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.
Function• The function of air conditioner is to maintain the life environment in a comfortable condition. Therefore, complete air conditioning involves:i. Temperature controlii. Air circulation controliii. Humidity controliv. Air purification
The air conditioner for an automobile generallyconsists of a:i. heating unitii. cooling unitiii. moisture removeriv. ventilator
Basic Cooling SystemRefrigeration 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.
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
Refrigerant• The refrigerant is used to absorb, transfer and release heat in the air-conditioning circuit. A refrigerant must be :i. Non-flammableii. Non-explosiveiii. Non-poisonousiv. Non-corrosivev. Odorless
R-12• Substance known as Dichlorodifluoromethane commonly referred to as Freon or R-12.• R-12 has the following properties:i. non-flammableii. non-toxiciii. stable at all temperaturesiv. does not react with aluminium, steel or copper,v. soluble in mineral oilsvi. low boiling pointvii. vaporizes at minus 30°Cviii. harmful to the environment
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 EXCEPTi. 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)
Water cycle, also known as the hydrologic cycle
High Pressure, Low Pressure High Temperature Low Temperature ExpansionReceiver Liquid Evaporator Liquid valve refrigerant refrigerant Liquid Gaseous Low Pressure refrigerant refrigerant Low Temperature Gaseous refrigerant Condenser Compressor High Pressure High Temperature Refrigeration Cycle
Types of Air ConditionerCar air conditioners are classified according tothe air conditioner unit mounting locationand by the functions of the air conditioner.
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.
Dual TypeThe cold air is blown out from the front and rearof the car interior.
FunctionSimple TypeThis type consists of ventilator connected eitherto heater OR to refrigeration system, usedsimply for heating or cooling.
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.
Ventilator A device for leading the freshoutside air into the car, that also serves for ventilating the car.
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
Intake vents are located in places where the air pressure ispositive and the exhaust vents are located in places wherethe air pressure is negative.
Operation of DampersTwo types of damper operation used are:1. Lever typeA lever on the control panel is connected to a cable whichmoves the damper when the lever is moved.2. Push-button typePressing a push-button on the control panel causes a servomotor to operate, moving the damper.
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.
Magnetic Clutch ControlWhen the ignition switch is turned ON with blowerswitch in any position except OFF, the heater relay goesON. If the air conditioner switch is then turnedON, the magnetic clutch relay is turned ON by the A/Camplifier. This causes the magnetic clutch to beengaged. However, the magnetic clutch is disengaged,and the compressor goes off, under the followingcondition.
1. Blower Switch OFFWhen the blower switch is turned OFF, the heater relay goes OFF, and power is no longer supply tothe air conditioner.2. A/C Switch OFFThe main power of the A/C amplifier, which is controls the magnetic clutch relay, is cut off.3. Evaporator Temperature Too LowIf the temperature at the surface of the evaporator falls to 3°C or below, the A/C amplifier shut offthe magnetic clutch relay4. Dual Pressure Switch OFF If the pressure in the high-pressure side of the refrigeration circuit is extremely high or extremelylow, this switch goes OFF. The A/C amplifier senses this, and shuts off the magnetic clutch relay.5. Compressor Lock-upIf 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 clutchrelay.6. Refrigerant Temperature Too HighIf the refrigerant temperature in the compressor rises above certain specified level, the temperatureswitch goes OFF.