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BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details.

AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FAN INLET DIFFUSER HOUSING AND CK VLV

Purpose
The fan inlet diffuser housing connects the dual heat exchanger to the ACM fan and ram air exhaust duct.
The fan bypass check valve permits air to go around the ACM fan at higher ram air flow.
Physical Description
The fan inlet diffuser housing is a metal container with flexible connections at the ram air inlet and fan bypass. An inner assembly separates the air flow that goes to and from the ACM fan.
The fan bypass check valve is a flapper-type valve.
Training Information Point
The fan inlet diffuser housing has a strap that attaches to the upper support fitting and to airplane structure (not shown). The strap supports the housing when the ACM or dual heat exchanger is removed. Make sure you install this strap when you install the fan inlet diffuser housing.
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FAN INLET DIFFUSER HOUSING AND CK VLV

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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -CONTROL

General
The CTCs control the related air conditioning pack. The CTCs usually set the packs to keep the temperature in the mix manifold to a calculated value and to keep pack outlet temperatures within 10F (5.5C) of each other.
The calculated temperature value for the mix manifold is called integrated mix manifold temperature error (IMMTE) reference. The IMMTE reference is based on cooling and heating requirements of the zones that usually get conditioned air from the mix manifold. The right CTC usually calculates this reference. The left CTC follows the right CTC. The left can make the calculation if the right CTC fails. See the zone temperature control and indication section for more information about the calculation of the IMMTE reference (SECTION 21-61).
The left and right CTCs can control the related pack outlet temperature to different values. This occurs when the flight deck needs more cooling than the request by the IMMTE reference. If the flight deck needs more cooling, the left CTC controls the left pack outlet temperature to satisfy the flight deck requirements. The right CTC controls the right pack outlet to satisfy the IMMTE reference.
The left and right CTCs control the temperature of air from the related pack by direct adjustment of these components:
*
Second stage turbine bypass valves (TBV)

*
Low limit valves (LLV)

* Ram air door actuators.
The CTCs use the economy cooling valve (ECV) to bypass the water removal part of the pack. The CTC opens the ECV when water removal is not necessary or when the CTC must increase airflow into the airplane. The CTC controls the economy cooling valve through the ELMS electronics (ELEX) unit.
For usual control, the CTCs set the speed and direction of valve/ actuator movement based on the difference between actual (RVDT) and desired position. Desired position is a CTC calculated position for valve/actuator based on these conditions:
*
Pack on or off, pre-positioning for off

*
Pack control, usual or backup.

When a pack is on, the desired position for a valve or an actuator is usually set to a preset schedule for each valve/ actuator. The schedules for the ram air door actuators, TBV, and LLV do these functions:
*
Keeps the use of ram air to a minimum

*
Adjust ram air flow to keep ACM fan surge margins

*
Keeps the compressor outlet temperatures within limits.

The position schedules for the ram air door actuators and the TBV and LLV automatically adjusts for low (less than.5 MACH) and high (more than or equal to.5 MACH) airspeeds. The schedule for the ram air door actuators also adjusts for the economy cooling mode.
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -CONTROL

Ram Air Door Actuator
CTC control of the ram air inlet actuator has these functions:
*
Limit closed position if the LLV or the TBV fails (ACM surge protection)

*
Limit compressor outlet temperature (prevents compressor overheat)

*
Keep the mix manifold temperature equal to or more than 35F (2C) if the TBV is full open (prevents water freezing in mix manifold)

*
Control pack outlet temperature to satisfy the IMMTE reference (valve/actuator preset schedules).
　
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