*
Low limit valve, set to full close
*
Second stage turbine bypass valve, modulating
*
Ram air doors, modulating.
Pack Sensor Failures
These sensors have an effect on pack operation if they fail:
*
Pack inlet differential pressure sensor, part of the pack flow sensor (not shown)
*
Compressor out temperature sensors 1 and 2
*
Condenser inlet temperature sensors 1 and 2.
The CTC has these two sources for pack inlet differential pressure: the pack flow sensor and the related ASCPC. If both sources fail, the pack stops.
See the pack flow control section for more information about the pack flow sensor (SECTION 21-51).
The CTC has three sources for compressor out temperature: compressor out temperature sensors 1 and 2 and the related ASCPC. If all sources fail, the pack stops.
The CTC has two sources for condenser inlet temperature, condenser inlet temperature sensors 1 and 2. If both fail, the pack operates in the standby cooling mode or stops.
See the zone temperature control and indication section for more information about the effects of other failed sensors on the air conditioning system (SECTION 21-61).
Ram Air Door Failure
If the temperature cannot stay within limits when there is a ram air door failure, the CTC decreases pack flow. The amount of decrease in flow has a relation to the temperature limits. The minimum flow is schedule 4. The serviceable pack increases flow to keep total fresh air ventilation constant.
If the ram air inlet door RVDT fails, the CTC moves the actuator to the full open position. The CTC sends a command to the actuator for the correct amount of time to set the door to full open. After this, the CTC identifies the condition as an actuator failure.
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -PACKS
Low Limit and Second Stage Turbine Bypass Valve Failures
If a low limit valve failure occurs, the CTC adjusts pack flow to keep condenser inlet temperature at or above 34F (1C). If a second stage turbine bypass valve failure occurs, the CTC sets the position of the ram air doors to control the pack outlet temperature. If the pack can not hold the necessary temperature, the CTC adjusts pack flow to control air temperature to the mix manifold.
If the low limit or second stage turbine bypass valve RVDT fails, the CTC moves the related valve to the 60 percent open position. The CTC times the movement of the valve to set it at 60 percent open. After this the CTC identifies the condition as a valve failure.
Single Pack Operation
In single pack operation, the CTC controls the TBV, LLV, ECV, and ram air doors actuators as usual to keep the necessary temperature in the mix manifold (IMMTE reference). The CTC also increases pack air flow to keep it close to the usual amount when two packs are on. The maximum flow has a limit so it is not more than the value set for flow schedule 2.
If the CTC can not keep pack flow or temperature (pack out temperature 5F (2.7C) more than IMMTE reference) at the necessary value, it can select one or all of these conditions to increase pack flow and to help control the pack out temperature:
EFFECTIVITY
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*
Operate the pack in the economy cooling mode if the conditions for this mode permit it
*
Tell the ASCPC to supply a lower precooler outlet temperature (250F, 121C) if the turbine bypass valve is not full open
*
Adjust the position of the second stage turbine bypass valve to control flow and temperature
*
If the second stage turbine bypass valve is fully open, or a lower precooler out temperature is not available (wing anti-ice if on) or does not let the pack operate to the necessary temperature, the CTC tells the ASCPC to supply a higher pneumatic pressure (6 psi bias for HPSOV control).
When the CTC must choose to control pack flow or pack out temperature, pack flow is usually first in the order of control. Pack overheat protection control, always overrides pack flow control.
See the pack flow control section for more information about the pack flow schedules (SECTION 21-51).
Single pack operation can cause the related lower recirculation fan (not shown) to stop if these conditions occur:
*
Airplane on the ground
*
Pack at maximum cooling
*
Mix manifold temperature 12F (6.7C) > IMMTE reference.
When a fan is set to off, this helps the related pack meet the necessary IMMTE reference by reducing the amount of cabin air put in to the mix manifold.
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -PACKS 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 空调 Air Conditioning(63)
