A rotary variable differential transformer (RVDT) in the actuator sends the door position to the CTC.
Second Stage Turbine Bypass Valve
CTC control of the second stage turbine bypass valve has these functions:
*
Limit open position if ram air door actuator fails (ACM surge protection)

*
TBV full open if ACM fails (standby cooling, lets the pack continue to operate)

*
Change position to control pack flow if flow control valve is full open and pack in economy cooling mode (lets pack satisfy pack flow schedule)

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

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

EFFECTIVITY
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An RVDT in the valve sends the valve position to the related CTC.
Low Limit Valve
CTC control of the low limit valve has these functions:
*
Keep condenser inlet temperature more than or equal to 34F (1C) (prevents water freezing in the hot side of the condenser)

*
Control pack outlet temperature if TBV is full open and the mix manifold temperature less than the IMMTE reference or less than 35F (2C).

Economy Cooling Valve
The CTC tells the electrical load management system (ELMS) electronics unit to open or close the economy cooling valve (ECV). The ELMS electronics unit uses the economy cooling valve relay to set the position of the ECV. To open the valve, ELMS removes electrical power from the relay. This causes air pressure in the pack to open the valve. To close the valve, ELMS energizes the relay which gives 28v dc to a solenoid in the ECV. This causes air pressure in the pack to close the valve.
Sensors -Temperature and RVDT
The CTCs monitor pack temperature sensors and valve/ actuator RVDTs. The CTCs use this information for control, BIT and indications for the related air conditioning pack.
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -CONTROL

See the zone temperature control and indication section for more information about the pack temperature sensors (SECTION 21-61).
Indication -Standby Cooling
When the related CTC sets the related pack to operate in the standby cooling mode, the AIMS shows these two indications:
*
EICAS advisory message PACK MODE L (R)

*
STBY COOLING message on the air synoptic display.

The STBY COOLING message shows next to the related pack symbol.
See the cooling section for more information about the pack indications (SECTION 21-50).
Pack Off Positioning
The CTC sets the positions of the ram air door actuators, LLV, TBV and ECV when a pack is off. These are the related positions for a pack when the airplane is in the air:
*
Ram air inlet is at 0.98 percent of heating (98 percent closed)

*
LLV is at 0.00 percent of heating (full closed)

*
TBV is at 0.15 percent of heating (part open)

*
ECV is closed.

These are the related positions for a pack when the airplane is on the ground:
*
Ram air inlet is at 0.00 percent of heating (full open)

*
LLV is at 0.00 percent of heating (full closed)

*
TBV is at 0.00 percent of heating (full closed)

*
ECV is closed.

ASCPC Interface
The ASCPCs monitor the compressor and pack discharge temperatures. The ASCPCs have their own temperature sensors, they do not use the same sensors as the CTCs.
The related ASCPC uses the compressor and pack discharge temperature information to set the related pack to off if any of these conditions occur:
*
Compressor overheat more than 490F (254C) for 5 seconds

*
Pack overheat, 210F (99C) for 10 seconds and the related CTC has failed.

The related ASCPC also uses the temperature information to keep discharge temperatures in limits when it gives backup pack flow control.
See the pack flow control section for more information about backup pack flow control (SECTION 21-51).
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AIR CONDITIONING -PACK CLG AND MIX MANIFOLD TEMP CTRL -FUNCTIONAL DESCRIPTION -PACKS

General
The left CTC controls the left pack, and the right CTC controls the right pack.
In full air cycle machine (ACM) operation, the CTC controls the pack internal air temperatures and the pack output air temperature by adjustment of these components:
　
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