FLOW CONTROL AND INDICATING - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General
High pressure air is supplied to the air conditioning system from the main pneumatic system. This air goes through two ozone filters 100HM (101HM) and two flow-control valves 11HB (8HB) to two identical independent air conditioning packs 10HM (11HM).
High pressure air is supplied to the air conditioning system from the main pneumatic system. This air goes through two ozone filters 100HM (101HM) and two flow-control units 23HB (24HB) to two identical independent air conditioning packs 10HM (11HM).

** ON A/C NOT FOR ALL

2. Component Location

Flow Control and Indication - Component Location ** ON A/C NOT FOR ALL

FIN	FUNCTIONAL DESIGNATION	PANEL	ZONE	ATA REF
** ON A/C NOT FOR ALL
15HB	RELAY-DISAGREE (L FCV)	95VU	121	21-51-00
16HB	RELAY-ENGINE START	96VU	122	21-51-00
17HB	RELAY-ENGINE START	95VU	121	21-51-00
21HB	RELAY-BACK-UP FLAP DISAGREE	93VU	121	21-51-00
** ON A/C NOT FOR ALL
5HB	CTL SW-AIR COND/PACK FLOW	30VU	211	21-51-00
** ON A/C NOT FOR ALL
5HB	CTL SW-AIR COND/PACK FLOW	30VU	210	21-51-00
** ON A/C ALL
6HB	P/BSW-AIR COND/PACK 2	30VU	210	21-51-00
7HB	P/BSW-AIR COND/PACK 1	30VU	210	21-51-00
** ON A/C NOT FOR ALL
12HB	RELAY-R PACK CLOSE	96VU	122	21-51-00
13HB	RELAY-L PACK CLOSE	95VU	121	21-51-00
14HB	RELAY-DISAGREE (R FCV)	96VU	122	21-51-00
4HB	RELAY-BACK-UP FLAP	103VU	126	21-51-00
** ON A/C NOT FOR ALL
8HB	P2 FLOW CTL VALVE	192KB	192	21-51-51
** ON A/C NOT FOR ALL
8HB	P2 FLOW CTL VALVE		192	21-51-51
** ON A/C NOT FOR ALL
9HB	P2 FLOW SENSOR	192KB	191	21-51-11
** ON A/C NOT FOR ALL
9HB	P2 FLOW SENSOR		191	21-51-11
** ON A/C NOT FOR ALL
10HB	P1 FLOW SENSOR	191KB	191	21-51-11
** ON A/C NOT FOR ALL
10HB	P1 FLOW SENSOR		191	21-51-11
** ON A/C NOT FOR ALL
11HB	P1 FLOW CTL VALVE	191KB	191	21-51-51
** ON A/C NOT FOR ALL
11HB	P1 FLOW CTL VALVE		191	21-51-51
** ON A/C ALL
20HB	MIXER FLAP ACTUATOR	132PW	137	21-51-52
** ON A/C NOT FOR ALL
23HB	FLOW CTL UNIT-PACK 1		191	21-51-51
23HB1	SENSOR-PRESS INLET,PACK 1		191	21-51-13
23HB2	SENSOR-DELTA PRESS,PACK 1		191	21-51-11
24HB	FLOW CTL UNIT-PACK 2		192	21-51-51
24HB1	SENSOR-PRESS INLET,PACK 2		192	21-51-13
24HB2	SENSOR-DELTA PRESS,PACK 2		192	21-51-11
** ON A/C NOT FOR ALL
100HM	P1 OZONE FILTER	191BB	191	21-51-41
** ON A/C NOT FOR ALL
101HM	P2 OZONE FILTER	191BB	192	21-51-41
** ON A/C NOT FOR ALL
100HM	P1 OZONE FILTER		191	21-51-41
101HM	P2 OZONE FILTER		191	21-51-41
** ON A/C NOT FOR ALL
101HM	P2 OZONE FILTER	191BB	191	21-51-41

** ON A/C NOT FOR ALL

3. System Description

Air Supply Regulation ** ON A/C NOT FOR ALL

A. Flow Control Valve / Flow Control Unit
The flow control valves 11HB (8HB) are installed upstream of the air conditioning packs 10HM (11HM). The flow control valves control the quantity of air supplied from the pneumatic system to the air conditioning packs.
They control the airflow fully pneumatically depending on the flow demand and the bleed pressure.
The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
The percentage of airflow through the flow control valves is selected by the PACK FLOW selector 5HB.
The PACK FLOW selector, which is located on the AIR COND panel 30VU, has three positions:

the NORM position, which sets the flow control valve to 100% of the normal airflow,
the LO position, which sets the flow control valve to 80% of the normal airflow.

NOTE: The LO position can be selected for fuel economy purpose.
This position must only be selected when there is a reduced number of passengers in the cabin,

the HI position, which sets the flow control valve to 120% of the normal airflow.

NOTE: This position is selected in abnormal hot ambient conditions or to clear smoke.

