APU Loop Inoperative

TASK 36-12-00-810-808-A
APU Loop Inoperative

1. Possible Causes

wiring
BMC-1 [1HA1]
SENSING ELEMENT-OVERHEAT,WING [11HF]
OVHT SENS ELEMENT [12HF]
OVHT SENS ELEMENT [13HF]
OVHT SENS ELEMENT [14HF]
OVHT SENS ELEMENT [15HF]
OVHT SENS ELEMENT [16HF]
OVHT SENS ELEMENT [17HF]
OVHT SENS ELEMENT [18HF]
OVHT SENS ELEMENT [19HF]
CABLE ASSY [20HF]

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

REFERENCE	QTY	DESIGNATION
9240SI	1	CONTROLLER-LOOP

B. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 36-22-00-810-879-A	APU Leak Detection
ESPM 204422
AMM 36-11-00-740-802	BITE Test of the Engine Bleed Air System (EBAS) (System Test)
AMM 36-11-34-000-001	Removal of the BMC
AMM 36-11-34-400-001	Installation of the BMC
AMM 36-22-00-100-803	Clean the Overheat Detection System (OHDS) Connectors and Apply the Electrical Insulating Compound
ASM 362201
AWM 362201
AMM 36-22-17-000-001	Removal of the APU Overheat Sensing-Elements
AMM 36-22-17-400-001	Installation of the APU Overheat Sensing-Elements

3. Fault Confirmation
Subtask 36-12-00-710-060-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the BITE test of the EBAS AMM 36-11-00-740-802.

4. Fault Isolation
Subtask 36-12-00-810-065-B ** ON A/C NOT FOR ALL

A. If the test gives one of these maintenance messages:

APU LOOP OPEN
APU LOOP INOP OPEN
or
APU LOOP INOP SHORT.

NOTE: This procedure is applicable when there is a loss of the APU loop detection-signal or to the incorrect continuity of the loop.

Remove BMC-1 AMM 36-11-34-000-001.
On shelf 95VU, connect the 9240SI CONTROLLER-LOOP between BMC-1 pin AA/4C and AA/5C ASM 362201.
Do a check of the continuity resistance shown on the 9240SI CONTROLLER-LOOP:

(1) If the continuity resistance value is less than 16 Ohms:

On shelf 95VU, connect the 9240SI CONTROLLER-LOOP between connector BMC-1 pin AA/6E and the ground ASM 362201.
Do a check of the insulation resistance shown on the 9240SI CONTROLLER-LOOP.

(a) If the insulation resistance is more than 10 kOhms:

Go to Para. 4.B.

(b) If the insulation resistance is less than 10 kOhms:

Do the fault isolation steps (Ref. TSM TASK 36-22-00-810-879).

(2) If the continuity resistance value is more than 16 Ohms

Connect the 9240SI CONTROLLER-LOOP between connector 1969VC pin A/19 to A/20 AWM 362201.

(a) If the continuity resistance value is more than 16 Ohms:

Do a visual inspection of the sensing elements and the connecting cables on the APU loop.

1 If a sensing element or a connecting cable is damaged:

Disconnect the 9240SI CONTROLLER-LOOP from connector 1969VC pin A/19 to A/20.
Replace the defective sensing element or connecting cable AMM 36-22-17-000-001 and AMM 36-22-17-400-001.
Install BMC-1 AMM 36-11-34-400-001.

2 If no sensing element or connecting cable is damaged:

Go to Para. 4.B.

(b) If the continuity resistance value is less than 16 Ohms:

Connect the 9240SI CONTROLLER-LOOP between connector 1969VC pin A/19 and BMC-1 pin AA/4C AWM 362201.

1 If the continuity resistance value is more than 16 Ohms:

Disconnect the 9240SI CONTROLLER-LOOP from connector 1969VC pin A/19 and BMC-1 pin AA/4C.
Repair or replace the wiring ESPM 204422.
Install BMC-1 AMM 36-11-34-400-001.

2 If the continuity resistance value is less than 16 Ohms:

Connect the 9240SI CONTROLLER-LOOP between connector 1969VC pin A/20 and BMC-1 pin AA/5C AWM 362201.

a If the continuity resistance value is more than 16 Ohms:

Repair or replace the wiring ESPM 204422.
Install BMC-1 AMM 36-11-34-400-001.

b If the continuity resistance value is less than 16 Ohms:

Do the cleaning procedure AMM 36-22-00-100-803.
Do the BITE test of the EBAS AMM 36-11-00-740-802.
* If the fault continues:
** Replace BMC-1 [1HA1] AMM 36-11-34-000-001 and AMM 36-11-34-400-001.

Subtask 36-12-00-810-074-A ** ON A/C NOT FOR ALL

B. Dichotomy Procedure

NOTE: The purpose of this procedure is to find and isolate the elements that causes a high continuity resistance on the leak detection loop of the APU.

(1) Do a check of the continuity resistance shown on the 9240SI CONTROLLER-LOOP:
(a) If the continuity resistance value is more than 16 Ohms:

Disconnect the connecting cable (11HF) of connector 1969VC pin A/19 and the connecting cable (20HF) of the connector 1969VC pin A/20. Disconnect one after the other all the sensing elements between the connection cables (11HF) and (20HF) AMM 36-22-17-000-001.
Measure the continuity resistance with the 9240SI CONTROLLER-LOOP between the center pin on the two ends of each of the elements.
Do a check of the continuity resistance shown on the 9240SI CONTROLLER-LOOP:

1 If the continuity resistance value is more than 16 Ohms:

Disconnect the 9240SI CONTROLLER-LOOP.
Replace the defective elements:
SENSING ELEMENT-OVERHEAT,WING [11HF] or
OVHT SENS ELEMENT [12HF] or
OVHT SENS ELEMENT [13HF] or
OVHT SENS ELEMENT [14HF] or
OVHT SENS ELEMENT [15HF] or
OVHT SENS ELEMENT [16HF] or
OVHT SENS ELEMENT [17HF] or
OVHT SENS ELEMENT [18HF] or
OVHT SENS ELEMENT [19HF] or
CABLE ASSY [20HF]
AMM 36-22-17-000-001 and AMM 36-22-17-400-001.
Install BMC-1 AMM 36-11-34-400-001.

2 If the continuity resistance value is less than 16 Ohms:

Disconnect the 9240SI CONTROLLER-LOOP.
Clean all the connections of the sensing elements and the connecting cables to remove contamination and decrease the resistance of the loop AMM 36-22-00-100-803 AWM 362201.
Connect again all the sensing elements or connecting cables disconnected AMM 36-22-17-400-001.
Install BMC-1 AMM 36-11-34-400-001.

(b) If the continuity resistance value is less than 16 Ohms:

Disconnect the 9240SI CONTROLLER-LOOP.
Connect again all the sensing elements or connecting cables disconnected AMM 36-22-17-400-001.
Replace BMC-1 [1HA1] AMM 36-11-34-000-001 and AMM 36-11-34-400-001.

[Rev.8 from Aug 2018] 2026.04.04 04:34:00 UTC