ATA 21 - AIR CONDITIONING

• The packs supply dry air to the cabin for air conditioning, ventilation and pressurization.

• ACM (Air Cycle Machine) is the main component in the pack sys.

• During normal operation, the Zone Controller (ZC) calculates the flow mass demand and transmits the data to the Pack Controller (PC) which set the pack flow control valve in the necessary reference position.

• There are two automatic pressurization systems. Each CPC (Cabin Pressure Controller) and its electric motor make up one system. Only one system operates at a time with the other system acting as backup in case of a failure. The system in command will alternate each flight.

• The FCV (Flow Control Valve) is electrically controlled to closed:

1) During engine start

2) if the corresponding engine fire P/B is pushed,

3) If the ditching P/B is set to “ON”,

4) If the corresponding PACK P/B is set to “OFF”

* On the Enhanced aircraft, the ZC and PCs are replaced by the Air Conditioning System Controllers (ACSC). All of the functions of the ZC and PCs are incorporated in the ACSC.

* To control the pack outlet temperature, the PC modulates the BYPASS VALVE and the RAM-AIR INLET doors.

* The FCV (Flow Control Valve) is pneumatically controlled to “closed” if:

1) The pneumatic pressure is < 10 psi (spring-loaded closed)

2) The compressor discharge temperature is > 230 – 260°C

• The MIXER UNIT mixes hot air coming from packs with the warmer air recirculating from the cabin.

• OUTFLOW VALVE has 3 electrical motors:

- one controlled by CPC 1

- one controlled by CPC 2

- one controlled by MANUAL PRESS CONTROL

• CPC 1 and CPC 2 swap at each flight.

• COCKPIT RAM AIR P/B: If both packs are off, and APU bleed-air pressure is not available, it will open RAM AIR DUCT that will bring ram air directly to the mixing unit.

• TRIM AIR PRESSURE REGULATING VALVE regulates air 4 PSI above requested to improve OUTFLOW VALVE performance.

• Each pack controller (PC) consists of one primary (normal mode) and one secondary computer (back up). When primary and secondary computer fail, the solenoid of the pack anti-ice valve is de-energized and the pack outlet temperature is pneumatically

controlled by the anti-ice valve to 15°C.

• The Anti-Ice Valve is pneumatically operated and electrically controlled by a solenoid (S).

• If the pack controller (PC) primary computer fails, the secondary computer controls the bypass valve with the ram air flaps signaled to full open position.

• If both pack computers of the Pack Controller (PC) fail, the corresponding pack outlet temperature is fixed by the pack anti-ice valve (15°C).

• ACSC 1 (AIR CONDITIONING SYSTEM CONTROLLER) only is responsible for the flow calculation and sends flow demand signals for ASCS 2.

• The main function of the A.ICE valve is to remove ice build-up at the condenser from components downstream of the turbine outlet (condenser tubing, temperature sensors, check valves, mixing unit).

• Both packs outlet temperatures are normally controlled to the coldest temperature demand of the three zones.

• Normally the mixing unit allows the cockpit to be supplied from pack 1 and fwd and aft cabins from pack 2.

• The trim air Pressure Regulating Valve regulates the pressure of the air supplied to the trim air valves, 4 psi above the cabin pressure.

• When the zone controller primary computer or the trim air system fails, the secondary computer operates as backup. Pack 1 controls the cockpit temperature and pack 2 controls the cabin temperature to a fixed value (24°C fix value).

• When both computers of the zone controller fall, each pack is controlled to deliver a fixed pack outlet temperature.(20°C for pack 1,10°C for pack 2).

• The Cabin Intercommunication Data System (CIDS) Director 1 sends a data signal for ACSC 1, and the CIDS Director 2 sends a signal for ACSC 2 for temperature regulation (+ or - 2.5 C) from the Flight Attendant Panel (FAP).

• Any zone duct temperature higher than 88°C causes the hot air Pressure Regulating Valve (PRV) and trim air valves to close electrically.

• The operation of the inlet and the outlet isolation valves and the extract fan is controlled by the cargo ventilation controller.

• When the duct temperature goes above 88°C, the FAULT light on the HOT AIR switch 16HC on the overhead panel comes on and the pressure regulating-valve 11HC closes. This overheat condition is latched by the heating controller. When the duct temperature decreases to 70°C the system can be reset.

• The system is automatically controlled by the Avionics Equipment Ventilation Computer and no crew action is required.

• In OPEN CIRCUIT CONFIGURATION, ambient air, drawn through the SKIN AIR INLET valve by the BLOWER FAN, is blown into the system. The air, after cooling avionics equipment, is drawn by the EXTRACT FAN directly overboard. (skin temp over 5°C)

• In CLOSED CIRCUIT CONFIGURATION, the extracted avionics equipment air goes, through the SKIN EXCHANGER ISOLATION valve, into the SKIN HEAT EXCHANGER to be cooled.

• The avionics equipment is cooled with air in a partially open circuit when the skin temperature is above + 35°C.

• On ground, the ADIRU & AVNCS VENT light illuminates amber on the external power panel 108VU, accompanied by the horn activation.

• In case of failure of both packs, an emergency ram air inlet flap can be opened for A/C ventilation or smoke removal.

• In normal operation, pressurization control is fully automatic: 1 outflow valve including 3 motors, 2 for automatic and 1 for manual ctrl..2 safety valves located on the aft pressure bulkhead.

• One controller operates the system at a time according to flight profile data and A/C configurations. The second controller is in active stand-by with automatic changeover after each flight or in case of failure of the active one.

• When manual mode is used, the manual part of controller 1 operates only as a back- up indication circuit processing outputs for indicating and monitoring.