o
Now reassemble
the
APU
air
cleaner
using
reverse
order
of
disassembly.
c. The inspection of fuel lines and fittings for leakage, restrictions,
or other damage is the third of the preliminary checks to be made.
As
mentioned earlier, the APU stores the fuel supply in the main fuel cells.
Submerged fuel pumps located in the lower fuel cells pump the fuel to a fuel
distribution terminal.
Connect the fuel supply line between the fuel
distribution terminal and the fuel inlet tee connection mounted in the
bulkhead of the cargo compartment and connect to the APU fuel pumps. The
APU fuel pumps then pump the fuel to the APU primary fuel filter.
Inspection of fuel lines and fittings for leakage, restrictions, or damages
begin at the point where the fuel inlet hose connects to the inlet side of
the APU fuel pump. The absence of fuel at the inlet side of the fuel pump
indicates a problem exists between the fuel supply source and the inlet side
of the APU fuel pump. If the fuel is flowing to the inlet side of the APU
fuel pump and not through to the pump outlet, then fuel pump operation is
suspect. When fuel is flowing through to the fuel pump outlet port and not
through to the primary fuel filter inlet connection, the fuel line between
the pump outlet and primary fuel filter inlet connection is suspect. Refer
to Figure 8 for a fuel flow illustration.
d. The checks for the APU engine fuel supply system covered in the
previous steps address the fuel supply system from the fuel cells to the
inlet fitting of the primary fuel filter. The APU fuel filter system check
is the final preliminary step taken when the APU engine cranks but fails to
start.
Gain access to the fuel filters through the APU side compartment
door. Mount the filters on the rear bulkhead of the APU compartment. To
remove contaminants from the primary and secondary fuel filters, you must
use the following steps:
o
The MASTER switch and the APU FUEL SHUT OFF switch must be set to
the ON position.
o
Drain the primary fuel filter and then the secondary APU fuel
filter by opening the drain cocks (Item 1, Figure 9). Be sure to
place a container at the end of the filter drain hoses (Item 3,
Figure 9) to collect the drained contaminants and fuel.
o
When fuel fails to flow from the secondary fuel filter quick-
disconnect coupling half (Item 3, Figure 9), a clogged fuel
filtering system is suspect, change the primary (Item 4, Figure
9) and secondary (Item 5, Figure 9) fuel filter elements. Refer
to
10
OD1702
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