Cessna 172N - Page 136

SECTION
7
AIRPLANE
&
SYSTEMS DESCRIPTIONS
CESSNA
MODEL 172N
CABIN AIR
control knobs
(see
figure
7-8).
For
cabin ventilation,
pull
the CABIN
AIR knob out.
To
raise
the
air
temperature,
pull
the
CABIN
HT
knob
ort approximately
t/4 to
L/2 inch
for
a
small amount
of cabin heat.
Additional
heat
is
available by
pulling
the
knob
out farther; ma:rimum
heat
is a'railable with the CABIN HT knob
pulled
out
and
the
CABIN
AIR
knob
pushed
full in. When
no
heat
is de-
sired in
the cabin,
the CABIN
HT
knob
is
pushed
full in.
Front
cabin heat and
ventilating
air
is supplied by
outlet
holes spaced
across
a cabin
manifold
just
forward of the
pilot's
and copilot's feet.
Rear
cabin
heat and
air
is
supplied
by
two ducts from
the manifold, one
extending
down
each
side
of
the
cabin
to an
outlet at the front door
post
at
floor
level.
Windshield
defrost
air
is also
supplied
by
a duct
leading
from
the
cabin
manifold.
Two knobs
control
sliding valves
in
the
defroster out-
let and
permit
regulation of
defroster
air{low.
Separate
adjustable
ventilators supply
additional
air; one near each
upper
corner
of
the
windshield supplies
air for the
pilot
and
copilot,
and
two
ventilators
are
available
for the
rear
cabin
area to supply air
to the
rear
seat
passengers.
PITOT-STATIC
SYSTE M
A N D IN
STR U
ME NI S
The
pitot-static
system
supplies
ram
air
pressure
to
the
airspeed
indicator
and
static
pressure
to the
airspeed indicator,
rate-of-climb
indicator
and altimeter.
The
system
is composed
of either an unheated
or heated pitot
tube
mounted
on the
lower surface of
the
left
wing, an
external
static
port,
on the lower left side of
the
forward
fuselage, and
the associated
plumbing
necessary to
connect
the instruments
to the
soulces.
The
heated
pitot
system consists
of a
heating element
in the
pitot
tube,
a
rocker-type
switch
labeled
PITOT
HT on the
lower
left
side
of the
instru-
ment
panel,
a
10-amp
circuit
breaker
on
the switch
and control
panel,
and
associated
wiring. When
the
pitot
heat
switch
is turned
on, the element
in
the
pitot
tube
is heated
electrically to maintain
proper
operation in
possi-
ble icing
conditions.
Pitot
heat
should
be
used
only as required.
A
static
pressure
alternate
source valve
may
be installed
adjacent to
the
throttle
for use
when the
external
static
source
is malfunctioning.
This
valve
supplies
static
pressure
from
inside
the cabin instead of the
external
static
port.
If erroneous
instrument
readings
are
suspected
due to
water or ice
in the
pressure
line
going
to
the
standard
external
static
pressure
source.
7 -30