The PACK FLOW selector transmits the selected position to the Zone Controller (ZC). The ZC calculates the necessary flow demand and transmits the data to the pack controllers. They set the flow control valves in the necessary reference position.
The PACK 1 and/or the PACK 2 pushbutton switches control the related pack flow control valve to the open or closed position.
The flow control valves close automatically if:

there is an engine start,
there is an ENGINE FIRE pushbutton switch released,
there is a compressor overheat,
there is low bleed pressure,
the DITCHING pushbutton switch 13HL is in the on position,
the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

The flow control valves 11HB (8HB) are installed upstream of the air conditioning packs 10HM (11HM). The flow control valves control the quantity of air supplied from the pneumatic system to the air conditioning packs.
They control the airflow fully pneumatically depending on the flow demand and the bleed pressure.
The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
The percentage of airflow from the flow control valves is selected by the ECON FLOW pushbutton switch 5HB.
The ECON FLOW pushbutton switch, which is located on the AIR COND panel 30VU, has two positions:

the 'off' position, which sets the flow control valve to 100% of the normal airflow,
the ON position, which sets the flow control valve to 80% of the normal airflow.

NOTE: The ON position can be selected for fuel economy purpose.
This position must only be selected when there is a reduced number of passengers in the cabin.

The ECON FLOW pushbutton switch transmits the selected switch position to the Zone Controller (ZC). The ZC calculates the necessary flow demand and transmits the data to the pack controllers. They set the flow control valves in the necessary reference position.
The PACK 1 and/or the PACK 2 pushbutton switches control the related pack flow control valve to the open or closed position.
The flow control valves close automatically if:

there is an engine start,
there is an ENGINE FIRE pushbutton switch released,
there is a compressor overheat,
there is low bleed pressure,
the DITCHING pushbutton switch 13HL is in the on position,
the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

The flow control units 23HB (24HB) are installed upstream of the air conditioning packs 10HM (11HM). The flow control valves of the flow control units control the quantity of air supplied from the pneumatic system to the air conditioning packs.
They control the airflow fully pneumatically depending on the flow demand and the bleed pressure.
The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
The percentage of airflow from the flow control valves is selected by the ECON FLOW pushbutton switch 5HB.
The ECON FLOW pushbutton switch, which is located on the AIR COND panel 30VU, has two positions:

the 'off' position, which sets the flow control valve to 100% of the normal airflow,
the ON position, which sets the flow control valve to 80% of the normal airflow.

NOTE: The ON position can be selected for fuel economy purpose.
This position must only be selected when there is a reduced number of passengers in the cabin.

The ECON FLOW pushbutton switch transmits the selected switch position
to the ACSC 1 (Air Conditioning System Controller) and via ARINC interface to the ACSC 2. The ACSC calculates the necessary flow demand. Both ACSC set the flow control valves in the necessary reference position.
The PACK 1 and/or the PACK 2 pushbutton switches control the related pack flow control valve to the open or closed position.
The flow control valves close automatically if:

there is an engine start,
there is an ENGINE FIRE pushbutton switch released,
there is a compressor overheat,
there is low bleed pressure,
the DITCHING pushbutton switch 13HL is in the on position,
the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

The flow control units 23HB (24HB) are installed upstream of the air conditioning packs 10HM (11HM). The flow control valves of the flow control units control the quantity of air supplied from the pneumatic system to the air conditioning packs.
They control the airflow fully pneumatically depending on the flow demand and the bleed pressure.
The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
The percentage of airflow from the flow control valves is selected by the FLOW selector pushbutton switch 5HB.
The FLOW selector pushbutton switch, which is located on the AIR COND panel 30VU, has three positions:

the NORM position, which sets the flow control valve to 100% of the normal airflow (in flight),
the NORM position, which sets the flow control valve to 90% of the normal airflow (on ground with the packs supplied by engine bleed),
the LO position, which sets the flow control valve to 80% of the normal airflow.

NOTE: The LO position can be selected for fuel economy purpose.
This position must only be selected when there is a reduced number of passengers in the cabin,

the HI position, which sets the flow control valve to 120% of the normal airflow.

NOTE: This position is selected in abnormal hot ambient conditions or to clear smoke.

The FLOW selector transmits the selected switch position to the ACSC 1 (Air Conditioning System Controller) and via ARINC interface to the ACSC 2. The ACSC calculates the necessary flow demand. Both ACSC set the flow control valves in the necessary reference position.
The PACK 1 and/or the PACK 2 pushbutton switches control the related pack flow control valve to the open or closed position.
The ACSC closes the associated flow control valves automatically if:

there is an engine start,
there is an ENGINE FIRE pushbutton switch released,
there is a compressor overheat,
there is low bleed pressure,
the DITCHING pushbutton switch 13HL is in the on position,
the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

NOTE: The ACSC does not check the Ground/Flight signal in addition.

