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757 MAINTENANCE MANUAL
FLIGHT COMPARTMENT WINDOW ANTI-ICING - DESCRIPTION AND OPERATION
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General
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A. The captain's and first officer's No. 1, No. 2 and No. 3 windows are heated. The main components are the windows, window heat control units, the window heat control panel, and the miscellaneous test panel. System power comes from the main left 28-volt dc bus, and the main left and right 115-volt ac buses.
Component Details (Fig. 1)
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A. Windows
(1) A conductive film or wire net between the outer pane and the core provides electrical heating of the window.
B. Window Heat Control Unit (WHCU)
(1)
Two window heat control units (WHCUs), each with built-in-test equipment (BITE), regulate heating and isolate system failures. The left WHCU is on shelf 2 of left forward equipment center rack E1. The right WHCU is on shelf 1 of E1. BITE pushbuttons, fault indicating lights, and BITE instructions are on the unit face.
(2)
The WHCU uses 200 volts (No. 1 window) and 115 volts (No. 2 and 3 windows) ac power for heating. Twenty-eight volt dc power is used by the WHCUs for system testing.
C. Window Heat Control Panel
(1) Window heat control panel M10395 is located on pilots' overhead panel P5. The panel contains four WINDOW HEAT switches to control window heating.
D. Miscellaneous Test Panel
(1) Miscellaneous test panel M10398 provides for testing of the window
heat system. The test panel is on right side panel P61.Operation
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A. Functional Description (Fig. 2, 3, and 4)
(1)
Each window has its own control channel, temperature sensor, and heater. The control channel regulates power to the window heater in response to demands from the sensor. The sensor keeps window temperature at a preset value.
(2)
Each window heat control unit (WHCU) contains one front (No. 1) window channel and the opposite two side (No. 2 and No. 3) window channels.
(3)
Pressing the WINDOW HEAT switches on window heat control panel M10395 to ON turns on window heating. These are push on/push off switches which latch in when ON. Each switch contains a white ON light and an amber INOP light.
(4)
The L and R FWD switches control heat to the respective No. 1 windows. The L and R SIDE switches control heat to the respective No. 2 and 3 windows.
(5)
The amber INOP switchlight illuminates to indicate a failure in the heating channels controlled by that switch. A window heat failure also causes a message to appear on the EICAS display (Ref 31-41-00).
NOTE: INOP light may illuminate with outside ambient
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