(d)
Gradually increase the thumbwheel setting until the SWITCHED CLOSED light comes on.
(e)
Make sure the thumbwheel setting is within the limits for the temperature switch closing.
(f)
Make sure the APU DUCT OVHT IND LIGHT L6 on the P83 panel is on.
(g)
The EICAS shows the "APU DUCT LEAK" status message.
(h)
Slowly reduce the probe temperature until the "switch opened" indication appears.
(i)
Make sure the thumbwheel setting is within the limits for the temperature switch open setting.
(j)
Make sure the difference between the switch closed setting and switch open setting is greater than the deadband requirement.
(k)
Disconnect the probe from the thermal switch.
(l)
Push the APU DUCT OVERHEAT RESET SW S220 on the P83 panel.
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747-400 MAINTENANCE MANUAL
(m)
Make sure the APU DUCT OVERHEAT IND LIGHT L6 is off.
(n)
Remove the EICAS status message "APU DUCT LEAK" (AMM 45-10-00/201).
S 915-062
(11)
Repeat the Thermal Switch Set Temperature Test for thermal switches S970, S971, S972, S973, S974, S975, S976, S977, S978, S979, S980, S981, S982, S983, S1173, S1924, S984, S985, and S986 in sequence. Refer to AMM 26-19-01/401 for access of thermal switches.
S 865-121
(12)
Repeat the Thermal Switch Set Temperature Test for thermal switches S2207, S2208, S2209, S2210, S2211, S2212, and S2213. Refer to AMM 26-19-01/401 for access thermal switches.
H.
APU Duct Overheat APU Shutdown Check
S 865-071
(1) Close the following circuit breaker on the P6 Panel and attach a DO-NOT-OPEN tag:
(a) 6G06, BCU 1
S 865-072
(2)
Push the battery switch to "on" at the P5 panel.
S 865-069
(3)
Open the following circuit breaker on the P6 panel and attach a DO-NOT-CLOSE tag:
(a) 6K18, APU ALTERNATE CONT
S 865-070
(4) Open the following circuit breaker on the P83 panel and attach a DO-NOT-CLOSE tag:
(a) APU PRIME CONT
S 025-013
(5)
Remove the M7847 APU electrical control unit from the E8 equipment center (AMM 49-61-07/401).
S 865-073
(6)
Close the following circuit breaker on the P83 panel and attach a DO-NOT-OPEN tag:
(a) APU DUCT OVHT
S 485-014
(7)
Connect the ohmmeter between airplane ground and pin E7 on airplane wiring connector DM7847BA, and set the ohmmeter to R X 1.
(8)
Make sure the ohmmeter reads an open circuit.
S 215-015
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747-400 MAINTENANCE MANUAL
S 485-016
(9)
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