The flow control units 23HB (24HB) are installed upstream of the air conditioning packs 10HM (11HM). The flow control valves of the flow control units control the quantity of air supplied from the pneumatic system to the air conditioning packs.
They control the airflow fully pneumatically depending on the flow demand and the bleed pressure.
The airflow through the flow control valves is selected by the PACK 1 and/or the PACK 2 pushbutton switches.
The percentage of airflow from the flow control valves is selected by the FLOW selector pushbutton switch 5HB.
The FLOW selector pushbutton switch, which is located on the AIR COND panel 30VU, has three positions:

the NORM position, which sets the flow control valve to 100% of the normal airflow,
the LO position, which sets the flow control valve to 80% of the normal airflow.

NOTE: The LO position can be selected for fuel economy purpose.
This position must only be selected when there is a reduced number of passengers in the cabin,

the HI position, which sets the flow control valve to 120% of the normal airflow.

NOTE: This position is selected in abnormal hot ambient conditions or to clear smoke.

there is an engine start,
there is an ENGINE FIRE pushbutton switch released,
there is a compressor overheat,
there is low bleed pressure,
the DITCHING pushbutton switch 13HL is in the on position,
the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.

NOTE: The ACSC does not check the Ground/Flight signal in addition.

B. Pressure Sensors (Flow Sensors)
The pressure sensors 10HB (9HB) measure the difference between a flow control valve reference pressure and the ambient pressure. They transmit signals to the two pack controllers 7HH (27HH). The pack controllers use these signals for calculation of the pack flow.
The differential pressure sensors 23HB2 (24HB2) measure the pressure difference of the flow at the venturi body.
The pack inlet pressure sensors 23HB1 (24HB1) measure the pressure upstream of the venturi.

C. Ozone Filters
The ozone filters 100HM (101HM) are installed upstream of the flow control valves. They catalytically remove the ozone from the hot bleed air before it flows to the air conditioning packs or the trim system.
The ozone filters 100HM (101HM) are installed upstream of the flow control valves. They catalytically remove the ozone from the hot bleed air before it flows to the air conditioning packs or the trim system.

D. Mixer Flap Actuator
The mixer flap actuator 20HB operates a flap in the cockpit supply port of the mixer. The flap connects the cockpit supply duct to the pack 1 mixer chamber, when both packs are in operation. When pack 1 is switched off, the flap changes the position and connects the cockpit supply duct to the pack 2 mixer chamber. This function makes sure of:

a good flow separation during pack 2 operation,
the supply of a sufficient fresh air quantity to the cockpit with pack 1 off.

When the flap in the mixer unit enters the airflow it causes a small airflow diversion into the cockpit duct. This results in an adequate supply of conditioned air to the cockpit.

** ON A/C NOT FOR ALL

4. Power Supply

Flow Control and Indication - Electrical Schematic ** ON A/C NOT FOR ALL

Mixer Flap Actuator - Schematic ** ON A/C NOT FOR ALL

** ON A/C NOT FOR ALL

5. Component Description

A. Flow Control Valve / Flow Control Unit FIN: 11-HB FIN: 8-HB FIN: 23-HB FIN: 24-HB

Flow Control Valve - General View ** ON A/C NOT FOR ALL

Flow Control Unit - General View ** ON A/C NOT FOR ALL

Flow Control Valve - Schematic ** ON A/C NOT FOR ALL

Flow Control Unit - Schematic ** ON A/C NOT FOR ALL

The flow control valves 11HB (8HB) are installed upstream of the air conditioning packs 10HM (11HM). These valves are of the venturi type with a nominal 4 in. (101.5998 mm) diameter. Both have a built-in butterfly valve that controls the flow and can also perform a shut-off function.
The flow control valve has three main assemblies:

the valve body with its butterfly valve,
the pneumatic actuator,
the air pressure regulator.

A pneumatic actuator with a flexible diaphragm (1) controls the butterfly valve. A return spring (2) closes the valve when there is no pressure supply.

The air pressure regulator has:

an air flow sensoring system,
an electro-pneumatic adjustment system,
an electrical venting system.

The flow sensoring system has a pressure sensor which measures the differential pressure in the venturi-shaped valve body. The pressure sensor transfers the pressure into an electrical signal. It amplifies this signal and sends it to the pack controller 7HH (27HH) which calculates the actual air flow.
The pack controller compares the air-flow with the pre-set value from the cockpit, and then calculates if the butterfly position must be changed.

One part of the electro-pneumatic regulator is a pressure reducer. If the pressure after the orifice G2 increases, the spring-loaded pressure reducer closes. This decreases the pressure in the pressure line and the reducer opens again. This protects the valve from damage caused by sudden pressure changes or too high an inlet pressure.
Another part of the electro-pneumatic regulator is a torque motor which turns a quadrant. If the butterfly valve has to be opened, the torque motor turns the quadrant to a position closer to the opening of the pressure line.
This increases the pressure after the orifice G1 and that pressurizes the pneumatic actuator of the valve and so the butterfly opens.

The electrical venting system includes an electromagnetic clapper. When the clapper is energized, solenoid S1 closes the valve by fully venting the pneumatic actuator chamber. When the solenoid is no longer energized, the pneumatic actuator chamber can be pressurized.

