30-41-00
 ALL  ú ú 01 Page 10 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 CONTROL CABIN WINDOW ANTI-ICING SYSTEM - TROUBLE SHOOTING
_________________________________________________________
 1.  General
_______
 A.  AIRPLANES WITHOUT BITE IN THE WINDOW HEAT CONTROL UNIT;
 Refer to the data that follows:

 (1)  
This procedure contains the trouble-shooting for the control cabin window anti-icing system. It has figures that contain trouble-shooting procedures for specified failures.

 (2)  
If you can identify the failure, follow the instructions in the appropriate figure.

 (3)  
If you can not identify the failure, do a test of the system (AMM 30-41-00/501) to find the failure.

 B.  AIRPLANES WITH BITE IN THE WINDOW HEAT CONTROL UNIT; This procedure contains the trouble-shooting for the control cabin window anti-icing system with a window heat control unit that has built in test functions.
 2.  Fault Isolation Tips
____________________
 A.  Make sure the connections to the sensor, the window and the window heat control units are tight and free from corrosion.
 NOTE: Loose or dirty connections can make the overheat light come
____ on intermittently or in-flight only. Loose or dirty connections can also cause the window anti-ice system to not operate.
 B.  If ice or fog forms on the window, it is possible that the wires which supply power to the window are not connected to the correct tap at the window heat control unit. Do a check of the electrical resistance of the windows (AMM 30-41-21/501).
 C.  Pressurization of the airplane can make the OVERHEAT light come on intermittently. Pressurization makes the window bend. This can make the sensor in the window pull apart and become an open circuit. Then, the window heat control unit turns on the OVERHEAT light. When the airplane is not pressurized, the window does not bend. The sensor is satisfactory and the OVERHEAT light goes off. If you think this occurs do these steps:
 (1)  
Pressurize the airplane.

 (2)  
Make sure the resistance of the window sensor is less than approximately 358 ohms.

 (3)  
If the resistance is more than 358 ohms do this check of the spare sensor.

 (a)  
Measure the resistance of the spare sensor.

 (b)  
Make sure the resistance of the spare sensor is less than approximately 358 ohms.

 (c)  
Replace the window if the resistance of the two sensors is not satisfactory.

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 30-41-00
 ALL  ú ú 02 Page 101 ú Nov 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (4)  Do the trouble-shooting in Fig. 101 if the trouble stays.
 3.  Fault Isolation Procedures
__________________________
 Fig. 101 The OVHT light comes ON Fig. 102 Power ON light does not come ON Fig. 103 Window Anti-ice lights do not operate correctly
 when the light test switch is in the TEST position Fig. 104 When you release the light test switch, the Window Anti-ice lights stay ON
 Fig. 105  The Master Caution and the OVHT lights do not operate correctly when you put the test switch in the OVHT position
 Fig. 106 During a system test, the voltage at the No. 1 and No. 2 windows is not correct Fig. 107 Window No. 4 or No. 5 Anti-ice does not operate correctly
 4.  AIRPLANES WITH BITE IN THE WINDOW HEAT CONTROL UNIT; Fault Isolation
 A.  Initial Evaluation
 (1)  
Set the window anti-ice switch to ON.

 (2)  
Press the "FAULT HISTORY" switch on the WHCU.

 (3)  
If any of the red LEDs come on, then do these steps:

 (a)  
Press the "BIT VERIFY" switch on the WHCU.

 (b)  
If any of the red LEDs come ON, then do the Procedure below.

 (c)  
If only the green "BIT TEST OK" LED comes ON, then there was an intermittent fault. 1) Press the "BIT LAMP RESET" and the "LAMP TEST" switches on
　
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