ACT 2 - FLSCU-3 Channel LS2 - Low Level Sensor No. 2 Failure

TASK 28-46-00-810-835-A
ACT 2 - FLSCU-3 Channel LS2 - Low Level Sensor No. 2 Failure

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.

1. Possible Causes

FLSCU 3 [47QJ]
aircraft wiring
C/B-ACT LOW LVL R [51QJ]
PROBE-FQI NO 2, ACT2 [66QT2]

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 12-11-28-650-003	Pressure Refuel with Automatic Control
AMM 28-25-00-869-001	Fuel Transfer
ASM 282803
AMM 28-42-24-000-001	Removal of the Fuel Quantity Probe of the ACT
AMM 28-42-24-400-001	Installation of the Fuel Quantity Probe of the ACT
ASM 284602
AMM 28-46-34-000-001	Removal of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 28-46-34-400-001	Installation of the Fuel-Level Sensing Control-Unit (FLSCU)

3. Fault Confirmation
Subtask 28-46-00-865-075-A ** ON A/C NOT FOR ALL

A. Table of the circuit breakers referred to in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	ACT LOW LVL R	51QJ	M29

Subtask 28-46-00-710-066-B ** ON A/C NOT FOR ALL

B. Test
FLSCU-3 (47QJ), CHAN LS2 - LO LVL SENSOR No. 2 (66QT2) Input To RELAY-PANEL (802VU) Fault Confirmation

NOTE: The FQIC does not do a BITE test of the FLSCU-3 or the related ACT FLSS sensors. There is no operational manual test for the ACT low level sensors.

NOTE: OPTIONAL TESTING:
If a PSD A320-3 Fuel Level Sensing System Test Set is available, all of the tank mounted components can be tested, and the FLSCU relay outputs simulated. Access to the system is gained by removing the FLSCU (one of three) and installing the PSD A320-3.

(1) Examine the FUEL System Display ACT 2 FQ, and make sure that it contains more than 250 kg (560 lb):
(a) Refuel the ACT 2 AMM 12-11-28-650-003 if necessary.

NOTE: This is to make sure that the low level sensor is wet.
The fuel quantity/level at which the low level sensor changes state/operates is approximately 80 kg (180 lb) with the aircraft in a level attitude.

(2) Disconnect the connector 4065VC-A from the RELAY-PANEL (802VU).
(3) Use a MULTIMETER - STANDARD, to do a test for continuity, at the connector 4065VC-A, between the pin C and an applicable ground. This test must show an open circuit. If the test shows continuity, do the fault isolation procedure in Para. 4.A.
(4) Defuel the ACT 2 AMM 28-25-00-869-001.

NOTE: This is to make sure that the low level sensor is dry.

(5) Use a multimeter, to do a test for continuity, at the connector 4065VC-A, between the pin C and an applicable ground. This test must show continuity.
(6) If the test results are:
(a) As specified in steps (3) thru (5):
1 No more Trouble-shooting steps of the FLSCU-3 (47QJ) Channel LS2 - Low Level Sensor No. 2 (66QT2) are necessary.
2 Connect the connector 4065VC-A to the RELAY-PANEL (802VU).
(b) Not as specified in steps (3) thru (5):

go to Para. 4. and do the fault isolation.

4. Fault Isolation
Subtask 28-46-00-810-084-B ** ON A/C NOT FOR ALL

A. Procedure
(1) Examine the C/B-ACT LO LVL R (51QJ) and make a note if it is open or closed.
(2) If the C/B 51QJ is closed:

go to Step (4).

(3) If the C/B 51QJ is open:
(a) Do a visual check of the items that follow and repair, if necessary:
1 C/B 51QJ.
2 FLSCU-3 (47QJ).
3 FLSCU-3 rack connector (47QJ-A).
(b) Close the C/B 51QJ.
(c) Do the test given in Para. 3.B.
(4) Interchange the FLSCU-3 (47QJ) with FLSCU-1 (7QJ) AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
(5) Do the test given in Para. 3.B.
(a) If the test is satisfactory:
1 Install the original FLSCU-1 in the FLSCU-1 position.
2 Replace the FLSCU 3 [47QJ] AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
(b) If the fault continues:

install the FLSCUs in their original positions AMM 28-46-34-000-001 and AMM 28-46-34-400-001.

(6) Get access to the PROBE-FQI NO 2, ACT2 (66QT2) connector at 803VU2 AMM 28-42-24-000-001.

NOTE: In this procedure the ACT LRUs and items are identified with their complete identification. However, all ACT LRUs have the same identification labels irrespective of whether they are installed in the ACT 1 or the ACT 2 position.

(7) Test Equipment

(a) If there is:

approved test equipment available, go to Step (8)
no approved test equipment available, go to Step (9).

(8) Do a resistance check ASM 284602 of the low level sensor (part of PROBE-FQI No 2 ACT 2 (66QT2) at the tank wall connector 66QT2-A (803VU2) between pins E and D.

NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.

(a) If the resistance is between 330 and 480 ohms:

go to Step (9).

(b) If the resistance is not between 330 and 480 ohms:

go to Step (16).

(9) Do a check of the aircraft wiring ASM 284602 and ASM 282803 between:

the FLSCU-3 rack connector AB, pin 9A and the ACT to tank break connector 7618VC2, pin 9 (sensor input line - H)
the FLSCU-3 rack connector AB, pin 9B and the ACT to tank break connector 7618VC2, pin 10 (sensor input line - L)
the ACT aircraft to tank break free connector 7618VC2-A, pin 9 and the tank unit free connector 66QT2-A, pin E (sensor input line - H)
the ACT aircraft to tank break free connector 7618VC2-A, pin 10 and the tank unit free connector 66QT2-A, pin D (sensor input line - L)
the FLSCU-3 rack connector AA, pin 9A and the ground point DC1 (ground I/P)
the FLSCU-3 rack connector AA, pin 10A and the RELAY-PANEL (802VU) free connector 4065VC-A, pin C (LS2 channel output line to RELAY-PNL 802VU).

(10) Repair all the unserviceable wiring and connectors.
(11) Do the test given in Para. 3.B.
(12) If the fault continues:

remove the FLSCU-3 (47QJ) AMM 28-46-34-000-001.

(13) Use a MULTIMETER - STANDARD, to do a test, to make sure that 28VDC is available at the FLSCU-3 (47QJ) rack connector AA, pin 1C.
(14) If the 28VDC is available:
(a) Install the FLSCU-3 (47QJ) AMM 28-46-34-400-001.
(b) Go to Step (16).
(15) If the 28VDC is not available:
(a) Do a check of and replace, if necessary, the C/B-ACT LOW LVL R [51QJ] .
(b) Do a check of the aircraft wiring ASM 284602:

between the C/B-ACT LO LVL RIGHT (51QJ) terminal 2 and the FLSCU-3 rack connector AA, pin 1C (28VDC supply line).

(c) Repair all the unserviceable wiring and connectors.
(d) Install the FLSCU-3 (47QJ) AMM 28-46-34-400-001.
(e) Do the test given in Para. 3.B.
(16) If the fault continues:

replace the PROBE-FQI NO 2, ACT2 [66QT2] AMM 28-42-24-000-001 and AMM 28-42-24-400-001.

[Rev.8 from Aug 2018] 2026.04.04 04:39:44 UTC