A pin situated on the butterfly axis actuates a microswitch, which supplies electrical power to indicate the fully-closed position of the valve.

The flow control valve has a safety feature which prevents a pack overheat:
A pneumatic temperature sensor at the compressor outlet of the air cycle machine is connected to the pneumatic actuator. If the air temperature at the compressor outlet is too high, the pressure line in the temperature sensor opens and the pressurized air in the actuator vents through the now open temperature sensor. This reduces the pressure in the actuator and as an effect of this, the valve closes. The valve will open again if the compressor outlet temperature decreases.
Another control feature is the downstream pressure regulator. If the pressure after the flow control valve is to high, a clapper opens and the pressure vents from the actuator. This closes the valve and the pressure after the valve decreases.
The flow control valve can be closed manually with the use of a special vent screw. If you loosen the screw, the actuator looses pressure, the valve closes and then you use the same screw to fix the valve in the closed position.
The flow control unit 23HB (24HB) is installed in the bleed-air supply line, upstream of the air conditioning pack. The flow control valve of the flow control unit is an electro-pneumatic butterfly valve with the main function:

Control of the mass flow of the bleed-air supply to the pack
Isolation of the pack from the bleed-air supply by crew selection, engine fire, ditching or engine start.
ACM overheat and low pressure start up protection, controlled by the Air Conditioning System Controller (ACSC).

The ACSC1 controls the FCV for pack 1 and ACSC2 controls the FCV for pack 2. Each ACSC uses a close loop electronic control circuit to adjust the butterfly position and the necessary pack inlet flow.

The flow control valve with diameter 4 in. (101.60 mm) has the main components:

an inclined axis valve housing with venturi,
a three chamber pneumatic actuator,
a torque-motor electrical adjustment,
a duplex position sensor (Hall-sensor)
a Differential Pressure Sensor (DPS),
a Pack Inlet Pressure Sensor (PIPS),
a downstream pressure limiter,
an on/off solenoid valve,
a mode selection solenoid valve.

Actuator
The FCV has a spring loaded actuator, which moves the butterfly valve. The supply pressure to operate the pneumatic actuator is tapped from the valve housing. It goes through the flange-assembly and a drilled passage to the inlet chamber of the pneumatic actuator.

Position Sensor
The duplex "Hall" uses two magnetic position sensors to indicate to the
ACSC if the FCV is:

Fully closed (FC)
Not fully closed (NFC)

The FCV operates in the Main, electrical mode and the Back-up, pneumatic mode.
In the main mode, the flow of the FCV is determined through these conditions:

Different flow demands for correct cabin pressure,
Control priorities (take-off, landing, pack start),
Failures and pack overheat conditions.

In back-up mode, the downstream pressure limiter controls the flow of the FCV.
During pack start on ground, the on/off solenoid-valve is energized and the mode selection solenoid-valve is energized for 5 seconds. That means that the FCV operates in back-up mode for 5 seconds. During this time the ACSC monitors the valve function and position indication for failures. After 5 seconds, the FCV changes to main electrical control mode.
During pack start in flight, the on/off solenoid-valve is energized and the mode selection solenoid-valve is de-energized. The FCV operates immediately in main mode.

Main Mode Operation
With the on/off solenoid-valve energized and the mode selection solenoid-valve de-energized, the actuator pressure and the flap position is related to the pressure leakage at the torque motor. The torque motor is driven directly by the ACSC.
The air-flow through the venturi causes a pressure difference. The DPS measures the difference and sends the signal to the ACSC.
The ACSC uses information from the two pressure sensors, along with aircraft cabin altitude and bleed air temperature to calculate the actual flow through the FCV.
The ACSC compares the actual flow to the flow demand. If there is a difference, the ASCS drives the torque motor and adjusts the pressure in the actuator chamber. The pressure in the actuator chamber moves the shaft up and down against the spring force in the ambient chamber and the pressure in inlet chamber. The shaft moves and turns the lever together with the valve flap to get the required air-flow.

Back-up Mode Operation
With the mode-selection solenoid-valve energized, the actuator pressure and thus the valve flap position is related to the pressure leakage at the downstream pressure limiter.
In back-up mode the supply pressure, which operates the pneumatic actuator, goes through the flange-assembly and a drilled passage to the inlet chamber of the pneumatic actuator.
The pressure goes from the inlet chamber to the mode solenoid-valve and stops at the energized on/off solenoid.
From the mode selection solenoid-valve goes the pressure to the pressure limiter.
The downstream pressure goes through a drilled passage in the valve housing to the mode selection solenoid-valve and from there to the pressure limiter into the spring chamber. This pressure, together with the spring force, opens or closed the poppet valve and controls the pressure in the actuator chamber.
The changed pressure in the actuator chamber moves the shaft up and down against the spring force in the ambient chamber and the pressure in the inlet chamber. The shaft moves and turns the lever together with the valve flap to get the required air-flow.

