30-41-00
 ALL  ú ú 01 Page 6 ú Jan 28/02

A

757
MAINTENANCE MANUAL

 B. Ground Test (Fig. 2, 3, and 4)
 (1)  
The ground test of the window heat system requires the four WINDOW HEAT switches to be ON (latched-in). The system is tested by the WING ANTI-ICE WINDOW/PROBE HEAT switch on the miscellaneous test panel. The switch is a momentary action, center off type. The test is done by holding the switch in the WINDOW/PROBE HEAT position. Each window heat control unit (WHCU) performs a continuity check of its window heaters, a resistance check (open/short test) of its temperature sensors, and a check of its own functions. The overheat circuits are checked last. Successful completion of this test causes the amber INOP lights on the window heat control panel to illuminate. When all four INOP lights are illuminated the system is OK. Both WHCUs (all six window channels) are reset to normal flight condition by releasing the WING ANTI-ICE WINDOW/PROBE HEAT switch. (The switch returns to the center position.) The test takes 3 seconds.

 (2)  
Window Heat Control Unit Testing

 (a)  
Failure of an INOP light to illuminate during the ground test indicates a system failure. The failed channels are then associated with the switch containing the off light. The WHCU controlling the failed channel is then tested to find the defective channel components.

 (b)  
Built in test equipment of the WHCU is started by pressing the BIT/VERIFY pushbutton on the front of the unit. If no fault is found, only the TEST COMPLETE light on the WHCU will be illuminated. The unit returns automatically to normal flight condition within three minutes of test initiation. If a fault is found, the defective component is indicated by the appropriate light on the unit.

 (c)  
The lights on the WHCU are checked by pressing the PRESS/TEST pushbutton. All lights should be illuminated.

 C. Control
 (1)  
To place system in operation, apply electrical power to main ac buses (Ref 24-22-00).

 (2)  
Make sure these circuit breakers are closed on the miscellaneous relay panel P70:

 (a)  
WINDOW HTR 1L

 (b)  
WINDOW HTR 2R

 (c)  
WINDOW HTR 3R

 (3)  
Make sure these circuit breakers are closed on the right
 miscellaneous electrical equipment panel P37:

 (a)  
WINDOW HTR 1R

 (b)  
WINDOW HTR 2L

 (c)  
WINDOW HTR 3L

 (4)  
Make sure these circuit breakers are closed on the overhead circuit breaker panel P11:

 (a)  WINDOW HEAT TEST
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