We all know about air conditioning system. The automotive air conditioning system is also works on the reverse Brayton or Rankine cycle. As like all air
conditioning system the aim of automotive air conditioning is to control the temperature
and humidity of the atmospheric air and circulate the same in the automobile. The
automotive air conditioning system consists a refrigeration system, air
circulation and distribution system and a control system. The refrigeration system cool down the air which include many other parts like compressor, condenser etc. The air circulating system circulate this cooled air into the car which include blower, air duct etc. The controlling system used to control the temperature of the car by sensing it and control the refrigerating system.
Principle of Car Air Conditioning System:
The automotive air conditioning system includes the
compressor, condenser, evaporator, receiver-dehydrator and connecting lines
which includes expansion valve, orifice tube, suction throttling valve,
positive operating absolute valve, evaporator pressure regulator valve, thermal
sensor, high pressure cut off switch and cycling compressor switch. In old days
Freon 12 was used as refrigerant but now it is replaced by alternative
refrigerant like R134a. The layout of refrigerating system is as shown in
figure.
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| Layout of Automotive Air Conditioning System |
Working of Car Air Conditioning System:
The working of automotive air condition system is similar to
all other air conditioning system. The refrigerant
vapour from the evaporator is compressed to high pressure by the compressor. The
compressor is driven by the engine through a belt drive. It is connected by a
electromagnetic clutch witch serve engage and disengage the compressor
required. A variable displacement AC compressor is sometime used to match
compressor capacity to varying cooling requirement. Refrigerant pressure and temperature increases
in the compressor and convert it into vapour form. This high pressure and temperature
refrigerant vapour from the compressor then discharge to the condense, which is
a heat exchanger situated in front of vehicle. In the condenser the refrigerant
liberate heat and convert into liquid form. Sometime the ram air is not
sufficient so an extra engine or electric driven fan is used to cool down the refrigerant.
This cooled but high pressure refrigerant allow to pass form dehydrator to
extract any moisture. Dry refrigerant liquid is then made to pass through
expansion valve mounted at the inlet side of the evaporator. The expansion valve
allows the refrigerant liquid to expand to low pressure in the evaporator. The process
of expansion to low pressure makes the refrigerant to evaporate and thereby
cool the evaporator. A sensing devices,
called temperature tube signals the diaphragm in the expansionvalve to vary orifice
size depending upon the refrigerant temperature at the evaporator outlet, thus
achieving automatic temperature control. The evaporator is similar in
construction to the condenser.
The same circulation and distribution system as used for
ventilation and heating system. The air from the blower is forced to flow over
the evaporator coils which remove the latent heat of vaporization, moisture and
impurities form the air. Condenser moisture with the impurities fro the evaporator
drips into a try form where the same are drained out. This system is
microprocessor based and depending upon input signals outside air temperature,
inside air temperature, mode selection and desired temperature setting,
automatically controls the air mixer valve, re-circulation valve etc.
Precaution while using car AC system:
1. Do not use AC fresh air mode open always, since this mode is
for occasional use just to release the air in circulation for a long time.
2. Never operate AC with heater on.
3. Never run AC without refrigerant otherwise compressor may
seize.
4. Do not leave AC joints open which may cause the moisture to
enter the system.
5. Do not charge the refrigerant in the AC system before flushing.
6. Never switch on the AC at high speeds, which may result in
the seizing of compressor.
Tips for maintenance of car AC system:
1. Clean the condenser during normal servicing.
2. Maintain correct refrigerant level. Less refrigerant would
result in less cooling, while excessive would also result lesser cooling and
excessive tripping.
3. Top up the compressor with adequate oil.
4. Clean the evaporator periodically.
5. Maintain proper belt tension. A loose belt will slip whereas
overtight belt would cause noise and premature compressor failure.
Today we have discussed the Air condition system used in car. After reading this article if you have any query, put it into comment box.