Loss of the Leak Detection Loop of the APU

TASK 36-22-00-810-812-A
Loss of the Leak Detection Loop of the APU

1. Possible Causes

BMC-1 [1HA1]
wiring
sensing element
wiring from the connector AA/7B to the sensing element (12HF)
wiring from the sensing element (19HF) to the connector AA/8B

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 36-11-00-740-001	BITE Test of the BMC 1(2)
AMM 36-11-34-000-001	Removal of the BMC
AMM 36-11-34-400-001	Installation of the BMC
AMM 36-22-00-100-801	Clean the Overheat Detection System (OHDS) Connectors and Apply the Electrical Insulating Compound
ASM 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 36-22-00-710-062-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the BITE test of the BMC1 AMM 36-11-00-740-001.

4. Fault Isolation
Subtask 36-22-00-810-061-B ** ON A/C NOT FOR ALL

A. If the test gives the maintenance message:
APU LOOP INOP OR BMC IDENT CKT:

remove the BMC-1 [1HA1] AMM 36-11-34-000-001.
do a continuity check of the APU loop from pin AA/7B of the BMC1 to pin AA/8B of the BMC1 ASM 362201.

NOTE: This procedure is related to the loss of the APU-loop detection signal or to incorrect continuity of the loop.
The resistance of the loop must be less than 15 ohms at ambient temperature.
The BMC gives the maintenance message when the resistance of the loop is more than 75 ohms (discontinuity).
There is continuity when the resistance of the loop is less than 75 ohms.

(1) If there is continuity and the resistance of the loop is between 15 ohms and 75 ohms:

do a check for a ground signal at pin AA/9A of the BMC1.

(a) If there is no ground signal:

repair the wiring .
install the BMC-1 [1HA1] AMM 36-11-34-400-001.

(b) If there is a ground signal:

do a check and clean all the connections ASM 362201 to remove contamination and decrease the resistance of the loop AMM 36-22-00-100-801.

1 If the fault continues:

replace the BMC-1 [1HA1] AMM 36-11-34-400-001.

(2) If there is no continuity:

do a check of the wiring from pin AA/7B of the BMC1 to the cable (11HF) and from pin AA/8B of the BMC1 to the cable (20HF) ASM 362201.

(a) If there is no continuity:

repair the wiring .
install the BMC-1 [1HA1] AMM 36-11-34-400-001.

(b) If there is continuity:

do a visual inspection of the sensing elements on the APU loop.

1 If a sensing element is damaged:

replace the sensing element .
install the BMC-1 [1HA1] AMM 36-11-34-400-001.

2 If no sensing element is damaged:

do a continuity check of each sensing element, one after the other.

a If there is no continuity on a sensing element:

replace the sensing element AMM 36-22-17-000-001 and AMM 36-22-17-400-001.
install the BMC-1 [1HA1] AMM 36-11-34-400-001.

b If there is continuity on a sensing element:

do a check and repair the wiring from the connector AA/7B to the sensing element (12HF) ASM 362201.
do a check and repair the wiring from the sensing element (19HF) to the connector AA/8B ASM 362201.
install the BMC-1 [1HA1] AMM 36-11-34-400-001.

Subtask 36-22-00-710-063-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:34:03 UTC