Fleet Type: All

Applicable Reference:AMM 26-18-00

Discrepancy: Wing to body overheat light illuminates

Possible Fix: Use Wing to body tester to troubleshoot system (C26007-1. This
tester works far better than the alternate methods of troubleshooting
covered in the AMM
Tip: Install the test prior to opening and access panels to effected system.

A normal loop voltage is from 5-6 volts ac, and wing to body light alerts
occurs around 2 volts. If you find a loop that has low voltage, open access
to loops and watch for the voltage to increase. If the voltage increases
look in the area just opened for bleed leaks or overheated duct/elements.

If voltage does not increase, troubleshoot per normal procedure of spliting
loops and looking for voltage increase to identify which element is faulty.

Reason/Explanation:
The use of a standard DMM of testing the system is acceptable as long as the
sensing elements are not within 100 degrees F of their temperature set
point, and the test is of short duration. Boeing discourages the use of a
DMM because repeated usage of DMM over time could potentially have negative
impact to the sensors.

The test box allows you to use the actual aircraft system and it’s actual
condition to troubleshoot. This procedure provides a high level of success
in troubleshooting system discrepancys.

Thanks to Tom S. for his input.

> FOR INFORMATION ONLY. UNCONTROLLED DATA !.