road.
It can also fail because of weak spots in its construction and also lack
of regular servicing.
FILTER DRIER:
Depending on the type of air conditioning system fitted, this item can
be called a Receiver Drier or an Accumulator. (The Accumulator is
fitted on the low pressure gas line of an air conditioning system
between the Compressor and the Evaporator and is used in conjunction
with an orifice tube). The Receiver Drier is fitted on the high
pressure liquid line of an air conditioning system between the Condenser
and Expansion Device. The Receiver Drier has two parts to it, the
receiver and, of course, the drier. The receiver section holds the
right amount of refrigerant required by the system to ensure correct
operation and to supply a steady flow of liquid refrigerant to the
Expansion Device. The drier section is responsible for removing
moisture from the air conditioning system by means of a bag of desiccant
which absorbs small quantities of moisture. This is a very important
part of the air conditioning system and should be changed at least every
two years or when the system is repaired. The most common reasons for
failure is corrosion and desiccant deterioration which leads to severe
system failure.
EXPANSION DEVICE:
The Expansion Device comes in many forms. It can be a brass internally
or externally equalised valve, a block type valve or an orifice tube
(the latter being part of an Accumulator type air conditioning system).
Expansion Device's have an inlet and an outlet which separates the high
side of the system from the low side. A small restriction in the valve
allows only a small amount of refrigerant to pass through it into the
Evaporator, the amount of refrigerant passing through the valve depends
on the Evaporator temperature. The most common reasons for failure are
contamination, moisture and lack of regular servicing.
EVAPORATOR:
As soon as the liquid pressure drops, the refrigerant begins to boil
(R134A refrigerant boils at approximately -26 degrees centigrade). As
it continues to boil the Evaporator absorbs the heat passing over its
tubes and fins and as a result the air is cooled. Remember that heat
is being removed from the warm air and cold air is not being created.
The compressor, on its suction side, removes the low pressure vapour
from the Evaporator and the cycle starts all over again. The most
common reasons for failure are corrosion, weak spots in construction and
lack of regular servicing.