S 494-028
(2) For hydraulic systems No. 2 and No. 3, do this task: Wing Landing Gear Door Locks Installation (AMM 32-00-30/201).
(3) S 644-013Lubricate the new packing (5) and the threads of the jamnut (4) with hydraulic fluid.
(4) S 434-014Remove the cap from the transmitter (2).
(5) S 424-015Put the transmitter (2) in the bracket.
(6) S 434-029Install the washer (6), the packing (5), and the jamnut (4).
(7) S 764-016Do a check of the electrical resistance between the case of the transmitter (2) and the airplane structure (AMM 20-22-01/601).
NOTE: The resistance must be less than 0.0025 ohms.
S 434-017
(8)
Remove the cap from the hydraulic tube (1).
S 434-018
(9)
Connect the hydraulic tube (1) to the snubber (3).
S 434-019
(10)
Connect the electrical connector (7) to the transmitter (2).
S 864-020
(11)
Remove the DO-NOT-CLOSE tag and close the circuit breaker for the applicable hydraulic system:
(a)
P415 Main Power Distribution Panel 1) 415K37 HYD PRESS IND SYS 1 2) 415K38 HYD PRESS IND SYS 2 3) 415K39 HYD PRESS IND SYS 3
(b)
P414 Main Power Distribution Panel 1) 414G23 HYD 4 PRESS IND
S 864-021
(12) Pressurize the applicable hydraulic system (AMM 29-11-00/201).
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747-400 MAINTENANCE MANUAL
S 794-022
(13)
Examine the transmitter (2) for leakage.
(a)
If you find leakage, repair the cause of the leakage.
S 714-023
(14)
Make sure the hydraulic pressure indication, on the EICAS MAINT PAGES for 29 HYD, is between 2800-3200 psi.
S 864-024
(15)
Release the pressure in the hydraulic system if it is not necessary (AMM 29-11-00/201).
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747-400 MAINTENANCE MANUAL
HYDRAULIC FLUID OVERHEAT WARNING SYSTEM - DESCRIPTION AND OPERATION
___________________________________________________________________
General
_______
A. The hydraulic fluid overheat warning system gives a visual warning if the temperature of any of the hydraulic systems becomes too high. The system also shows the actual value of the temperature of each hydraulic system.
B. The system has four hydraulic fluid temperature transmitters. It uses the hydraulic control module to give a warning of a hydraulic fluid overheat condition. It uses the EICAS HYD synoptic page to show the temperature of each system.
Hydraulic Fluid Temperature Transmitter (Fig. 1)
_______________________________________
A. The hydraulic fluid temperature transmitters are installed on the case drain modules near the aft side of the hydraulic system reservoirs.
B. The transmitters measure the temperature of the case drain fluid that comes from the hydraulic pumps. The transmitters send an ac signal that changes in proportion to the fluid temperature. Electrical power for the transmitters is supplied by the 28 volt ac power bus.
Operation (Fig. 2)
_________
A. Functional Description
(1)
The temperature transmitters send temperature signals to the hydraulic interface module (HYDIM). The HYDIM sends the signals to the EICAS interface unit (EIU) and the hydraulic control module. The EIU then sends the signals to the EICAS HYD synoptic page and the central maintenance computer system (CMCS). The EICAS HYD synoptic page shows system temperature in degrees celsius (°C) as digital displays.
(2)
The amber SYS FAULT light on the hydraulic control module will go on if the temperature of the total case drain flow from the engine-driven pump, demand pump, and auxiliary pump increases above 105 °C. This overheat condition will cause advisory and status messages to come into view. HYD OVHT SYS 1,2,3, or 4 will be shown on the EICAS display. The status message will be shown when the STAT key is pushed in.
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