2-16. OPERATING THE AUXILIARY POWER UNIT (APU)
a. Bleed Fuel System (Initial Start-Up).
(1) Remove the fuel return line located in floor of APU
compartment. Place the fuel return line in a suitable
(2) Operate the priming lever on the fuel transfer pump
until bubbles cease to appear in the fuel.
(3) Connect the fuel return line.
If the fuel pump lobe on the camshaft is up, crank
the engine one revolution to permit hand priming.
When finished, return the priming lever to the
disengaged (inward) position.
b. Starting. Check the engine to make sure the fuel system has
been bled and it has been filled with oil. if necessary, prime
the fuel system as described above.
(1) When starting a cold engine in ambient temperatures
above 55° , preheat with GENERATOR PREHEAT
switch for 20 seconds.
Low temperatures may require longer preheating. If
engine fails to start quickly, allow 30 seconds for
starter to cool. Apply preheat for 1 minute, and
repeat starting procedures.
(2) Continue to hold GEN. PREHEAT switch.
(3) Press the GENERATOR START/STOP switch to
(4) Release the GENERATOR START/STOP switch
after the engine starts and reaches speed.
If oil pressure does not reach operating pressure,
stop engine immediately and troubleshoot. Failure
to heed this caution can result in damage to APU
(5) Check oil pressure on gauge mounted on APU. Oil
pressure should read approximately 20 psi.