Overheat Protection
The ACSC monitors the compressor discharge temperature for overheat conditions. If the FCV operates in the main mode, a temperature of more than 215 DEG.C (419.00 DEG.F) at the compressor discharge sensor, will cause the ACSC to reduce the electrical supply of the torque motor. This reduces the vented air at the torque motor and therefore the pressure in the actuator chamber will decrease. This causes the spring in the ambient chamber to expand and moves the shaft. The shaft moves up and turns the lever together with the valve flap to decrease the air-flow to the pack.
The reduced air-flow decreases the ACM speed and thus the compressor discharge temperature.
A temperature of more than 260 DEG.C (500.00 DEG.F) at the compressor discharge sensor will cause a pack overheat warning. If the AC is on ground, the ACSC removes the electrical supply to the on/off solenoid valve. The FCV closes and stops the air-flow to the pack.

B. Pressure Sensor

Pressure Sensor ** ON A/C NOT FOR ALL

The pressure sensors 10HB (9HB) measure the difference between the pressure at the inlet of the flow-control-valve venturi and the pressure at its narrowest diameter. This differential pressure is equivalent to the airflow through each flow control valve 8HB (11HB).
The sensors measure pressure with a pressure sensitive diaphragm which transfers pressure into an electrical signal. This signal is amplified and then sent to the pack controller.
Each sensor consists of:

a high-precision pressure transducer,
a measurement amplifier,
an electrical connector.

Differential Pressure Sensor (DPS), Pack Inlet Pressure Sensor (PIPS).
The differential pressure sensors 23HB2 (24HB2) measure the pressure difference of the flow at the venturi body. The pressure difference is used for flow calculation.
The pack inlet pressure sensors 23HB1 (24HB1) measure the pressure upstream of the venturi.
The sensors transfers pressure into an electrical signal. This signal is amplified and then sent to the Air Conditioning System Controller.
Each sensor consists of:

a high-precision pressure transducer,
a measurement amplifier,
an electrical connector.

C. Mixer Flap Actuator
The mixer flap actuator 20HB operates a flap in the cockpit supply port of the mixer.
A thermally protected 28 V DC motor drives the back-up flap through a reduction gearbox. Microswitches inside the mixer flap actuator 20HB prevent override of the flap at each end of its travel. A manual override lever and position indicator (on top of the actuator) make it possible to operate the flap manually.

D. Ozone Filter

Ozone Filter

The ozone filters 100HM (101HM) are installed upstream of the flow control valves 8HB (11HB). The ozone filters consist of a stainless steel housing with a honeycomb core. This core contains a precious metal for the catalytic removal of ozone from the hot bleed air supplied to the packs 10HM (11HM) and the trim system. The ceramic core is fixed in the housing with a knitted, corrugated wire mesh which prevents damage from vibrations or shocks.
The ozone filters 100HM (101HM) are installed upstream of the flow control units 23HB (24HB). The ozone filters consist of a stainless steel housing with a honeycomb core. This core contains a precious metal for the catalytic removal of ozone from the hot bleed air supplied to the packs 10HM (11HM) and the trim system. The ceramic core is fixed in the housing with a knitted, corrugated wire mesh which prevents damage from vibrations or shocks.
The ozone filters 100HM (101HM) are installed upstream of the flow control units 23HB (24HB). The ozone filters consist of a stainless steel housing with a honeycomb core. This core contains a precious metal for the catalytic removal of ozone and Volatile Organic Components (VOC) from the hot bleed air supplied to the packs 10HM (11HM) and the trim system. The ceramic core is fixed in the housing with a knitted, corrugated wire mesh which prevents damage from vibrations or shocks.

** ON A/C NOT FOR ALL

6. Operation/Control and Indicating

Air Supply Regulation ** ON A/C NOT FOR ALL

Flow of Air into Pressurized Fuselage ** ON A/C NOT FOR ALL

APU Flow to Pressurized Fuselage

Flow Control and Indication - Electrical Schematic ** ON A/C NOT FOR ALL

Mixer Flap Actuator - Schematic ** ON A/C NOT FOR ALL

A. Flow Control Valve

(1) General Information
Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

(2) Normal Operation (packs running on engine bleed supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI position.

This position selects the flow control reference in the zone controller 8HK to 80%, 100% or 120%.
The zone controller calculates the necessary flow and transmits this value to the pack controllers 7HH (27HH).
The pack controllers then set the flow control valves 11HB (8HB) to the demanded position.

When the PACK FLOW selector is set to the LO position, and the temperature demand cannot be reached, the zone controller will increase the normal airflow of the flow control valve from 80% to 100%.

(3) APU in Operation (packs running on APU bleed air supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The zone controller 8HK receives the APU bleed valve open signal.
The flow control reference in the zone controller is set to 120% and the flow control valves are commanded to the fully open position.

(4) Single Pack Operation (pack running on engine or APU bleed air supply)
When a pack pushbutton switch is pushed in (the OFF legend goes off) the respective flow control valve opens.
Irrespective of which position the PACK FLOW selector is set to, the zone controller and the pack controller will modulate the pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.

