C. The overheat indicating light is controlled by its respective window heat control switch and the auxiliary contacts of the overheat relay in the window heat control unit. When 28 volt dc power is available the light is illuminated whenever the overheat relay does not agree with the control switch 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 completes a circuit to ground through these switches for the master caution indicating lights.
7. Test Switch
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 overhead panel (Figs. 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.
8. Window No. 5 Thermal Switch
A. The window No. 5 thermal switch is a temperature sensitive, bimetallic, single pole, snap action switch with normally closed contact points which open at 110° (+ 10°)F and close at 90° (+ 10°)
F. The switches are spring mounted near the lower edge of each of the No. 5 windows and regulates the application of power to the No. 4 and 5 windows of its respective side (Figs. 1 and 2).
9. Control Module P5-9
A. The P5-9 module in the pilots' P 5 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, see paragraphs 4 (control switch), 6 (indicator lights), and 7 (test switch). See Section 30-09-111 for removal, installation, and adjustment/test instructions.
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May 15/68 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 30-41-0 Page 7
10. Operation
A. Each of the No. 1 and 2 window heat systems are operated by the actuation of the respective control switch to the ON position (Fig. 2). With either switch for either side in the ON position, 28 volt dc and 115 volt-ac control power will be directed from the load control center to the window heat control unit for its respective window, and 115-volt ac heating power will be directed to windows No. 4 and 5 by the side switch of the respective side. The No. 1 and 2 windows are maintained at 107 + 7/-7°F by the window heat control unit and the No. 4 and 5 windows are regulated between 80 to 120°F by the window thermal switch on the No. 5 window.
B. With control power supplied to the heat control unit in the absence of an overheat condition the control unit overheat circuit will direct 115-volt ac heating power from the load control center to the control unit temperature control circuit for modulation to the control unit heat transformer . If the window is below 100°F the window heat sensor will signal the temperature control circuit for heating power and the temperature control circuit will gradually increase power to the control unit transformer circuit. The transformer circuit in turn will apply the preselected voltage to the terminal strip on the E3-3 electrical shelf then directly to the window. The window heating power will continue to increase until the temperature control circuit output reaches full operating power within 3 minutes or until the window sensor detects the window temperature approaching operating temperature. As operating temperature is approached the temperature control circuit will begin to decrease power until power output and heat dissipation from the window are held in equilibrium at the required operating temperature. When the temperature control circuit supplies power to the control unit transformer it also supplies a ground for the power on lamp driver circuit, illuminating the ON light and providing visual indication that power is actually being supplied to the window. The light will remain illuminated as long as the control unit power output exceeds approximately 5 watts. The window heat control unit may be confidence tested for power output through the use of the system test switch. Placing the switch in the POWER position completes a circuit to ground from the temperature control circuit which forces the temperature control circuit to full power output, regardless of window temperature.
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