Section VII. UTILITY SYSTEMS
2-51. DEFROSTING SYSTEM.
Description. The defrosting system is an integral
part of the heating and ventilation system. The system
consists of two warm air outlets connected by ducts to the
heating system. One outlet is just below the pilot's
windshield and the other is below the copilot's windshield.
A push-pull control, placarded DEFROST AIR, on the
windshield. When pulled out, defrosting air is ducted to
the windshield. As the control is pushed in, there is a
corresponding decrease in airflow.
1. Vent blower switches - As required.
2. Cabin temperature mode selector switch
3. Cabin temperature control rheostat - As
4. Cabin air, copilot air, pilot air, and defrost air
controls - As required.
c Manual Operation
1. Pilot air, copilot air - IN.
2. Cabin air and defrost air controls - Out
3. Cabin temperature mode selector switch
- MAN HEAT.
4. Cold air outlets - As required.
5. Manual temperature switch - As required.
Manual Operation. If the automatic temperature
control should fail to operate, the temperature (of defrost
air and cabin air) may be controlled manually by
manipulating the CABIN TEMP MODE control switch
between the OFF and MAN HEAT positions. This control
is located on the overhead control panel (fig. 2-12).
2-52. SURFACE DEICING SYSTEM.
Description. Ice accumulation is removed from
each inboard and outboard wing leading edge, and both
horizontal stabilizers by the flexing of deicer boots which
are pneumatically actuated. Engine bleed air, from the
engine compressor, is used to supply air pressure to
inflate the deicer boots, and to supply vacuum, through
the ejector system, for boot hold down during flight. A
pressure regulator protects the system from over inflation.
When the system is not in operation, a distributor valve
applies vacuum to the boots for hold down.
Operation of the surface de-ice
system in ambient temperatures
below -40°C can cause permanent
damage to the de-ice boots.
De-ice boots are intended to remove ice
after it has formed rather than prevent its formation. For
the most effective deicing operation, allow at least 1/2
inch of ice to form on the boots before attempting ice
removal. Very thin ice may crack and cling to the boots
instead of shedding.
Never cycle the system rapidly, this
may cause the ice to accumulate
outside the contour of the inflated
boots and prevent ice removal.
A three position switch on the overhead
control panel placarded SURF DEICE MANUAL OFF
SINGLE CYCLE AUTO, controls the deicing operation.
The switch is spring loaded to return to the OFF position
from SINGLE CYCLE AUTO or MANUAL. When the
SINGLE CYCLE AUTO position is selected, the distributor
valve opens to inflate the wing boots. After an inflation
period of approximately 6 seconds, an electronic timer
switches the distributor to deflate the wing boots and a 4
second inflation begins in the horizontal stabilizer boots.
When these boots have inflated and deflated, the cycle is
If the switch is held in the MANUAL
position, the boots will inflate simultaneously and remain
inflated until the switch is released. The switch will return
to the OFF position when released. After the cycle, the
boots will remain in the vacuum hold down condition until
again actuated by the switch.