(5) Operation with Failures

(a) Single Pack Failure
When the PACK FLOW selector is set to the NORM or LO position and there is a failure in one pack, the zone controller and the pack controllers modulate the other pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.

(b) Engine Fire
If there is an engine fire, and you push the applicable FIRE pushbutton switch, the respective flow control valve closes. This stops the hot bleed air flow in order to prevent damage to the components of the air conditioning system and to prevent entry of smoke into the cabin.

(c) Ditching
In case of landing on water the DITCHING pushbutton switch must be pushed. This closes the flow control valves which prevents the entry of water into the cabin through the air conditioning system.

(d) Air-Cycle Machine Compressor Overheat
If the compressor of an air-cycle machine overheats, the applicable flow control valve starts to close.
When the compressor temperature reaches 260 deg.C (500.00 deg.F) the flow control valve will fully close.

(e) Pack Shut-down in the Engine-Start Sequence
In the engine-start sequence (the EIU gives an engine rpm-signal of N2 below idle), normally both air-packs close.
To prevent the complete pack shut-down in flight because of a wrong EIU-signal, the crossbleed valve indication relay 7HV monitors the position of the Cross Bleed Valve (CBV) 6HV:

If the CBV is in the closed position, only one pack instead of both closes.

(6) General Information
Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

(7) Normal Operation (packs running on engine bleed supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) then the flow control valves open.
The crew selects the ECON FLOW pushbutton switch 5HB to the ON or off position.

This switch position selects the flow control reference in the zone controller 8HK to 80% or 100%.
The zone controller calculates the necessary flow and transmits this value to the pack controllers 7HH (27HH).
The pack controllers then set the flow control valves 11HB (8HB) to the demanded control position.

When the ECON FLOW pushbutton switch is set to ON and the temperature demand cannot be reached, the zone controller will increase the normal airflow of the flow control valve from 80% to 100%.

(8) APU in operation (packs running on APU bleed air supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) then the flow control valves open.
The zone controller 8HK receives the APU bleed valve open signal.
The flow control reference in the zone controller is set to 120% and the flow control valves are commanded to the fully open position.

(9) Single Pack Operation (pack running on engine or APU bleed air supply)
When a pack pushbutton switch is pushed in (the OFF legend goes off) the respective flow control valve opens.
Irrespective of which position the ECON FLOW pushbutton switch is set to, the zone controller and the pack controller will modulate the pack to the 120% mode. Thus the flow control valve is commanded to the fully open position.

(10) Operation with Failures

(a) Single Pack Failure
When the ECON FLOW pushbutton switch is in the ON (80%) or 'off' (100%) mode, and there is a failure in one pack, then the zone controller and the pack controllers modulate the other pack to the 120% mode. Thus the flow control valve is commanded to the fully open position.

(b) Engine Fire
If there is an engine fire and you push the applicable FIRE pushbutton switch the respective flow control valve closes. This stops the hot bleed air flow in order to prevent damage to the components in the air conditioning system and to prevent entry of smoke into the cabin.

If the CBV is in the closed position, only one pack instead of both closes.

(11) General Information
Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

(12) Normal Operation (packs running on engine bleed supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI position.

This position selects the flow control reference in the ACSC 47HH (57HH) to 80%, 100% or 120%.
The ACSC calculates the necessary flow and then sets the flow control valves 23HB (24HB) to the demanded position.

When the PACK FLOW selector is set to the LO position, and the temperature demand cannot be reached, the ACSC will increase the normal airflow of the flow control valve from 80% to 100%.

(13) APU in Operation (packs running on APU bleed air supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The ACSC 47HH (57HH) receives the APU bleed valve open signal.
The flow control reference in the ACSC is set to 120% and the flow control valves are commanded to the fully open position.

(14) Single Pack Operation (pack running on engine or APU bleed air supply)
When a pack pushbutton switch is pushed in (the OFF legend goes off) the respective flow control valve opens.
Irrespective of which position the PACK FLOW selector is set to, the ACSC will modulate the pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.

(15) Operation with Failures

(a) Single Pack Failure
When the PACK FLOW selector is set to the NORM or LO position and there is a failure in one pack, the ACSC modulates the other pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.

(d) Air-Cycle Machine Compressor Overheat
If the compressor of an air-cycle machine exceeds 215 deg.C (419.00 deg.F), the ACSC and flow control valve will start to reduce the pack flow independent of the flow demand till the minimum flow demand is reached.
When the compressor temperature reaches 260 deg.C (500.00 deg.F) (overheats) on ground, the ACSC will shut off the pack (flow control valve is closed).

(e) Pack Shut-down in the Engine-Start Sequence
In the engine-start sequence (the EIU gives an engine rpm-signal of N2 below idle), normally both air-packs close.
To prevent the complete pack shut-down in flight because of a wrong EIU-signal, the ACSC monitors the position of the Cross Bleed Valve (CBV) 6HV:

If the CBV is in the closed position, only one pack instead of both closes.

