Trouble Shooting; Removal, Installation And Repair; Ventilating System - Cessna 1969-1976 172 Series Service Manual

14-7. DEFROSTER SYSTEM.
14-8. DESCRIPTION. The defrosting system is
comprised of
a
duct a c r o s s the aft side of the fire-
wall, defroster outlets, mounted on the left and
right sides of the cowl deck immediately aft of the
windshield and flexible ducting connecting the system.
14-9. OPERATION. Air from the duct a c r o s s the
a f t side of the firewall flows through flexible ducts
to the defroster outlets. The temperature and volume
of this air is controlled by the settings of the heater
system control.
14-10. TROUBLE SHOOTING. Since the defrosting
system depends on proper operation of the heating
system, refer to paragraph 14-5 for trouble shooting
the heating and defrosting systems.
14-11. REMOVAL, INSTALLATION AND REPAIR.
Figure 14-1 may be used as a guide for removal,
installation and r e p a i r of defrosting system compo-
nents. Cut hose to length and install in the original
routing. T r i m hose winding shorter than the hose
to allow clamps to be fitted. A defective defroster
outlet must be repaired or replaced.
14-12. VENTILATING SYSTEM.
14-13. DESCRIPTION. The ventilating system is
comprised of two airscoops mounted in the inboard
leading edge of each wing, a manually-adjustable
ventilator installed on each side of the cabin near the
upper c o r n e r s of the windshield, two plenum cham-
b e r s mounted i n the rear cabin wing root areas, a
f r e s h airscoop door on the right side of the fuselage
just forward of the copilot's seat,
a
control knob on
the instrument panel and flexible ducting connecting
the system.
14-14. OPERATION. A i r received from scoops
mounted i n the inboard leading edges of the wings is
ducted t o adjustable ventilators mounted on each side
of the cabin near the upper c o r n e r s of the windshield.
R e a r seat ventilation is provided by plenum chambers
mounted in the left and right
rear
cabin wing root
a r e a s . These plenum chambers receive r a m air f r o m
the airscoops in the inboard leading edges of the
wings. Each plenum chamber is equipped with a
valve which m e t e r s the incoming cabin ventilation air.
This provides a chamber of expansion of cabin air
which greatly reduces inlet
air
noise. F i l t e r s a t the
air inlets a r e primarily noise reduction filters. F o r -
ward cabin ventilation is provided by
a
f r e s h airscoop
door mounted on the right side of the fuselage, just
forward of the copilot seat. The scoop door is opera-
ted by a control in the instrument panel marked "CAB-
IN AIR.
''
F r e s h air from the scoop door is routed t o
the duct a c r o s s the aft side of the firewall, where it
is distributed into the cabin. A s long as the "CABIN
HEAT" control is pushed in, no heated air can enter
the firewall duct; therefore, when the "CABIN AIR"
control is pulled out, only f r e s h air f r o m the scoop
will flow through the duct into the cabin. A s the "CAB-
IN HEAT" control is gradually pulled out, more and
more heated
air
will blend with the f r e s h air f r o m the
scoop and be distributed into the cabin. Either one,
or both of the controls may be s e t a t any position
f r o m full open t o full closed.
14-15. TROUBLE SHOOTING. Most of the opera-
tional troubles i n the ventilating system are caused
by sticking
or binding of the inlet scoop door or its
control. Check the airscoop filter elements i n the
wing leading edges for obstructions. The elements
may be removed and cleaned or replaced. Since air
passing through the f i l t e r s
is
emitted into the cabin,
do not use
a
cleaning solution which would contam-
inate the air. The f i l t e r s may be removed to in-
crease air flow. However, their removal will cause
a
slight increase in noise level.
14-16. REMOVAL, INSTALLATION AND REPAIR.
Figure 14-2 may be used as a guide for removal, in-
stallation and r e p a i r of the ventilating system com-
ponents. A defective ventilator or scoop must be r e -
paired or replaced. Check for proper operation of
ventilating controls
after installation or repair.
SHOP NOTES:
14-4