During a recent maintenance event, a customer complained of poor cabin cooling on the ground while the APU was in operation.
One of the first steps to effectively troubleshoot poor cooling of the aircraft while on the ground is to inspect the overall cleanliness of the Primary and Secondary Heat Exchangers of the Engine Control Unit (ECU). A quick assessment of the upper surface of the heat exchanger can be performed within minutes by opening the ram air inlet door located on the left side of the ram air inlet duct. Debris and blockage of the cooling fin surfaces will degrade the efficiency of the ECU and can lead to poor cooling performance.
There are procedures in place in the maintenance manual for the 750, 800, 800XP, 850XP, 900XP and 1000 series aircraft to clean the heat exchanger in place as the first step in troubleshooting this complaint.
In this case, we discovered a bird’s nest in the secondary heat exchanger as the cause for inefficient cabin cooling. After removing the nest, the aircraft departed with a crew pleased with the results.
For more information about this service bulletin or other technical issues, contact your Duncan Aviation Hawker Tech Rep.
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