(16) General Information
Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

(17) Normal Operation (packs running on engine bleed supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) then the flow control valves open.
The crew selects the ECON FLOW pushbutton switch 5HB to the ON or off position.

This switch position selects the flow control reference in the ACSC 47HH (57HH) to 80% or 100%.
The ACSC calculates the necessary flow and then sets the flow control valves 23HB (24HB) to the demanded position.

When the ECON FLOW pushbutton switch is set to ON and the temperature demand cannot be reached, the ACSC will increase the normal airflow of the flow control valve from 80% to 100%.

(18) APU in operation (packs running on APU bleed air supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) then the flow control valves open.
The ACSC 47HH (57HH) receives the APU bleed valve open signal.
The flow control reference in the ACSC is set to 120% and the flow control valves are commanded to the fully open position.

(19) Single Pack Operation (pack running on engine or APU bleed air supply)
When a pack pushbutton switch is pushed in (the OFF legend goes off) the respective flow control valve opens.
Irrespective of which position the ECON FLOW pushbutton switch is set to, the ACSC will modulate the pack to the 120% mode. Thus the flow control valve is commanded to the fully open position.

(20) Operation with Failures

(a) Single Pack Failure
When the ECON FLOW pushbutton switch is in the ON (80%) or 'off' (100%) mode, and there is a failure in one pack, then the ACSC modulates the other pack to the 120% mode. Thus the flow control valve is commanded to the fully open position.

(e) Pack Shut-down in the Engine-Start Sequence
In the engine-start sequence (the EIU gives an engine rpm-signal of N2 below idle), normally both air-packs close.
To prevent the complete pack shut-down in flight because of a wrong EIU-signal, the ACSC monitors the position of the Cross Bleed Valve (CBV) 6HV:

If the CBV is in the closed position, only one pack instead of both closes.

(21) General Information
Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

(22) Normal Operation (packs running on engine bleed supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI position.

This position selects the flow control reference in the ACSC 47HH (57HH) to 80%, 100% (90% on ground with the packs supplied by engine bleed) or 120%.
The ACSC calculates the necessary flow and then sets the flow control valves 23HB (24HB) to the demanded position.

When the PACK FLOW selector is set to the LO position, and the temperature demand cannot be reached, the ACSC will increase the normal airflow of the flow control valve from 80% to 100% (in flight) and from 80% to 90% (on ground with the packs supplied by engine bleed).

(23) APU in Operation (packs running on APU bleed air supply)
When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the OFF legends go off) the flow control valves open.
The ACSC 47HH (57HH) receives the APU bleed valve open signal.
The flow control reference in the ACSC is set to 120% and the flow control valves are commanded to the fully open position.

(24) Single Pack Operation (pack running on engine or APU bleed air supply)
When a pack pushbutton switch is pushed in (the OFF legend goes off) the respective flow control valve opens.
Irrespective of which position the PACK FLOW selector is set to, the ACSC will modulate the pack to the 120% (HI) mode. Thus the flow control valve is commanded to the fully open position.

(25) Operation with Failures

(e) Pack Shut-down in the Engine-Start Sequence
In the engine-start sequence (the EIU gives an engine rpm-signal of N2 below idle), normally both air-packs close.
To prevent the complete pack shut-down in flight because of a wrong EIU-signal, the ACSC monitors the position of the Cross Bleed Valve (CBV) 6HV:

If the CBV is in the closed position, only one pack instead of both closes.

B. Mixer Flap Actuator

(1) Normal Operation
When the PACK 1 and PACK 2 pushbutton switches or only the PACK 1 pushbutton switch is(are) 'on' the mixer flap actuator 20HB is in the closed position. Thus air is supplied from the pack 1 mixer chamber to the cockpit.
When the PACK 1 pushbutton switch is released (the OFF legend is on) the mixer flap actuator opens and the air is supplied from the pack 2 mixer chamber to the cockpit.

(2) Operation with Failures
If the mixer flap actuator 20HB has a failure, the zone controller 8HK monitors the failure and keeps it in the nonvolatile memory.

(3) Normal Operation
When the PACK 1 and PACK 2 pushbutton switches or only the PACK 1 pushbutton switch is(are) 'on' the mixer flap actuator 20HB is in the closed position. Thus air is supplied from the pack 1 mixer chamber to the cockpit.
When the PACK 1 pushbutton switch is released (the OFF legend is on) the mixer flap actuator opens and the air is supplied from the pack 2 mixer chamber to the cockpit.

(4) Operation with Failures
If the mixer flap actuator 20HB has a failure, the ACSC 2 (57HH) monitors the failure and keeps it in the nonvolatile memory.

