(2)
Connect alumel (green) lead to thermocouple probe larger terminal and chromel (white) lead to smaller terminal.
(3)
Place hot soldering iron on thermocouple probe.
WARNING: HEAT GUNS, SOLDERING GUNS AND SOLDERING IRONS ARE NOT EXPLOSION-PROOF. DO NOT USE WHERE FUEL OR FUEL VAPOR IS PRESENT (REF MM 20-10-171, MAINTENANCE PRACTICES).
NOTE: Thermocouple junction is located approximately at center of probe. Soldering iron should, therefore, be placed on probe at center to assure adequate heat transfer.
(4)
Observe exhaust gas temperature indicator for temperature rise.
(5)
If no rise in temperature is evidenced in step (4), proceed as follows:
(a)
If indicator pointer does not move, replace thermocouple probe.
(b)
If indicator pointer moves down scale, probe is functional but leads to probe terminals are connected in reverse.
(6)
Disconnect leads to thermocouple probe.
(7)
Install probe in engine. Refer to Exhaust Gas Temperature Thermocouple Probe -Removal/Installation.
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Jun 20/83 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-71-21 Page 501
APU INDICATING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. APU indicating system consists of the engine overspeed light and the engine elapsed time indicator. The overspeed light is located in the control cabin; the elapsed time indicator is located on the engine. (See figure 1.)
2. Overspeed Light
A. The overspeed light provides an indication when the APU engine has attained an overspeed condition. The light is amber in color and it is located on the forward overhead panel. (See figure 1.) The overspeed light is energized when the APU engine speed reaches 110 percent service speed. At this speed, the 110 percent switch actuates and closes the overspeed shutdown relay K2. When the relay is in closed position, the circuit is completed to the overspeed light.
B. The overspeed light is connected to the APU annunciator light and to the master caution lights. When the overspeed light is energized, the APU annunciator and the overspeed lights are energized. Refer to Master Caution and Warning Lights, 33-15-0. The overspeed light is tested by pressing the light, or it is tested by actuation of the master test switch.
3. Elapsed Time Indicator
A. The elapsed time indicator records the number of hours the APU engine has been operating. The indicator is basically an electric clock, enclosed in a hermetically sealed case. Total engine operating time is indicated by a digital counter that records the operating time in hours and tenths of hours. The indicator is shock mounted on the APU engine oil cooler. (See figure 1.)
B. The elapsed time indicator is connected to the 95 percent switch and begins recording when the engine reaches 95 percent service speed, thus actuating the switch. The indicator continues to record the time while the engine is operating at or above 95 percent service speed. The indicator circuit is protected by a circuit breaker (figure 1) against sudden surges of current. When the circuit breaker is open, it can be reset by pushing in the reset button.
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May 15/67 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-72-0 Page 1
G02622
APU Indicating System Component Location 500
49-72-0 Figure 1 May 15/68
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
ELAPSED TIME INDICATOR - REMOVAL/INSTALLATION
1. Prepare for Elapsed Time Indicator Removal
A. Position BATTERY SWITCH and APU START SWITCH to OFF and placard that APU maintenance is "in work."
B. Open the circuit breaker on M280 module-APU accessory unit on E3-3 electronic shelf.
C. Open APU compartment access door latches and open access door. Install door support rods.
D. Support lower shroud, open shroud latches, and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
2. Remove Elapsed Time Indicator
A. Disconnect electrical plug from indicator. (See figure 401.)
B. Loosen clamp attaching indicator to bracket on oil cooler; remove assembled indicator and shockmount.
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