2. Introduction
• A liquid like water or alcohol absorbs the heat in its vicinity as it evaporates.
• When alcohol is put on your skin, you feel chilly.
• This happens because, when the alcohol evaporates, it removes heat from
your skin.
• On the air conditioner cycle, by using the above principle and refrigerant which
is easier to evaporate than alcohol, takes place.
• An application of this principle is refrigeration.
• The higher the vaporizing capacity, the larger the heat absorbing power and
the higher the refrigerating capacity.
3. Function
• The function of air conditioner is to maintain
the life environment in a comfortable
condition. Therefore, complete air
conditioning involves:
i. Temperature control
ii. Air circulation control
iii. Humidity control
iv. Air purification
4. The air conditioner for an automobile generally
consists of a:
i. heating unit
ii. cooling unit
iii. moisture remover
iv. ventilator
5. Basic Cooling System
Refrigeration System
• A device that cools or dehumidifies the air in
the car of fresh outside air drawn into the car
so as to produce comfortable air.
6. Basic Theory of Cooling
• A container provided with a tap is placed
in a well-insulated box.
• A liquid that will vaporize readily at
atmospheric temperature is placed in the
container.
• When the tap is opened, the liquid in the
container will take away the heat
necessary for vaporization from the air
inside the box, turn into a gas and escape
outside.
• At this time, the temperature of the air
inside the box will become lower than that
before the tap was opened.
• We can cool objects in this way
7. Refrigerant
• The refrigerant is used to absorb, transfer and
release heat in the air-conditioning circuit. A
refrigerant must be :
i. Non-flammable
ii. Non-explosive
iii. Non-poisonous
iv. Non-corrosive
v. Odorless
8. R-12
• Substance known as Dichlorodifluoromethane commonly referred to as
Freon or R-12.
• R-12 has the following properties:
i. non-flammable
ii. non-toxic
iii. stable at all temperatures
iv. does not react with aluminium, steel or copper,
v. soluble in mineral oils
vi. low boiling point
vii. vaporizes at minus 30°C
viii. harmful to the environment
9. R-13-a
• It is an HFC or Hydrofluorocarbon.
• R-134a has a boiling point of minus 26.2°C.
• All its other refrigerant characteristics are similar to R-12
EXCEPT
i. Its operating pressures and temperatures in the evaporator
and condenser are slightly higher than for R-12.
ii. R-134a is not soluble in mineral oils (so new compressor
lubricating oils have been developed)
12. High Pressure, Low Pressure
High Temperature Low Temperature
Expansion
Receiver Liquid Evaporator
Liquid valve
refrigerant refrigerant
Liquid Gaseous Low Pressure
refrigerant refrigerant Low Temperature
Gaseous
refrigerant
Condenser Compressor
High Pressure
High Temperature
Refrigeration Cycle
13. Types of Air Conditioner
Car air conditioners are classified according to
the air conditioner unit mounting location
and by the functions of the air conditioner.
14. Mounting Location
Dash Type
The air conditioner unit in this type is normally
installed under the dash panel.
Trunk Type
The air conditioner units is installed in the trunk.
15. Dual Type
The cold air is blown out from the front and rear
of the car interior.
16. Function
Simple Type
This type consists of ventilator connected either
to heater OR to refrigeration system, used
simply for heating or cooling.
17. All Season Type
• This type combines a ventilator with heater
and refrigeration system.
• An all-season air conditioner can be used on a
cold, wet day to dehumidify (dry) the air.
18. Ventilator
A device for leading the fresh
outside air into the car, that also
serves for ventilating the car.
19. Types of Ventilator
Natural flow-through ventilator
Intake of external air into the vehicle’s interior due to
the air pressure generated by the vehicle’s
movement
Forced air ventilator (Boost Ventilator)
An electric fan or similar device is used to force air
through the vehicle
20. Intake vents are located in places where the air pressure is
positive and the exhaust vents are located in places where
the air pressure is negative.
21. Operation of Dampers
Two types of damper operation used are:
1. Lever type
A lever on the control panel is connected to a cable which
moves the damper when the lever is moved.
2. Push-button type
Pressing a push-button on the control panel causes a servo
motor to operate, moving the damper.
22.
23. Blower Operation
• Fresh air or re circulated air drawn in by the
blower.
• In figure below, blower speed control lever on the
control panel can change the blower speed in four
steps, from LO to HI.
• The blower speed is controlled by passing current
through resistors with different resistance values
to change the voltage to the blower motor, thus
changing the blower speed.
26. Magnetic Clutch Control
When the ignition switch is turned ON with blower
switch in any position except OFF, the heater relay goes
ON. If the air conditioner switch is then turned
ON, the magnetic clutch relay is turned ON by the A/C
amplifier. This causes the magnetic clutch to be
engaged. However, the magnetic clutch is disengaged,
and the compressor goes off, under the following
condition.
27. 1. Blower Switch OFF
When the blower switch is turned OFF, the heater relay goes OFF, and power is no longer supply to
the air conditioner.
2. A/C Switch OFF
The main power of the A/C amplifier, which is controls the magnetic clutch relay, is cut off.
3. Evaporator Temperature Too Low
If the temperature at the surface of the evaporator falls to 3°C or below, the A/C amplifier shut off
the magnetic clutch relay
4. Dual Pressure Switch OFF
If the pressure in the high-pressure side of the refrigeration circuit is extremely high or extremely
low, this switch goes OFF. The A/C amplifier senses this, and shuts off the magnetic clutch relay.
5. Compressor Lock-up
If the difference between the compressor speed and the engine speed rises above a certain value,
the A/C amplifier judges that the compressor has locked up, and shuts off the magnetic clutch
relay.
6. Refrigerant Temperature Too High
If the refrigerant temperature in the compressor rises above certain specified level, the temperature
switch goes OFF.