C. PACK FLOW Switch
The PACK FLOW selector 5HB is a three position switch and is installed on the AIR COND panel 30VU. You can set the switch to LO, NORM or HI position. This switch selects the amount of airflow through the flow control valves 11HB (8HB).
The usual position is NORM. This gives 100 % of normal airflow to the air conditioning packs.
In position LO the valve selects 80 % of normal airflow.
In position HI the valve selects 120 % of normal airflow.
The ECON FLOW pushbutton switch 5HB has an ON and an off position. It is installed on the AIR COND panel 30VU. This switch selects the amount of airflow through the flow control valves 11HB (8HB).
In normal conditions the pushbutton switch is switched to off. This gives 100 % of normal airflow.
When the ECON FLOW pushbutton switch is switched to ON, the normal airflow to the air conditioning packs is reduced to 80%.
The PACK FLOW selector 5HB is a three position switch and is labeled LO, NORM and HI. It is installed on the AIR COND panel 30VU. This switch selects the amount of airflow through the flow control valves 23HB (24HB).
In normal conditions the selector is selected to NORM. This gives 100 % of normal airflow.
LO selects 80 % of normal airflow to the air conditioning packs and HI selects 120 % of normal airflow.
The ECON FLOW pushbutton switch 5HB has an ON and an off position. It is installed on the AIR COND panel 30VU. This switch selects the amount of airflow through the flow control valves 23HB (24HB).
In normal conditions the pushbutton switch is switched to off. This gives 100 % of normal airflow.
When the ECON FLOW pushbutton switch is switched to ON, the normal airflow to the air conditioning packs is reduced to 80%.
The PACK FLOW selector 5HB is a three position switch and is labeled LO, NORM and HI. It is installed on the AIR COND panel 30VU. This switch selects the amount of airflow through the flow control valves 23HB (24HB).
In normal conditions the selector is selected to NORM. This gives 100 % of normal airflow (in flight) and 90% of normal airflow (on ground with the packs supplied by engine bleed).
LO selects 80 % of normal airflow to the air conditioning packs and HI selects 120 % of normal airflow.

D. Pack 1 (2) Pushbutton Switches
The PACK 1 (2) pushbutton switches 6HB (7HB) are located on the AIR COND panel 30VU.
When a fault occurs the FAULT legend of the respective pack switch shows amber.
When a pack system is not in operation the OFF legend of the respective pack switch shows white.
The different selections of the PACK 1 (2) pushbutton switch are as follows:
The PACK 1 (2) pushbutton switches 6HB (7HB) are located on the AIR COND panel 30VU.
When a fault occurs the FAULT legend of the respective pack switch shows amber.
When a pack system is not in operation the OFF legend of the respective pack switch shows white.
The different selections of the PACK 1 (2) pushbutton switch are as follows:

(1) Switch released:

(a) The OFF legend in the switch shows white,

the respective pack system is not in operation and its flow control valve is closed,
the mixer flap is at position 'C' (connects the cockpit supply duct to the pack 1 mixer chamber), or position 'O' (connects the cockpit supply duct to the pack 2 mixer chamber).
The mixer flap is at position 'O' when only the PACK 1 pushbutton switch is released.

(2) Switch pushed in:

(a) No legend/s shown,

the respective pack system is on and its flow control valve opens automatically.
the mixer flap is at position 'C' or position 'O'.
The mixer flap is at position 'C' when only the PACK 1 pushbutton switch is pushed in or when both the PACK 1 and PACK 2 pushbutton switches are pushed in.

(b) The FAULT legend in the switch shows amber.
This indicates that in the respective pack system:

a compressor temperature of more than 260 deg.C (500.00 deg.F) has occurred or,
a compressor temperature of between 230 deg.C (446.00 deg.F) and 260 deg.C (500.00 deg.F) has occurred four times in one flight or,
a pack discharge temperature of more than 95 deg.C (203.00 deg.F) has occurred.

The switch must be switched off manually.

(3) Switch released:

(a) The OFF legend in the switch shows white,

the respective pack system is not in operation and its flow control valve is closed,
the mixer flap is at position 'C' (connects the cockpit supply duct to the pack 1 mixer chamber), or position 'O' (connects the cockpit supply duct to the pack 2 mixer chamber).
The mixer flap is at position 'O' when only the PACK 1 pushbutton switch is released.

(4) Switch pushed in:

(a) No legend/s shown,

the respective pack system is on and its flow control valve opens automatically.
the mixer flap is at position 'C' or position 'O'.
The mixer flap is at position 'C' when only the PACK 1 pushbutton switch is pushed in or when both the PACK 1 and PACK 2 pushbutton switches are pushed in.

(b) The FAULT legend in the switch shows amber.
This indicates that in the respective pack system:

a compressor temperature of more than 260 deg.C (500.00 deg.F) has occurred or,
a pack discharge temperature of more than 95 deg.C (203.00 deg.F) has occurred.

The switch must be switched off manually.

** ON A/C NOT FOR ALL

7. BITE Test
The pack controllers 7HH (27HH) control the BITE function for the flow control valves (Ref. AMM D/O 21-61-00-00).
The Air Conditioning System Controllers 47HH (57HH) control the BITE function for the flow control valves (Ref. AMM D/O 21-61-00-00).

[Rev.10 from 2021] 2026.04.01 04:54:53 UTC