S 864-017

 (4)
Remove the DO-NOT-CLOSE tags and close these circuit breakers:

 (a)  6F28, ZONE TEMP CONT AC
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747-400 MAINTENANCE MANUAL
 (b) 6F29, ZONE TMEP CONT DC
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747-400 MAINTENANCE MANUAL
 AIR CONDITIONING PACK TEMPERATURE CONTROL SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________________________
 1.  General (Fig. 1 and Fig. 2)_______
 A.  The air conditioning pack temperature control system controls the output temperature of the air conditioning packs to meet cabin temperature requirements. A pack temperature controller positions the turbine bypass valve and ram air doors for each pack to drive the pack discharge temperature to the demand temperature required by the zone temperature controller.
 B.  The packs are controlled to a common discharge temperature. This temperature is determined by the zone demanding the lowest supply temperature. Air conditioning pack output temperature is controlled within the limits of 35 to 135°F (2 to 57°C).
 C.  The air conditioning pack temperature control system consists of two pack temperature controllers which command the temperature regulating components of each air conditioning pack. For each pack there is a turbine bypass valve, a ram air inlet door and actuator, a ram air exit door and actuator, and a pack discharge temperature sensor.
 2.  Pack Temperature Controller (Fig. 2)___________________________
 A.  Two identical automatic pack temperature controllers control and perform fault detection of pack temperature regulating components for all phases of flight. The controllers are located on the E2-3 electronics shelf in the main equipment center.
 B.  Each pack temperature controller receives input from the following sources:
 (1)
Zone Temperature Controller

 (2)
ECS Miscellaneous Card

 (3)
Pack 1, 2, and 3 Discharge Temperature Sensors

 (4)
Pack 1, 2, and 3 Ram Air Inlet Actuators

 (5)
Pack 1, 2, and 3 Ram Air Exit Actuators

 (6)
Pack 1, 2, and 3 Turbine Bypass Valves

 (7)
Air/Ground Relay System

 (8)
Central Maintenance Computer System

 C.  Both controllers continuously receive input data, but one waits on standby while the other acts as the primary controller to command the ram air inlet and exit actuators and turbine bypass valves for all packs. Normally, primary control is alternately assigned to controller A and controller B on alternate flights. If the primary controller fails, the system will switch controllers automatically.
 D.  The controller has a continuous self-test feature which isolates faults in the pack temperature control system and transmits them to the EIU's for annunciation on EICAS and for fault isolation by the central maintenance computer system. A ground test of the system may be performed with the central maintenance computer system.
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A 747-400 MAINTENANCE MANUAL
RAM AIR IN

NOTE: DIAGRAM SHOWN FOR ONE AIR CONDITIONING PACK, OVERBOARD

OTHER PACKS SIMILAR.
DISCHARGE
Air Conditioning Pack Temperature Control Block Diagram
Figure 1

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