Air conditioning Flashcards
What are the temperature controlled zones?
The air is distributed into four independently controlled zones, the cockpit, the forward cabin, the mid cabin and the aft cabin.
Describe the packs and its components
The main components of the air conditioning system are the two independent, automatically controlled packs.
Each pack is comprised of an air cycle machine, a primary heat exchanger and a main heat exchanger.
The heat exchangers use external ram air to cool the hot pneumatic air; the ram air is then exhausted overboard.
Where are the packs located?
The packs are located in the unpressurized belly area, just forward of the main landing gear bay.
How do the heat exchangers work?
The heat exchangers use external ram air to cool the hot pneumatic air; the ram air is then exhausted overboard.
The pack flow control valve will close automatically if:
The pack flow control valve will close automatically if: pneumatic pressure is low, the pack overheats or during the engine start sequence. The valve will also close if the engine fire or ditching pb switches are operated, or if doors are not closed at engines start.
Describe the mixer unit.
The mixer unit mixes temperature regulated air from the packs with re-circulated cabin air drawn in by the cabin fans, which are controlled from the overhead VENTILATION panel.
The mixer unit can also receive conditioned air from an external low pressure air conditioning unit, or ram air from the emergency ram air inlet.
How is temperature regulation achieved?
The conditioned air from the mixer unit is temperature regulated by the hot air valves and trim air valves, which use hot pneumatic air tapped upstream of the packs.
Describe hot air valves.
The hot air valves are pneumatically operated and electrically controlled by the HOT AIR 1(2) pb sw(s) on the overhead AIR panel.
The valves supply the trim air valves with hot pneumatic air which is tapped upstream of the packs.
When will the hot air valves automatically close?
The valves will close automatically if a duct overheats, or in the absence of pneumatic pressure.
Function o hot air cross valve.
A hot air cross valve is fitted between the hot air manifolds; normally closed, it opens automatically if one hot air supply has failed.
Function of trim air valves.
The trim air valves are electrically controlled by the zone controller to add hot pneumatic air from the hot air manifold to the conditioned air of the mixer unit before it enters the cabin, satisfying the demand for individual zone heating.
What controls the temperature and airflow of the air conditioning system?
One zone controller and two pack controllers automatically control the temperature and airflow of the air conditioning system.
The zone and pack controllers are dual channel controllers. Channel 1 normally controls with channel 2 as a backup if channel 1 fails.
Describe the pack controllers.
Each pack has an associated pack controller, which controls the airflow of the pack by modulating the pack flow control valve.
How do the pack controllers control the temperature of the packs?
The pack controller controls the temperature of the pack by modulating the position of the temperature control valve, and the ram air heat exchanger inlet and outlet flaps.
A signal corresponding to the lowest demanded zone temperature goes to the pack controller, which then makes both packs produce the required outlet temperature.
How do the pack controllers help prevent foreign object damage from ingestion by the packs?
The pack controller also closes the ram air heat exchanger inlet and outlet flaps during take-off and landing to prevent foreign object damage from ingestion by the packs.
