Inspect APU alternator belt
For easier access remove bottom cover inspect belt make sure its not broken and it's not too loose if broken inspect AC compressor & alternator pulleys , Make sure they rotate freely and not jammed, and aligned properly keep in mind if belt is broken, its usually due to two reasons: 1) Natural wear and tear 2) Jammed or misaligned pully To get the right belt open upper panel and check the label on the right for manufacturing date and serial number Then check label on alternator to determine if your alternator is 120 or 60 Amps.