We have 2 GTCP85-180 APU's with two different issues.
1. This APU will not accelerate to full speed at all. You hit start and the starter turns the engine and combustion is occurring but doesn't go past about maybe 10% and stays there until I hit the off switch. I checked if there were any loose air lines and there were none. Any ideas? Bad starter? Broken FCU shaft?
2. This second APU just shuts down after maybe about 5 minutes of operating. No loads on it at all, it just dies. Could it be that fuel solenoid on the FCU or maybe the centrifugal switch? Is there any way to test what it could be without just swapping parts?
