*
EEC -gives pressure information about the HP source to the primary mode only.
Training Information Point
When a latched condition occurs, do not put the applicable engine bleed switch to out and then back to in. This will reset the latched condition and any active fault will disappear. Use the Fault Isolation Manual to troubleshoot a latched condition.
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General
The ASCPC changes the position of the FAMV and the PRSOV for temperature control. The primary and backup modes use torque motors in the HPFAC and the PRSOVC to change the amount of control air to the valves.
The primary mode can change the position of the fan air modulating valve (FAMV) to give the usual temperature regulation function. The primary and backup modes can change the position of the pressure regulating and shutoff valve (PRSOV) to give these functions:
*
Temperature limiting -primary and backup modes
*
Overtemperature protection -primary and backup modes
*
Flow limiting -primary mode.
The pneumatic mode gives no temperature control of any type and does not give flow limiting. When the backup mode or the pneumatic mode gives control, the FAMV goes to the default position of fully open.
Temperature Regulation
The primary mode usually controls the precooler outlet temperature to one of these fixed values:
*
250F (121C): if the CTC requests lower temperature and wing anti-ice off
*
320F (160C): during cruise when both engines are operating and 250F (121C) is not being commanded
* 380F (193C): usual value.
Element 2 in the manifold temperature sensor (TM2) gives the temperature information to the primary mode. If element 2 fails, the primary mode gets temperature information from element 1 (TM1) through the backup mode.
The primary mode usually uses the FAMV to control the precooler out temperature. The position of the FAMV is set to control the amount of fan air allowed through the precooler. The fan air cools the engine bleed air as it goes through the precooler.
The primary mode sets the usual temperature of 380F (193C) to make sure sufficient heat is in the air for the wing anti-ice system.
If the wing anti-ice system is off, the primary mode can set the temperature to 250F (121C) if the related cabin temperature controller (CTC) tells the ASCPC that a lower temperature is necessary.
Primary mode of the ASCPC sets the precooler out temperature to 320F (160C) if all of the following are true:
*
250F (121C) precooler out temperature is not set
*
The FMC is in cruise phase of flight
*
Both engines are operating.
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See the functional description part of the air conditioning pack cooling and mix manifold temperature control section for more information about CTC request for lower precooler out temperature (SECTION 21-52).
Temperature Limiting
The primary and backup modes give the same temperature limiting function. When the precooler out temperature is 450F (232C) or more, the applicable mode sets the position of the PRSOV to limit the amount of bleed air allowed through the precooler.
Temperature information comes from TM2 for the primary mode or TM1 for the backup mode.
When the precooler out temperature is equal to or more than 450F (232C), the primary and backup modes command the PRSOV towards closed to limit bleed air flow. When bleed air flow is limited, the bleed air temperature usually goes down.
Overtemperature Protection
The engine bleed air overtemperature protection function is enabled at the same time by the primary and backup modes. Temperature information comes from TM2 for the primary mode or TM1 for the backup mode.
If the precooler out temperature is more than 490F (254C), the primary and backup modes command the PRSOV to the fully closed position.
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