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747-400
MAINTENANCE MANUAL

 S 034-025
 (4)
Disconnect the electrical connector from the thermostat.

 S 024-027

 (5)
Remove the thermostat from the tank.

 S 034-026

 (6)
Remove the O-ring from the thermostat for re-use.

 TASK 30-71-08-404-029
 5. Potable Water Tank Thermostat Installation (Fig. 401)
__________________________________________
 A. References
 (1)
AMM 12-14-01/301, Water System Servicing

 (2)
AMM 24-22-00/201, Manual Control

 (3)  
AMM 25-52-01/401, Containerized Cargo Compartment Ceiling and Sidewall Lining

 (4)
AMM 30-71-00/501, Waterline and Waste Drain Heaters

 (5)
AMM 38-10-00/201, Potable Water System

 (6)
AMM 38-15-00/201, Water System Pressurization

 (7)
AIPC 30-71-07

 (8)
SSM 30-71-01, SSM 30-71-02, SSM 30-71-03

 (9)
WDM 30-71-11, WDM 30-71-12, WDM 30-71-13, WDM 30-71-14, WDM 30-71-15

 B. Access
 (1)  Location Zone 125 thru 152 Lower Lobe (Refer to WDM for heater locations)
 C. Procedure
 S 434-030
 (1)
Put the O-ring on the thermostat

 S 424-031

 (2)
Put the thermostat into the tank, and tighten.

 S 434-032

 (3)
Install the electrical connector.

 (4)
Do this task: "Water Servicing (Fill)" (AMM 12-14-01/301).

 (5)
Supply electrical power (AMM 24-22-00/201).

 (6)
Do this task: "Pressurize Water System" (AMM 38-15-00/201).

 S 614-034
 S 864-033
 S 864-035
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747-400 MAINTENANCE MANUAL
 (7)  S 214-036Make sure that there are no leaks at the tank thermostat.
 (8)  S 864-037Remove the DO-NOT-CLOSE tags and close these circuit breakers: (a) P414, Left Power Distribution Center 1) 414A23, WATER LINE HTR B 2) 414D4, WATER LINE HTR A
 (9)  S 714-038Do a test of the tank heater (AMM 30-71-00/501).
 S 414-039

 (10)
 Install the cargo liners or floor panels which were removed (AMM 25-52-01/401).

 S 114-040

 (11)
 Do this task:  "Potable Water System Cleaning (with Disinfectant)" (AMM 38-10-00/201).

 S 864-021

 (12)
 Remove the electrical power (AMM 24-22-00/201).

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747-400 MAINTENANCE MANUAL
 ICE DETECTION SYSTEM - DESCRIPTION AND OPERATION
________________________________________________
 1.  General (Fig. 1)_______
 A.  Two independent ice detection systems provide flight deck indication of icing conditions and automatic activation of wing and engine inlet thermal anti-ice systems. Components used by the ice detection systems are the two ice detector probes, the wing and nacelle anti-ice control switches on the anti-ice/rain removal module, and the EIU's and EICAS display. The left ice detection system is powered by 115 volts ac from the 115 vac bus 1 and the right system from the 115 vac bus 3.
 2.  Ice Detector Probe__________________
 A.  The ice detector probes are located on the lower front part of the fuselage just aft and below the pitot static probes.
 B.  The ice detector probe contains a magnetostrictive sensing element, a heater, and control cards. The sensing element is part of an electromechanical resonant circuit which oscillates at approximately 40 kHz. Ice buildup on the outer end of the sensing element lowers the resonant frequency by increasing the effective weight of the element. After a specific amount of ice has accumulated, the heater is activated to melt the ice and return the resonant frequency to its initial value.
　
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