The modulating valves maintain a controlled flow
of bleed air to the leading edge distribution
system, and they are controlled by pneumatic
thermostats. The complete system is monitored
for hot spots by heat-sensing switches.
Before flight, the deicing manifold system may
be tested for leakage. This leak testis performed
by pressurizing the system: OPEN the No. 4
engine bleed-air valve; the Nos. 1, 2, and 3 engine
bleed-air valves remain CLOSED, and both
fuselage shutoff valves are in the OPEN position.
When the bleed-air pressure on the bleed-air
manifold reads 70 psi, the No. 4 engine bleed-air
valve is closed and the leak test switch is actuated.
As the bleed-air pressure drops, the time-delay
relay will illuminate the ACCEPT light after an
8-second delay if the system is tight. The light will
go out when the test switch is released.
The involvement of the AME2 and AMEC in
the maintenance of the deicing system normally
consists of troubleshooting. To troubleshoot
intelligently, you must be familiar with the system.
In addition, you must know the function of each
component in the system and have a mental
picture of the location of each component in
relation to other components in the system. This
can be achieved by studying the schematic
diagrams of the system.
As an aid, the aircraft manufacturer furnishes
troubleshooting charts, which give recommended
procedures to follow during troubleshooting.
Figure 3-5 shows a deicing system overheat
warning troubleshooting chart. This chart lists the
most probable cause first and then branches to
the next most probable cause. By following the
recommended charts and procedures, you can
save many valuable maintenance hours.
RAIN REMOVAL SYSTEM
The rain removal system shown in figure 3-6
controls windshield icing and removes rain by
directing a flow of heated air over the windshield.
This heated air serves two purposes. First, the air
breaks the rain drops into small particles, which
are then blown away. Secondly, the air heats the
windshield to prevent the moisture from freezing
Figure 3-5.-Deicing troubleshooting chart.