1. GROUND SERVICING OF VARIOUS SUB SYSTEMS

2. Aircraft air conditioning system
Aircraft-cooling systems, also called air-conditioning systems, are used to reduce the temperature inside an aircraft for crew and passenger comfort
Types
vapor-cycle machine
air-cycle machine

3. vapor-cycle machine
The vapor-cycle machine is a closed system using the evaporation and condensation of Freon to remove heat from the cabin interior.

4. Vapor-Cycle Cooling Systems
The vapor-cycle air-conditioning system is used in reciprocating engine powered aircraft and in smaller turboprop aircraft.
The operation of vapor-cycle machines is controlled by the pilot and may incorporate automatic cutout or interrupt systems.
These cutout and interrupt systems are used to disengage the refrigerant compressor during demand for high engine power output

5. Conti..
A vapor-cycle cooling system using two heat-exchangers to control the temperature of the cockpit and cabin.
The one heat exchanger draws heat from the air and adds it to the closed system. This heat exchanger is called a condenser. The Another heat exchanger taking heat from the closed system, and is called an evaporator.
Instead of water in the heat exchanger, a special fluid called a refrigerant is used. The refrigerant, usually Freon, takes two forms during the cooling process, liquid and gas

7. Conti..
The cooling process starts at the compressor, where the refrigerant is in a gaseous form. The function of the compressor is to push the refrigerant, under pressure, through the entire system.
As the gas enters the condenser, heat is drawn from the refrigerant and passed to the atmosphere. The cooling of the refrigerant causes it to condense into a liquid. Because of the compressor, the liquid is under pressure.

8. Conti..
The pressurized liquid is then metered into tiny droplets by an expansion valve.
The droplets then enter the evaporator, where they draw heat from the air and then change into a gas.
As a result of heat being drawn from the air, the temperature of the air is decreased. It is this cooler air that is introduced to the cabin for cooling

9. Air-Cycle Cooling
Modern large turbine powered aircraft make use of air-cycle machines to adjust the temperature of the air directed into the passenger and crew compartments of these large aircraft.
the cabin can also be heated and pressurized by the use of an air-cycle machine
These large aircraft utilize air-cycle cooling because of its simplicity, freedom from troubles.

10. Conti.. Refrigerant used – Air.
The principle of cooling by means of a gas is simple. When a gas (air) is compressed, it becomes heated, and when the pressure is reduced, the gas becomes cooled.
If a pressure cylinder is connected to an air compressor and compressed air is forced into the cylinder, one can observe that the cylinder becomes warm or even hot, depending upon the level of compression and the rate at which the air is compressed.

11. Conti..
If the cylinder filled with highly compressed air is then allowed to cool to ambient temperature, the pressure in the cylinder will be reduced to a certain degree as the air temperature is reduced.
If a valve is then opened and the air is allowed to escape from the cylinder, the temperature of the escaping air will be much lower than the ambient temperature due to the air expanding as its pressure returns to the ambient value. This cold air can then be used as a cooling agent.
In an air-cycle system, the air is continuously compressed and then cooled by means of heat exchangers through which ram air is passed; then the pressure is reduced by passing the air through an expansion turbine

13. Conti..
The air leaving the expansion turbine is at low pressure and low temperature. The cooled air is directed through ducting with control valves to regulate the amount of cooling air needed to produce the desired cabin temperature.
The turbine-compressor unit by which air is cooled is called an air-cycle machine (ACM).
Hot compressed air from the compressor of one of the turbine engines flows through the primary heat exchanger. The heat exchanger is exposed to ram air, which removes heat from the air.

14. Conti..
The cooled but still compressed air is then ducted to the compressor inlet of the ACM. The compressor further compresses the air and causes it to rise in temperature. This air is directed to the secondary heat exchanger, which, being exposed to ram air, removes heat from the compressed air.
The compressed air is then directed to the expansion turbine. The expansion turbine absorbs energy from the air and utilizes this energy to drive the compressor.
As the air exits the expansion turbine, it enters a large chamber, which allows the air to expand and causes a further reduction in the air temperature.

15. Conti..
Thus the air leaving the turbine is cooled by the loss of heat energy and by the expansion that takes place. The great reduction in temperature causes the moisture in the air to condense, and this moisture is removed by means of a water separator.
The dried, cold air is then routed to ducting to be utilized as required to provide the desired temperature in the cabin.

16. AIR CONDITIONING SYSTEM MAINTENANCE
Procedure depends on the particular aircraft model
Maintenance and manufacturer manual must be referred for correct procedure
It is consists of inspections, servicing, removing, and installing components, performing operational checks, and troubleshooting for the isolation and correction of troubles within the system

17. Inspections
Periodically inspect the system for component security and visible defects.
Particular attention should be paid to the heat exchangers for signs of structural fatigue adjacent to welds
The ducting should be securely attached and adequately supported.
Insulating blankets must be in good repair and secured around the ducting.

18. Servicing
Each refrigeration unit contains Freon for absorbing heat, plus oil mixed with the Freon for lubricating the compressor motor bearings.
insufficient Freon system incapable of absorbing heat.
insufficient oil, the motor bearings will overheat and cause unsatisfactory compressor operation.
System Freon loop contains quantities of both liquid and vapor. So it is unpredictable exactly where in the system the liquid will be at any one instant makes it difficult to check the quantity of Freon in the system.
a standard set of conditions should be obtained when checking the Freon level. These conditions are specified by the manufacturer

19. Conti..
To check the Freon level, it is necessary to operate the refrigeration unit for approximately 5 min to reach a stable condition
If the system uses a sight glass, observe the flow of Freon through the sight glass. A steady flow indicates that a sufficient charge is present If the Freon charge is low, bubbles will appear in the sight glass.
When adding Freon to a system, add as much oil as is felt was lost with the Freon being replaced. It is impossible to determine accurately the amount of oil left in a Freon system after partial or complete loss of the Freon charge

20. Conti..
Usually one-fourth-once of oil is added for each pound of Freon added to the system
The oil used is a special highly refined mineral oil free from wax, water and sulfur. Always use the oil specified in the manufacturer's maintenance manual for a specific system.