F88259
515  Window Heat Indicating Circuit 
Aug 01/74  Figure 3  30-41-0 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

C.  If the window heat sensor detects a window temperature above 145°F while power is being applied to the window, the temperature control circuit will de-energize the control unit overheat circuit. Having the overheat detection section of the temperature control circuit operate only while power is actually being applied to the window allows a lower overheat trip setting, without nuisance system trips and lockouts under hot summer day conditions. With the control unit overheat circuit de-energized the 115-volt ac heating power will be cut off from the temperature control circuit, removing window heat and turning off the power ON indicating light. Also, whenever the control unit overheat circuit is de-energized with the control switch in the ON position or energized with the control switch in the OFF position, the overheat indication circuit through the control switch will be completed to ground through the control unit overheat circuit. This will illuminate the overheat indication light and after a 1-second delay, activate the master caution indicating circuit, illuminating the master caution and anti-ice indicating lights. The master caution and anti-ice lights will remain illuminated until the master caution indicating circuit is reset by pressing the master caution light cover. The overheat indication light will remain illuminated until the system is reset by momentarily turning the control switch to the OFF position. While the system is in operation the control unit overheat detection system may be confidence tested through the use of the system test switch. Placing the switch in the OVERHEAT position completes a circuit to ground from the temperature control circuit which forces the temperature control circuit to apply power to the window and then simulates the overheat condition, de-energizing the control unit overheat circuit and illuminating the master caution, anti-ice and system overheat indicating lights.
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30-41-0 Page 10  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 15/73 

CONTROL CABIN WINDOW ANTI-ICING SYSTEM - TROUBLE SHOOTING
1.  General
A.  The most practical method for isolating any trouble in the control cabin window anti-icing system is to utilize the control cabin window anti-icing - adjustment/test procedure.
B.  Before using the following trouble shooting chart, prepare to test the window anti-icing system in accordance with adjustment/test procedure. Proceed with test to extent practical to determine extend of trouble. The following trouble symptoms are presented in the order in which they would occur during system test.
2.  Trouble Shooting Chart
NOTE:  In this trouble shooting chart, the abbreviation "WHCU" is used for the window heat control unit.
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Feb 20/93  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  30-41-0 Page 101 

TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Circuit breaker continues to trip (power on condition)  Defective airplane wiring, P5-9 module, heat sensor, or control unit  Remove the applicable WHCU. Look at WDM 30-41-11 or 30-41-12. Check for a direct short between the pins of the plug on the WHCU (except there should be a short between pins 6 and 10 on the plug for the “A” connector and between pins 5 and 7 on the the plug for the “B” connector). IF -Short exists -Remove the applicable connector D638 or D644 from the P5-9 window and pitot heat module. Check for a direct short between the pins of the WHCU connectors on the E3-3 rack. Also check for a short to ground from any of the pins (except pins 6 and 10 of the “A” connector and pins 5 and 7 of the “B” connector should all be  grounded). IF -Short exists -No short exists - Check window heat sensor for short, faulty window lead-in wire, and faulty window conductor bus. IF -Condition exists - Replace control unit Repair wiring between control unit plug and P5-9 module plug Replace or repair defective part Replace faulty part 

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B48330 B51139 B51154 B51206 B51218 B51250 B51265 B51319 B51376 B51391 B51408
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Feb 20/93  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  30-41-0 Page 103 

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