-
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,
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 -the applicable PACK 1 or PACK 2 pushbutton switch is in the off position.
 B. Pressure Sensor (Flow Sensor) 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.
 C. 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.
R

R **ON A/C 301-399,
 A. Flow Control Valve 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.
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 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.
 B. Pressure Sensor (Flow Sensor)
 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.
 C. 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. 
R  **ON A/C 401-499, 
R  A. Flow Control Unit 
R  The flow control units 23HB (24HB) are installed upstream of the air 
R  conditioning packs 10HM (11HM). The flow control valves of the flow 
　
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