Description; Operation - Cessna 1969-1976 172 Series Service Manual

SECTION 14
UTILITY SYSTEMS
TABLE OF CONTENTS
UTILITY SYSTEMS
. . . . . . . . . . . .
Heating System
. . . . . . . . . . . .
Description
. . . . . . . . . . . .
Operation
. . . . . . . . . . . .
Trouble Shooting
. . . . . . . . .
Description
. . . . . . . . . . . .
Removal, Installation and Repair
. .
Defroster System
. . . . . . . . . .
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14-1. UTILITY SYSTEMS.
14-2. HEATING SYSTEM.
14-3. DESCRIPTION.
The heating system is com-
prised of the heat exchange section of the exhaust
muffler, a shut-off valve, mounted on the right f o r -
ward side of the firewall a push-pull control on the
instrument panel, outlets and flexible ducting con-
necting the system.
14-4. OPERATION. Ram a i r is ducted through a n
engine baffle inlet and heat exchange section of the
exhaust muffler, to the shut-off valve at the firewall.
The heated air flows from the shut-off valve into a
duct a c r o s s the aft side of the firewall, where it is
distributed into the cabin. The shut-off valve, oper-
ated by
a
push-pull control marked "CABIN HEAT,
''
located on the instrument panel, regulates the volume
of heated air entering the system. Pulling the con-
trol full out supplies maximum flow, and pushing
control in gradually decreases flow, shutting off flow
completely when the control is pushed full in.
14-5. TROUBLE SHOOTING. Most of the operation-
al troubles in the heating, defrosting and ventilating
systems a r e caused by sticking o r binding air valves
and/or their controls, damaged air ducting, or de-
fects in the exhaust muffler. In most cases, valves
o r controls can be f r e e d by proper lubrication.
Operation
. . . . . . . . . . . .
Removal, Installation and Repair
.
e
Trouble Shooting
. . . . . . . . .
Ventilating System
. . . . . . . . . .
Description
. . . . . . . . . . . .
Operation
. . . . . . . . . . . .
Trouble Shooting
. . . . . . . . .
Removal, Installation and Repair
.
.
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Damaged o r broken p a r t s must be repaired
or re-
placed. When checking controls, ensure valves
respond freely to control movement, that they move
in the c o r r e c t direction, and that they move through
their range of travel and seal properly. Check that
hose a r e properly secured, and replace hose that are
burned, frayed o r crushed. If fumes
are
detected
in the cabin,
a
thorough inspection of the exhaust
system should- be accomplished. Refer to applicable
paragraph in Section 11 for this inspection. Since
any holes o r cracks may permit exhaust fumes to
enter the cabin, replacement of defective p a r t s is
imperative because fumes constitute a n extreme
danger. Seal any gaps in shut-off valves a t the f i r e -
wall with Pro-Seal
#700
(Coast Pro-Seal Co., Los
Angeles, California) compound, or equivalent com-
pound.
14-6. REMOVAL, INSTALLATION AND WPAIR.
Figure 14-1 illustrates the heating and defrosting
systems, and may be used as a guide during removal,
installation and repair of heating system components.
Burned, frayed or crushed hose must be replaced
with new hose, cut t o length and installed in the orig-
inal routing. T r i m hose winding shorter than the
hose t o allow clamps t o be fitted. Defective air
valves must be repaired
or
replaced. Check for
proper operation of valves and their controls after
repair o r replacement.
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