The passenger compartment distribution system supplies temperature-controlled air to the passenger compartment and conditioned air (cool air) to the passenger compartment gaspers.

The temperature-controlled air is a mixture of cool air that comes from the air-conditioning system (pack) and hot air that comes from the temperature control system. The quantity of cool air and hot air that makes up the mixture is controlled from the CABIN temperature selector found on the AIR COND/BLEED control panel. The cool air that goes to the passenger compartment gaspers comes from the pack. The passenger-compartment distribution system can also supply ram air. To do so, the RAM AIR push button annunciator (PBA) on the AIR COND/BLEED control panel must be pushed in.

The passenger compartment ducting system is designed for low internal air velocities (below 2,000 ft/min or 609.6 m/min). The low internal air velocities keep pressure losses to a minimum and guarantee minimum noise caused by airflow. The ducting system consists of low-pressure flexible and rigid ducts above and below the aircraft floor.

The ducting system is made up of low pressure flexible and rigid ducts found above and below the aircraft floor. The ducts are attached to one another and to the outlets with tie-down straps or hose clamps. This configuration keeps weight to a minimum and helps in duct installation and removal.

The flexible ducts are made as follows:

• With a layer of silicone-coated fiberglass hose. The hose is made stronger with a coil of metallic or non metallic wire.
• Inlet and outlet ends have two or three layers of silicone made stronger with fiberglass
• Where necessary, the ducts have a layer of thermal insulation

The rigid ducts are made as follows:

• With one or more layers of phenolic resin composite material made stronger with fiberglass. The ducts are locally made stronger with more layers of material at the pneumatic and structural connections.
  
  
• With an internal electrically conductive layer
• Where necessary, the ducts have a layer of thermal insulation

Electrical bonding with the aircraft structure and the temperature sensor is done through fittings, lugs, studs, or check valves that are electrically bonded to the conductive layer of the rigid ducts.

Note:
There is one temperature sensor installed in the passenger-compartment distribution system. It is identified as the cabin duct temperature-sensor. The cabin duct temperature-sensor is found on the rigid tee duct and it is a component of the temperature control and indication system.

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The mix manifold connects the bulkhead check valve (BCKV) to the flight compartment and to the passenger-compartment distribution system. It is found below the floor, forward of the aft pressure bulkhead, near FS669.76.

Note:
The BCKV is a component of the flight compartment distribution system.

The mix manifold has seven openings. They are as follows:

• An air conditioning inlet port that lets cool air from the pack come into the mix manifold.
• An upper passenger-compartment distribution outlet port used for the supply of temperature controlled air, at head level, in the passenger compartment. Downstream from the upper passenger-compartment distribution outlet port, in the cabin trim injector, the cool air that comes out of the port is mixed with hot air that comes from the temperature control system to make temperature controlled air.

Note:
The cabin trim injector is a component of the temperature control and indication system.

• A lower passenger-compartment distribution outlet port and a trim air inlet. Hot air that comes from the temperature control system through the trim air inlet is mixed with cool air from the pack to make temperature controlled air. This temperature controlled air is supplied to the passenger compartment at foot level through the lower passenger-compartment distribution outlet port.
  
  
• A flight-compartment distribution outlet port used for the supply of temperature controlled air in the flight compartment. Downstream from the flight-compartment distribution outlet port, in the flight-compartment feed duct, the cool air that comes out of the port is mixed with hot air that comes from the temperature control system to make temperature controlled air.

Note:
The flight-compartment feed duct is a component of the temperature control and indication system.

• A gasper ducts outlet that supplies cool air to the flight compartment and to the passenger compartment.
• A drain tube to remove water caused by condensation. Condensation can occur when the hot air that comes from the temperature control system meets the cool air that comes from the pack.

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The passenger-compartment gasper ducts supply cool air that comes from the pack to the passenger compartment. The cool air comes from the mix manifold, upstream of the inlets that let hot air from the temperature control system go into the mix manifold.

Note:
Because it comes from upstream of the hot air inlets, the air that flows through the passenger-compartment gasper ducts is cool air (not temperature controlled air).

The passenger-compartment gasper ducts include the components that follow:

• A lower gasper
• A transition gasper
• A center gasper (right-hand side)
• A center gasper (left-hand side)

Note:
The center gasper (right-hand side) also supplies cool air to the flight-compartment gasper ducts.
The flight-compartment gasper ducts are components of the flight-compartment distribution system.

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The rigid connectors (also known as lower riser connectors) connect the mix manifold to the upper supply ducts. They are found below the floor, forward of the aft pressure bulkhead, near FS669.76.

The rigid connectors are made out of glass and silicone components.

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The upper supply ducts connect the rigid connectors to the upper forward flex ducts. They supply temperature controlled air to the upper left and right side of the passenger compartment.

The upper supply ducts include the components that follow:

• A floor riser interface
• An upper riser
• A transition riser
• An upper corner (right-hand side)
• An upper flexible joint
• An upper corner (left-hand side)

The upper supply ducts are found in the aft baggage compartment. They are installed along the right side of the aircraft fuselage, from the floor to the ceiling, between the wall trim and the aircraft skin.

In the ceiling, the ducting system is divided into two distribution ports that supply the left and the right side of the passenger compartment at head level. In the passenger compartment, distribution of temperature controlled air is done through ducts that are part of the interior furniture or liner.

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Four forward flex ducts are part of the passenger-compartment distribution system. They are as follows:

• Two upper forward flex ducts (left side and right side) that connect the upper supply ducts to the ducts that are part of the interior furniture or liner in the passenger compartment at head level.
  
  
• Two lower forward flex ducts (left side and right side) that connect the lower rigid ducts to the ducts that are part of the interior furniture or liner in the passenger compartment at foot level.

