(2) Fresh air outlets. Fresh air is ducted
after heater shutdown to purge heat from the system.
directly from the fresh air plenum to individual outlets in
This switch will shut off the ventilation blower when the
duct temperature is reduced to 52 C.
the cockpit and cabin positioned in the ceiling above the
seats. Airflow volume is controlled at each outlet. The
direction of airflow is controlled by moving the outlet in it
(9) Heater cycling switch. A cycling switch
located in the hot air plenum disconnects power to the
heater fuel solenoid valve at 107C. If this automatic
(3) Stale air exhaust system. Stale air
function should fail, temperature within the plenum will
exhausted from the cabin area though the exhaust
ultimately exceed 149C and cause a 7.5-ampere fuse to
plenum in the cabin ceiling and is ducted to two vents
blow, shutting down the heater. The 7.5-ampere fuse,
located in the cabin on each side of the fuselage.
which is in series with the HTR control switch and the
TEMP CONTROL circuit breaker, cannot be replaced in
(4) Push-pull cockpit ventilation control. Two
flight due to its location.
push-pull type air inlet controls, placarded VENT AIR -
PUSH ON, are located below the pilot and copilot
(10) Heater control switch. A switch placarded
subpanels to manually regulate cockpit ventilation.
HEATER OFF AUTO, located on the right subpanel,
When pushed IN, either control will cause outside airflow
controls cabin heater operation. Either mode, AUTO or
from outlets above the respective rudder pedals As a
MAN, will activate the combustion air blower, the
control is pulled out, there is a corresponding decrease
ventilation blower (if aircraft is on the ground), the heater
in the amount of air flow.
fuel pump, open the fuel solenoid valve; and deliver
power to the igniter for combustion. AUTO position of
(5) Push-pull cabin ventilation control.
the heater control switch activates the cabin heater
push-pull type control, placarded CABIN AIR, located on
system and couples it with a temperature-regulation
the fight subpanel (fig. 2-7, manually controls ventilation
circuit, which maintains cabin heat between 18C and
of the cabin. Airflow is at maximum when the control is
29C, as established by the temperature control
pushed in. As the control is pulled out there is a
thermostat. MAN position activates the cabin heater
corresponding decrease in the amount of airflow.
system but cuts out the temperature-regulation circuit
allowing the heater to operate continuously until limit
(6) Heater combustion unit. The heater is a
switches within the hot air plenum cuts it off at either
combustion unit that uses the same fuels as the engines.
107C or 149C.
The heater is located in the lower right m-d of the nose
avionics compartment. Air for combustion is ducted from
(11) Temperature control circuit breakers. The
the nose avionics compartment to a combustion blower
which forces air into the combustion chamber. Taking
and all sensing and regulating circuits are protected by a
air from the nose avionics compartment helps to cool the
single 2-ampere circuit breaker, placarded TEMP
compartment by absorbing heat from installed electronic
CONTROL, located on the copilot's circuit breaker and
equipment. The combustion blower operates on the
ground whenever electrical power is applied.
(12) Cabin temperature rheostat. A rheostat,
(7) Heater fuel pump. A heater fuel pump in
placarded CABIN TEMP, located on the right subpanel,
the left wing outboard of the fuselage, forward of the
controls cabin temperature between 18C and 29C in
main wing spar, operates whenever the heater control
the AUTO mode of cabin heater operation.
switch is ON. Fuel for the heater is obtained from the
(13) Cabin heat out indicator light.
continue to operate until all fuel is consumed from the
press-to-test light, placarded CABIN HEAT OUT located
left nacelle tank.
on the copilot's instrument panel, illuminates if the cabin
heater is inoperative (heater control switch ON or at
(8) Pressure differential switch and duct
AUTO and cabin temperature lower than 18C).
temperature thermal switch. When either combustion
blower air flow or vent blower airflow is insufficient, a
b. Normal Operation - Cabin Heat.
differential pressure switch prevents heater operation.
Also, to prevent heat damage to equipment located
adjacent to a heater outlet, a duct temperature thermal
switch allows the ventilation blower to continue operation
Operation with GPU is the same as
on the ground
operation with aircraft power.
Change 10 2-55