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Central Maintenance Computer System
C. The zone temperature controller compares the selected temperature for each zone with the actual temperature received from the zone temperture sensor. If the temperature values are not the same, the ZTC drives the corresponding trim air modulating valve more open or more closed to increase or decrease the zone temperature. The valve stops moving when zone duct temperature has been raised enough to make the required change in cabin temperature. Zone duct temperature information is supplied to the ZTC by the duct temperature sensor.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL
D. The controller has a continuous self-test feature which isolates faults in the zone 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.
5. Zone Temperature Sensor (Fig. 1)
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A. Each zone temperature sensor contains a motor-driven fan and 2 thermistor temperature sensors. One of the sensors provides compartment temperature information to the ZTC for temperature control and indication. The other sensor is referred to as the temperature bulb and provides the same information to the pack temperature controllers. The temperature bulb is only used when the zone temperature control system is in the backup mode.
B. The forward main deck and the aft main deck zones each have two temperature sensors, one in the forward end and one in the aft end of the zone. The average temperature of these two sensors is computed by the ZTC and is used to determine temperature demand for that zone.
6. Duct Temperature Sensor (Fig. 1)
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A. A duct temperature sensor is installed on each zone duct. The sensor supplies zone duct temperature information to the ZTC for temperature control and flight deck indication.
7. Duct Overtemperature Switch (Fig. 1)
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A. A duct overtemperature switch is installed in each zone duct. If air temperature in any zone duct exceeds 185° F (85° C), the overtemperature switch in that duct will close, causing the trim air shutoff valve to close and the SYS FAULT light on the master temperature selector panel to come on.
8. Master Trim Air Shutoff Valve (Fig. 1)
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A. The master trim air shutoff valve is a pressure regulating and shutoff valve which controls the supply of hot pneumatic bleed air to the trim air modulating valves. The master trim air shutoff valve consists of a 3.5-inch diameter butterfly valve, an upstream venturi, a shutoff solenoid, a downstream pressure sense input and a cabin pressure sense input. The valve is located at the aft center of the air conditioning bay.
B. The master trim air shutoff valve solenoid is energized in normal system operation, causing the valve to be open. The valve closes when the TRIM AIR switch on the cabin temperature control module is off or when a zone duct overheat occurs.
9. Lower Forward and Aft Cargo Trim Air Shutoff Valves (Fig. 1)
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A. The lower lobe forward and aft cargo trim air shutoff valves allow the trim air to the lower lobe cargo compartments to be turned off independently of other airplane zones.
10. Trim Air Modulating Valve (Fig. 1)
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A. There is a trim air modulating valve installed in the trim air duct for each zone. Each valve has a 115 vac motor, a butterfly valve, and a position potentiometer. The valve has a manual override and an external position indicator.
B. Each trim air modulating valve is commanded to drive more open when an increase in compartment temperature is required, or more closed when a decrease in temperature is required.
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