(c)  
The torque motor of the flow-control-and-shutoff valve

 (d)  
The low-limit-control valve, when the system is not in the STBY-N mode.

 M.
Standby-Pack-Temperature Controller (Fig. 10A)

___________________________________
 (1)  The standby-pack-temperature-controller is a box which has two microprocessors. Each microprocessor controls the left or the right air cooling pack. They only operate when the applicable cooling pack system is in the STBY-N mode. The microprocessors also monitor parts of the cooling pack system for failures. The front panel of the standby pack temperature controller has lights that come on when a failure occurs. It also has switches and instructions to do BITE.
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757
MAINTENANCE MANUAL

Pack Temperature Controllers
Figure 10A (Sheet 1)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757
MAINTENANCE MANUAL

Pack Temperature Controllers
Figure 10A (Sheet 2)

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MAINTENANCE MANUAL

 (2)  
In the STBY-N mode, the standby-pack-temperature controller controls the low-limit-control valve. The position of the low-limit-control valve controls how fast the air cycle machine turns. The speed of the air cycle machine controls the compressor outlet temperature and the air-cooling-pack-outlet temperature.

 (3)  
The BITE function of the standby-pack-temperature controller monitors parts of the cooling pack system for failures. It does not store the failures. It only does a go/no-go test of the controller circuit functions and the applicable sensors.

 N.
Pack Temperature Sensor (Fig. 11)

_______________________
 (1)  
For each air cooling pack, two pack temperature sensors supply a resistive signal of the temperature at their positions. One pack temperature sensor sends a signal to the standby-pack-temperature controller. The other pack temperature sensor sends a signal to the applicable (left or right) automatic-pack-temperature controller. The pack temperature sensors are installed on the outlet of the water extractor.

 (2)  
Each pack temperature sensor has two series-connected glass-sealed thermisters in a stainless steel probe. The electrical resistance of the thermister changes as an inverse, non-linear function of the temperature.

 (3)  
The automatic-pack-temperature controller compares the the pack demand signal (from the zone temperature controller) with the pack temperature sensor signal. The difference between the signals is the pack error. Then it uses the pack error to control the positions of the ram air door actuators and the temperature control valve. The standby-pack-temperature controller compares the pack temperature sensor signal to a value of 40°F (4°C) to get the pack error. Then it uses the pack error to control the position of the low-limit-control valve.

 O.
Altitude Switches (Fig. 11)

_________________
 (1)  Each altitude switch sends a signal to the applicable (left or right) automatic pack temperature controllers. The controllers change the minimum temperature limits of the air cooling packs to make allowance for the altitude. The switches are installed in the forward end of the left ECS bay, to the left of the cabin air supply check valve.
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