APU EGT Indicating System Component Location
Figure 1 (Sheet 1)

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 49-71-00
 ú CONFIG 2 ú 01 Page 2 ú Mar 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
SEE D
SEE C
C
ETC
THERMOCOUPLE
PROBE

PROPORTIONAL CONTROL VALVE (PCV)
D

APU EGT Indicating System Component Location
Figure 1 (Sheet 2)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH THE ETC ú

 49-71-00
 ú CONFIG 2 ú 01 Page 3 ú Nov 15/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////

APU SHROUD
(AFT CARGO COMPARTMENT)
APU EGT Indicating System Schematic
Figure 2

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 49-71-00
 ú CONFIG 2 ú 01 Page 4 ú Mar 15/92
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B.  The temperature difference between the ETC thermocouple probes (hot junction) and the EGT indicator (cold junction) makes the electrical signals in the circuit for the EGT indicating system. The difference between these electrical signals is in proportion to the difference in temperature between the ETC thermocouple probes and the EGT indicator. Because the electrical signals only correspond to a temperature difference, the ambient temperature of the control cabin must be added to the temperature difference to get the actual temperature of the exhaust gases. The temperature of the control cabin has small variations. The EGT indicator has a bimetal (thermostatic) spring to make allowances for these temperature changes. The EGT indicator does show the correct temperature for the exhaust gases in all ambient conditions.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH THE ETC ú

 49-71-00
 ú CONFIG 2 ú 01 Page 5 ú Mar 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
EXHAUST GAS TEMPERATURE INDICATING SYSTEM - ADJUSTMENT/TEST
___________________________________________________________
 1.  General
_______
 A.  This procedure gives the tasks to do the two tests of the exhaust gas temperature (EGT) indicating system. The two tests are the insulation resistance test and the functional test of the EGT resistor. You can do these tests independently or together.
 B.  On the APU engine, the electrical leads are chromel and alumel. The alumel lead is green, negative and magnetic. The chromel lead is white, positive and not magnetic. In the fuselage, the electrical leads are copper and constantan. The copper lead is positive and red. The constantan lead is negative and yellow.
 C.  The EGT resistor is installed in the flight deck directly below the right No. 3 window. To change the circuit resistance, you move the constantan lead from terminal to terminal on the coarse adjustment and vernier adjustment. The increment of resistance between two coarse adjustments is 0.15 ohms. The increment of resistance between two vernier adjustments is 0.05 ohms. The external circuit resistance is 13.50 ohms. This external resistance does not include the EGT indicator and the APU harness. To decrease the circuit resistance more than the range of the coarse and vernier adjustments, you make a shorter resistance spool. To increase the circuit resistance more than the range of the coarse and vernier adjustments, you use a spare or new resistance spool.
 TASK 49-71-00-705-025
 2.  AIRPLANES WITH THE ETC; Insulation Resistance Test
__________________________
 A.  Standard Tools and Equipment
 (1) Ohmmeter - approved to 100,000 ohms
 B.  Access
　
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