APU puzzle in C-130 Technical Posted April 8, 2010 APU came from overhaul, ran through test cell - all good. Installed on aircraft, bleed air on, but no load, there is a 5 - 10psi pressure surge, small EGT and RPM flux. When a load is applied (eg aircon pack), it stabilizes. Removed and sent to test cell, again nothing could be found. Installed on another aircraft, has the same problem. Replaced the load control valve, but still the same. Anyone have any ideas ...??