APU AUTO SHUTDOWN - NO ACCELERATION, Main Start-Contactor Fault (131-9(A))

TASK 49-00-81-810-831-A
APU AUTO SHUTDOWN - NO ACCELERATION, Main Start-Contactor Fault (131-9(A))

1. Possible Causes

MAIN START CONTACTOR SHOWS OPEN CIRCUIT
damage or contamination of electrical connection STRT MTR (+)
electrical connections
aircraft wiring
damage and contamination of electrical connection STRT MTR (+)

2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	AR	MULTIMETER - STANDARD

B. Referenced Information

REFERENCE	DESIGNATION
AMM 49-00-00-860-008	APU Start by External Power
ASM 494201
AMM 49-42-51-400-006	Installation of the Starter Motor (131-9(A))

3. Fault Confirmation
Subtask 49-00-81-710-150-A ** ON A/C NOT FOR ALL

A. Read-out of ECB Trouble-Shooting Data
(1) Put the APU MASTER SW to the ON position.

NOTE: Make sure that the A/C batteries are switched ON!

(2) Get access to the APU SHUTDOWN report.
(3) Push the '>' adjacent to LRU DATA:

the MCDU menu shows
MAIN START CONTACTOR SHOWS OPEN CIRCUIT

(4) Start the APU and apply Bleed Air for 20 seconds, minimum AMM 49-00-00-860-008.

4. Fault Isolation
Subtask 49-00-81-810-108-A ** ON A/C NOT FOR ALL

A. If an APU auto shutdown occurs during the APU operation and the APU SHUTDOWN report gives the maintenance message:

NO ACCELERATION
ACFT BAT NOT SELECTED/CONTACTOR (5KA)

related to Fault Code Number (FCN) 123

Do a check for damage or contamination of electrical connection STRT MTR (+) of the STARTER MOTOR (8KA).

(1) Make sure that the electrical connections are correctly connected AMM 49-42-51-400-006.
(2) If electrical connection STRT MTR (+) is damaged or has contamination:

Repair or clean as necessary.

(3) If the electrical connection is correct:

Use a MULTIMETER - STANDARD to do a resistance check of the aircraft wiring between electrical connection STRT MTR (+) and ECB (59KD) AB/10J.

(a) If the resistance value is not between 9 kOhms and 11 kOhms:

Replace the aircraft wiring.

(b) If the resistance value is in the specified limits:

Do a check and repair the aircraft wiring from
MAIN-START CONTACTOR (5KA) B/5 to APU MASTER SW P/BSW (14KD) A/D1
and
MAIN-START CONTACTOR (5KA) B/3 to ECB (59KD) AC/1
and
MAIN-START CONTACTOR (5KA) A/D to BACK-UP-START CONTACTOR (10KA) A/F
and
ECB (59KD) AB/10J to electrical connection STRT MTR (+) of the STARTER MOTOR (8KA)
ASM 494201.

Subtask 49-00-81-810-108-B ** ON A/C NOT FOR ALL

Do a check for damage and contamination of electrical connection STRT MTR (+) of the STARTER MOTOR (8KA).

(1) Make sure that the electrical connections are correctly connected AMM 49-42-51-400-006.
(2) If electrical connection STRT MTR (+) is damaged or has contamination:

Repair or clean as necessary.

(3) If the electrical connection is correct:

Use a MULTIMETER - STANDARD to do a resistance check of the aircraft wiring between electrical connection STRT MTR (+) and ECB (59KD) AB/10J.

(a) If the resistance value is not between 9 kOhms and 11 kOhms:

Replace the aircraft wiring.

(b) If the resistance value is in the specified limits:

Do a check and repair the aircraft wiring from
MAIN-START CONTACTOR (5KA) B/5 to APU MASTER SW P/BSW (14KD) A/D1
and
MAIN-START CONTACTOR (5KA) B/3 to ECB (59KD) AC/1
and
ECB (59KD) AB/10J to electrical connection STRT MTR (+) of the STARTER MOTOR (8KA)
ASM 494201.

Subtask 49-00-81-710-151-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:40:39 UTC