APU OVERTEMP
(Warning)

During the start sequence or while the APU is in operation, the temperature of the EGT sensor has increased higher than the over temperature limit for two seconds or more. The FADEC will cause an APU automatic shut-down if the aircraft is Weight on Wheels (WonW). In Flight the APU will continue to run, but the same CAS message will remain.

• Blockage in the Auxiliary Power Unit (APU) Inlet Door
• Blockage in the Auxiliary Power Unit (APU) Inlet Duct Forward Section
• Load Control Valve (LCV)
• Auxiliary Power Unit (APU) Engine Branched Wiring Harness
• Surge Control Valve (SCV)
• EGT Sensors, both (#1 and #2)
• Auxiliary Power Unit (APU) FADEC Controlling Sensors
• Full-Authority Digital Engine-Controller (FADEC)
• Fuel Control Unit (FCU)
• Auxiliary Power Unit (APU)

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

APU EGT exceeds a Schedule limit which is a function of APU speed, P2, T2 and operating conditions (ECS and MES). In this condition the APU will auto shutdown on the ground only.

Note: Make sure the APU OVERSPEED or OVERTEMP is not the result of De-Ice / Anti-Ice fluid ingestion while the APU was in operation.

WARNING: DE-ICE/ANTI-ICE FLUIDS ARE FLAMMABLE AND VERY CORROSIVE. INGESTION OF THESE FLUIDS IN AN OPERATING APU MAY CAUSE APU DAMAGE AND INJURY TO PERSONNEL SERVICING THE AIRCRAFT.

1. Ensure the Load Control valve is closed.Swap or replace as necessary and do the close out.
2. Ensure no blockage exists in APU Inlet. Remove blockage and do the close out.
3. Examine the inlet-duct forward section for blockage using a boroscope. Remove blockage and do the close out
4. Examine the parts of the APU that move as follows:

   1. Loosen one of the cover bolts that hold the hand-crank access cover on the starter motor.
   2. Remove the other cover bolt.
   3. Turn the hand-crank access cover to get access to the 0.25-inch square recession on the end of the starter motor.
   4. Use the tool on the 0.25-inch square recession to turn the APU internal parts.
   5. Listen for unusual noises in the APU while you turn the internal parts. Are there unusual noises?
   6. Replace APU and do the close out.

5. Disconnect the MPE1P1 connector from the LVC (MPE1) and do a check for continuity between pins A and B on the LVC (MPE1) receptacle. Continuity should be between 65 to 85 ohms. Replace LCV as necessary and do the close out.
6. Disconnect the A3P1 connector from the FCU (A3) and do a check for continuity between pins C and D on the FCU (A3) receptacle. Continuity should be between 30 to 38 ohms. Replace FCU as necessary and do the close out.
7. Perform wiring checks between P802 at the APU firewall interface (FS1046 LHS) and MPE1P1 (LCV). Replace the Engine Branched Wiring-Harness and do close out.
8. Perform wiring checks between P802 and FCU (A3P1) Replace the Engine Branched Wiring-Harness and do close out.
9. Perform wiring checks between P802 and the FADEC (A108AP1). Repair or replace the defective interface wiring. Do the close out.
10. Perform wiring checks between J802 (AC wiring harness) and A108AP1 (FADEC). Repair or replace the defective interface wiring and do the close out.
11. Swap or replace FADEC.
12. Do the close out.
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