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The rigid tee duct connects the center outlet of the mix manifold to the left and right side lower flexible hoses. It supplies temperature controlled air to the lower left and right side of the passenger compartment.

The rigid tee duct has a boss that hosts the cabin duct temperature-sensor.

The rigid tee duct is found below the floor, at FS653.00.

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The lower flexible hoses (left side and right side) connects the rigid tee duct to the left and right side lower rigid ducts. They are part of the series of ducts that let temperature controlled air move from the mix manifold to the passenger compartment at foot level.

The lower flexible hoses are found below the floor, near FS635.65.

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The lower rigid ducts (left side and right side) connect the lower flexible hoses to the lower forward flex ducts.

The lower rigid ducts are found above and below the aircraft floor, at FS635.65.

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The passenger-compartment distribution system supplies temperature controlled air to the passenger compartment and cool air to the passenger compartment gaspers.

The passenger-compartment distribution system is designed to give maximum passenger compartment comfort. Its configuration gives the most equal air temperature distribution. It also keeps air drafts to a minimum.

Air distribution into the passenger compartment is done through two primary lines that are connected to the mix manifold. The two primary lines supply temperature controlled air at the foot and at the head level of the passenger compartment.

The ducts that are part of the passenger-compartment distribution system have thermal insulation for better system performance.

Note:
Much of the air distribution in the passenger compartment is done through ducts that are part of the interior furniture or liner. The ducts that are part of the interior furniture or liner are not shown in the illustrations found in this section because they are completion items and can be different from one aircraft to another.

For the temperature controlled air that goes to the passenger compartment, the path of the airflow is as follows:

• Cool air from the pack goes to the mix manifold through the pack discharge duct and the BCKV.

Note:
The pack discharge duct is a component of the air conditioning system.

• In the mix manifold, the cool air that comes from the pack mixes with the hot air that comes from the temperature control system. That mixture gives temperature controlled air.
  
  
• The quantity of cool air and hot air that makes up the mixture of temperature controlled air is controlled from the CABIN temperature selector found on the AIR COND/BLEED control panel.
  
  
• The temperature controlled air then goes to the passenger compartment, at head and foot level, through a series of ducts.
• The temperature controlled air comes out of the ducts through calibrated exhaust grilles attached at the open ends of the ducts.

For the cool air that goes to the passenger compartment gaspers, the path of the airflow is as follows:

• Cool air from the pack goes to the mix manifold through the pack discharge duct and the BCKV.
• In the mix manifold, cool air is then drawn off immediately upstream of the openings that let the hot air from the temperature control system enter the mix manifold. That cool air (drawn off of the mix manifold) then goes to the passenger-compartment gasper ducts.
  
  
• The cool air that flows through the passenger-compartment gasper ducts is then released through the gasper outlets.

The passenger-compartment distribution system can also supply ram air. To do so, the RAM AIR PBA on the AIR COND/BLEED control panel must be pushed in. When this is done, the ram air valve opens and lets ram air flow into the pack discharge duct. From the pack discharge duct, ram air then goes to the mix manifold through the BCKV. From the mix manifold, the ram air goes to the passenger compartment through the usual passenger-compartment distribution system.

The temperature of the air that flows through the aft fuselage passenger-compartment ducts is sensed by the cabin duct temperature-sensor. The data from the sensor goes to integrated air system (IAS) controller No. 2.

Note:
IAS controllers No. 2 is a component of the cabin-pressure control system.

IAS controller No. 2 monitors the temperature of the air that flows through the passenger compartment ducts for a possible overheat fault condition.

Displays

The AIR COND TEMP HIGH caution message shows when an excessive air temperature has been sensed in the flight compartment air distribution duct.

The TRIM AIR FAIL caution message shows when a hot air regulating valve has malfunctioned or the flight-compartment duct temperature-sensor is out of range or has sent no data.

The EICAS messages that follows are related to the flight compartment distribution system.

EICAS MESSAGE	LEVEL (COLOR)
AIR COND TEMP HIGH	CAUTION (amber)
TRIM AIR FAIL	CAUTION (amber)

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The continuous built-in tests (BIT) that follow are related to the flight-compartment distribution system:

• When the temperature of the air that flows through the flight compartment ducts becomes higher than 185 °F (85 °C) for more than 30 seconds or higher than 212 °F (100 °C) for more than 10 seconds, an AIR COND TEMP HIGH caution message is shown on the EICAS.

Note:
When the AIR COND TEMP HIGH caution message is shown on the EICAS, the AIR SOURCE rotary switch on the AIR COND/BLEED control panel should be set to PACK ONLY.

• When the temperature acquisition range of the flight-compartment duct temperature-sensor is sensed to be out of range, −55 to +200 °F (−48.33 to 93.33 °C), a TRIM AIR FAIL caution message is shown on the EICAS. Confirmation time for the fault condition is 5 seconds.

Note:
When the TRIM AIR FAIL caution message is shown on the EICAS, the AIR SOURCE rotary switch on the AIR COND/BLEED control panel should be set to PACK ONLY or OFF position.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
-	MIX MANIFOLD	ZONE(S) 241/242	21-22-01
-	PASSENGER COMPARTMENT GASPER  DUCTS	ZONE(S) 241/242	21-22-05
-	RIGID CONNECTORS	ZONE(S) 241/242	21-22-07
-	UPPER SUPPLY DUCTS	ZONE(S) 241/242	21-22-09
-	FORWARD FLEX DUCTS	ZONE(S) 241/242	21-22-11
-	RIGID TEE DUCT	ZONE(S) 241/242	21-22-13
-	LOWER FLEXIBLE HOSE	ZONE(S) 241/242	21-22-15
-	LOWER RIGID DUCTS	ZONE(S) 241/242	21-22-17

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