Inspection/Check of the Thermocouple Probe (APS 3200)

TASK 49-72-15-200-003-A
Inspection/Check of the Thermocouple Probe (APS 3200)

WARNING: DO NOT TOUCH THE APU UNTIL IT IS SUFFICIENTLY COOL TO PREVENT BURNS WHEN YOU DO THE MAINTENANCE TASK(S).

1. Reason for the Job
Self explanatory
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	ACCESS PLATFORM 4M (13 FT)-ADJUSTABLE
No specific	1	MEGOHMMETER 100 MOHMS - MEASURING VOLTAGE 45 VDC
No specific	1	OHMMETER MULTIRANGE
No specific	AR	SAFETY CLIP - CIRCUIT BREAKER
No specific	AR	WARNING NOTICE(S)
No specific	Torque wrench: range to between 56 and 51 lbf.in (0.63 and 0.58 m.daN )

B. Work Zones and Access Panels

ZONE/ACCESS	ZONE DESCRIPTION
315AL, 316AR

C. Referenced Information

REFERENCE	DESIGNATION
TASK 24-42-00-861-001-A	Energize the Ground Service Network from the External Power
TASK 24-42-00-862-001-A	De-energize the Ground Service Network Supplied from the External Power
TASK 29-00-00-864-001-A	Put the Related Hydraulic System in the Depressurized Configuration before Maintenance Action
TASK 49-72-15-000-001-A	Removal of the Thermocouple (APS 3200)
TASK 49-72-15-400-002-A	Installation of the Thermocouple (APS 3200)
TASK 52-41-00-010-001-A	Open the APU Doors for Access
TASK 52-41-00-410-001-A	Close the APU Doors after Access
Thermocouples

3. Job Set-up
Subtask 49-72-15-860-065-A ** ON A/C NOT FOR ALL

A. Aircraft Maintenance Configuration
(1) Energize the ground service network
(Ref. AMM TASK 24-42-00-861-001).
(2) On panel 25VU, make sure that the APU MASTER SW pushbutton switch is off.
(3) Put a WARNING NOTICE(S) in position in the cockpit to tell persons not to start the APU.
(4) Make sure that the ground fire-extinguishing equipment is available.
(5) Make sure that the hydraulic systems are depressurized (Ref. AMM TASK 29-00-00-864-001).

Subtask 49-72-15-865-069-A ** ON A/C NOT FOR ALL

B. Open, safety and tag this(these) circuit breaker(s):

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	APU/APU/CTL	2KD	L42
121VU	APU/ECB/SPLY	1KD	L41

Subtask 49-72-15-010-057-A ** ON A/C NOT FOR ALL

C. Get Access
(1) Put an ACCESS PLATFORM 4M (13 FT)-ADJUSTABLE in position below APU access doors 315AL and 316AR.
(2) Open APU access doors 315AL and 316AR (Ref. AMM TASK 52-41-00-010-001).
(3) Set the LIGHT control SW 11LJ to the ON position.

4. Procedure
Subtask 49-72-15-210-052-A ** ON A/C NOT FOR ALL

CAUTION: -YOU MUST NOT INCREASE THE TIGHTENING TORQUE MORE THAN THE MAXIMUM VALUE.

APPLY ALL TIGHTENING TORQUES WITH A TORQUE WRENCH OR A CALIBRATED SCREWDRIVER.

A. Inspection/Check of the Thermocouple Probe

NOTE: There are two thermocouples. The procedure is the same for each of them. Long thermocouple TC1 P30 (1) is installed on the right side of the APU and short thermocouple TC2 P31 (2) is installed on the left side of the APU.

(1) Disconnect long thermocouple TC1 P30 (1) or short thermocouple TC2 P31 (2) from the mount bracket.
(2) Remove the bolt (3) and disconnect long thermocouple TC1 P30 (1) or short thermocouple TC2 P31 (2) from the exhaust.
(3) Do a visual check of the thermocouple probe and make sure that:

There are no cracks.
The thermocouple probe is not bent.
There are not kinks.
There is no erosion on the tip of the thermocouple probe.

(a) If you find damage on the thermocouple probe, replace the related thermocouple (1) or (2) (Ref. AMM TASK 49-72-15-000-001) and (Ref. AMM TASK 49-72-15-400-002).
(4) Do an insulation resistance test at ambient temperature:
(a) Connect a MEGOHMMETER 100 MOHMS - MEASURING VOLTAGE 45 VDC to measure the resistance between:

Positive pin (pin 1) of the thermocouple connector and the switch assembly housing.
Negative pin (pin 2) of the thermocouple connector and the switch assembly housing.

(b) Make sure that the minimum resistance value is 100 megohms after 60 seconds.
(c) If the resistance value is less than 100 megohms after 60 seconds, replace the related thermocouple (1) or (2) (Ref. AMM TASK 49-72-15-000-001) and (Ref. AMM TASK 49-72-15-400-002).
(5) Do a continuity resistance test:
(a) Connect an OHMMETER MULTIRANGE between the positive pin (pin 1) and the negative pin (pin 2) of the thermocouple connector.
(b) Make sure that the resistance is between 0.7 and 3 ohms.
(c) If the resistance value is not in the specified limits, replace the related thermocouple (1) or (2) (Ref. AMM TASK 49-72-15-000-001) and (Ref. AMM TASK 49-72-15-400-002).
(6) Connect long thermocouple TC1 P30 (1) or short thermocouple TC2 P31 (2) to the exhaust with the bolt (3).
(7) TORQUE the bolt (3) to between 56 and 51 lbf.in (0.63 and 0.58 m.daN )

.
(8) Connect long thermocouple TC1 P30 (1) or short thermocouple TC2 P31 (2) to the mount bracket.

5. Close-up
Subtask 49-72-15-410-055-A ** ON A/C NOT FOR ALL

A. Close Access
(1) Make sure that the work area is clean and clear of tools and other items.
(2) Set the LIGHT control SW 11LJ to the OFF position.
(3) Close APU access doors 315AL and 316AR (Ref. AMM TASK 52-41-00-410-001).
(4) Remove the access platform(s).

Subtask 49-72-15-865-070-A ** ON A/C NOT FOR ALL

B. Remove the safety clip(s) and the tag(s) and close this(these) circuit breaker(s):

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	APU/APU/CTL	2KD	L42
121VU	APU/ECB/SPLY	1KD	L41

Subtask 49-72-15-860-068-A ** ON A/C NOT FOR ALL

C. Aircraft Maintenance Configuration
(1) De-energize the ground service network
(Ref. AMM TASK 24-42-00-862-001).
(2) Remove the WARNING NOTICE(S).

[Rev.10 from 2021] 2026.04.01 01:32:09 UTC