Cessna 402C - Page 247

G-.~'402C
MOOEL
HEATING AND DEFROSTING
SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
7-43
During heating and/or defrosting operation, cabin recirculated air or
ram air from the fuselage nose air inlet is directed to the heater and
heated, then flows to the pilot and passenger compartments. A cabin com-
partment air outlet ;s provided to exhaust cabin air.
The cabin heater depends upon the aircraft fuel system for its fuel sup-
ply. Fuel pressure is supplied by a fuel pump mounted on the heater assem-
bly; the main fuel system auxiliary fuel pumps need not be turned on for
proper heater operation.
On the ground. the cabin overhead air system can be used for additional I
ventilation by placing the optional auxiliary cabin ventilation blower
switch in the ON position. The fan provides unheated fresh air to the
cabin through tlte overhead directional air vent outlets. In fl ight, the
blower becomes inoperative and the heating system can be used for ventila-
tion by placing the cabin heat switch to the OFF position, pulling out the
cabin air knobs and opening the heat outlets as desired.
CABIN HEAT SWITCH
The
cabin heater is controlled by a two-position cabin heat switch, see
Figure 7-18. Switch positions are ON and OFF. Placing the switch in the
ON position starts and maintains heater operation and turns the cabin fan
on low.
AUXILIARY CABIN VENTILATION BLOWER SWITCH (OPTIONAL)
The auxiliary cabin ventilation blower is controlled by a two-position
blower switch on the instrument panel. Switch positions are CABIN VENT FAN
and OFF. Placing the switch in CABIN VENT FAN position operates the venti-
lation blower on the ground to furnish fresh air to overhead directional
air vents.
CABIN FAN SWITCH
The
cabin fan is controlled by a three-position switch, see Figure 7-18.,
Switch positions are HI, OFF and LO. Placing the switch in the HI position
operates the cabin fan at high speed, or if the cabin heat switch is on,
the heater blower will operate at high speed rather than its normal low
speed.
CABIN AIR TEMPERATURE CONTROL KNOB
The cabin air temperature is controlled by the cabin heat knob, see Fig-
ure 7-1. Clockwise rotation of this knob increases the desired tempera-
ture.
This knob adjusts a thennostat, which in turn control s heated air tem-
perature in a duct located just aft of the heater. ~hen the temperature of
the heated air exceeds the setting of the thennostat, the thennostat auto-
matically opens and shuts off the heater. When the heated air cools to the
thermostat setting, the heater starts again. Thus the heater cycles on and
off to maintain an even air temperature.
The heater al so will be cycled by a thennoswitch in the cabin air duct,
which shuts off the heater when the duct temperature reaches approximately
104.4°C (220°F). When the duct temperature drops to a nonnal operating
level, the heater will restart automatically. The action of this switch is
independent of the cabin thennostat setting and is not adjustable irt
flight.
1 November 1979
Revision 4 - 1 December 1983