Message Name:

SHORT CIRCUIT

Message Code:

B3-007407

Associated CAS:

PACK LOOP FAIL
(Caution)

BLEED LOOP FAULT
(Advisory)

The PACK LOOP A is detected shorted to ground by the IASC-1 during the system self-test. Check the loop and wiring isolation to ground.

• Pack Duct
• Bleed Loop Routing
• Pack Loop Sensor 1A (MT73)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• Bleed Loop Routing and Visual Aid Guide
• Troubleshooting Guide for Bleed Loops
• Pack Channel A Bleed Loop Information
• If the bleed loop resistance value is within limits try cleaning the bleed loop connections per SPM 51-25-00-110-801 and then reapply lubrication to the connections per SPM 20-20-00. Lubrication part number is called out in each bleed loop installation procedure. Run the aircraft after the cleaning and applying lubing procedure and see if the BLEED LOOP FAULT clears.

1. Gain access to IASC #1 through the LH aft nose kidney panel 141BL.
2. Disconnect connector A55P4 from the IASC and check resistance between pins 10 and 11 MT73. Resistance should be approximately 15.8 Ω.
3. Isolate a system short through standard practices by isolating the loop and wiring from the IASC. Repair faulty wire segment or replace loop as required.

NOTE: Measure Insulation resistance and line resistance of the detection loops as per the Leak Detection Elements Troubleshooting Sheet. Make sure line resistance & insulation values are within the specified limits.

Pack Channel A Bleed Loop Information

The test will identify if the pack loop has a short or open. Perform resistance checks on the applicable loop per AMM 36-21-00-760-801

NOTE: Before replacing a loop always look at the loop for routing, ensure loop is not too close to the plumbing or the bleed hole on a valve. Review AMM 36-21-00-992-801 for component location. See individual loops for specific routing information.

If the one or both of the pack Leak Detection Element (LDE) do not meet the resistance checks then replace the LDE.

NOTE: Often while troubleshooting this discrepancy the CAS is not usually present. However what you may find is higher than normal resistance such as 10 Ω or higher above nominal. It is not high enough to trip a bleed loop fault CAS message but high enough to assist in troubleshooting. When you get the resistance value down to nominal values then it is safe to say you've corrected the discrepancy.