M18 LEFT WINDSHIELD WIPER MOTOR
NOTE: OFF - R1 & R2 DE-ENERGIZED LOW - R1 ENERGIZED R2 DE-ENERGIZED HIGH - R1 & R2 ENERGIZED
Windshield Wiper System Schematic
Figure 2

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747-400 MAINTENANCE MANUAL
 (c)  When the OFF position is selected, power is still supplied to the motor through the internal park switch. Both relays 1 and 2 are de-energized and the motor reverses its direction. When the motor reaches its park position, the park switch opens, removing motor power and releasing the brake solenoid which stops the motor.
 (2)  
When the wipers are turned on, friction of the wiper blade on the windshield moves the blade from its parked position parallel to the wiper arm to the wiping position at 20° to the arm. As the wiping position is reached, a spring-loaded unlatch mechanism on the arm locks to fix the blade in the wiping position. When the wipers are turned off, the arm sweeps into the parked position and a lever on the arm contacts the trip stud on the airplane. This unlatches the blade from the arm and allows the blade to pivot and assume the proper parked position.

 (3)  
When the wiper blade is in the parked position it should be free to move 1/8 to 1/4 inch from the stop by applying finger pressure. This takes up gear backlash.

 (4)  
A small spoiler is attached to the blade retaining clip to provide positive blade pressure for adequate wiping at high flight speeds. The blade retainer clip is fastened to the wiper arm and holds the blade tip to prevent lifting in flight when the system is not operating.

 B. Control
 (1)  To operate the windshield wipers, set the left and right WIPER control switches to the desired speed position, LO or HI. To stop the windshield wipers, set the control switches to OFF.
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747-400 MAINTENANCE MANUAL
 WINDSHIELD WIPER SYSTEM - ADJUSTMENT/TEST
_________________________________________
 1.  General
_______
 A.  This task is an operational test of the windshield wiper system. During this procedure you must apply water to the windshield. For the test you will make sure that the wipers operate at the LO and HI speeds and then move to the park position. The left and right windshield wipers operate independently. You can do a check of their operation separately or together.
 B.  There are no adjustments for the windshield wiper system in this procedure. For adjustment of the park position of the wiper arm, refer to AMM 30-42-02/401.
 TASK 30-42-00-715-001
 2.  Operational Test - Windshield Wiper System
__________________________________________
 A.  Standard Tools and Equipment
 (1)  Water spray - clean (to make windshield wet)
 B.  References
 (1)  
AMM 24-22-00/201, Manual Control

 (2)  
SSM 30-42-01

 (3)  
WDM 30-42-11

 C.  Access
 (1)  Location Zone 221 Control Cabin, LH - Outside No. 1 Left Window 222 Control Cabin, RH - Outside No. 1 Right Window
 D.  Preconditions
 S 865-008
 (1)  These conditions are necessary for this task:
 (a)  Electrical power on (AMM 24-22-00/201).
 E.  Procedure
 S 865-002
 (1)  Supply electrical power (AMM 24-22-00/201).
 S 645-003
 CAUTION: YOU MUST SUPPLY WATER TO THE WINDSHIELD BEFORE YOU OPERATE
_______ THE WIPERS. OPERATION OF THE WIPERS WITHOUT WATER CAN CAUSE DAMAGE TO THE WINDSHIELD.
 (2)  Apply a spray of clean water or windshield washer fluid to the windshield.
 NOTE: Continue to apply the water when the wiper is in motion.
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