30-41-00
ALL ú ú 01 Page 7 ú Mar 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
B. The power indicating light is controlled by the power on lamp driver short circuit protector circuit in the respective window heat control unit. When 28-volt dc power is available, the light is on whenever the power-on lamp driver circuit in the control unit exceeds approximately 5 watts of power.
C. The overheat indicating light is controlled by the respective window heat control switch and the auxiliary contacts of the overheat light relay in the window heat control unit. When 28-volt dc power is available, the light comes on if the overheat light relay is de-energized while the control switch is in the ON position (switch on - relay energized, switch off - relay de-energized.)
D. The master caution warning system consists of four time delay circuits, one for each of the overheat indication circuits, and a warning latch circuit. The reaction time of the overheat relay may cause a momentary overheat signal when the control switch is turned on. To avoid nuisance trips of the master caution system, the signal is directed first to the delay circuit. If the signal persists for approximately one second, the delay circuit provides an impulse to the latch circuit which then provides a ground for the master caution lights through the overheat relay. The latch circuit will remain conductive until the power is interrupted either through the use of the master caution light reset or by resetting the window heat control system. The warning latch circuit may also be tripped by the master caution light recall switch or master light test switch and complete a circuit to ground through these switches for the master caution indicating lights.
Test Switch
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A. The window heat test switch is an eight pole, double-throw, with center OFF position and momentarily on at both extremes, toggle actuated switch. The switch has momentary POWER and OVERHEAT positions and is located between the window heat control switches on the overheat panel (Fig. 1 and 2). The switch provides a ground for the power test input on each of the four window heat control units (pin 19) when placed in a POWER position, and similarly provides a ground for each of the overheat test inputs (pin 12) when placed in the OVERHEAT position.
Window No. 5 Thermal Switch
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A. The window No. 5 thermal switch is a temperature sensitive, bimetallic, single pole, snap action switch with normally closed contract points which opens at 110° |10°F and closes at 90° |10°F. The switches are spring mounted near the lower edge of each of the No. 5 windows and regulate the application of power to the No. 4 and 5 windows of the respective side (Fig. 1 and 2).
Control Module P5-9
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A. The P5-9 module in the pilots' P5 overhead panel contains all the switches and indicating lights for the control cabin window anti-icing system. The P5-9 module also contains the switches and indicating lights for the pitot-static and temperature probe anti-icing system. For description and operation of module switches and indicating lights, refer to par. 4 (control switch), 6 (indicator lights), and 7 (test switch). Refer to AMM 30-09-11 for removal, installation, and adjustment/test instructions.
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