blower starts and purges the heater combustion cham-
ber of any unburned fuel, while the remainder of the
circuit remains inactive because of a 10 to 15 second
time-delay relay. After the time-delay relay is energized,
the ignition assembly is powered and the master fuel
solenoid valve opens, allowing fuel to flow to the heater
fuel control unit to complete the start.
2-10-3. Cockpit Air Knob.
Two cockpit air knobs (15, fig 2-1-7 and 9, fig. 2-1-9) are
in the lower outboard corner of both the pilot and the
copilot instrument panels. The knobs are labeled PULL
FOR COCKPIT AIR. Each knob controls a valve on the
heater ducting which regulates the airflow to the cockpit.
2-10-4. Air Control Handles.
Two air control handles are mounted through a placard
on the right side of the canted console. The placard is
labeled AIR CONTROL PULL FOR ON with each handle
labeled COCKPIT DEFOG OR DEFROST and CABIN
AIR. By pulling the DEFOG or DEFROST handle, heater
or ventilating air is directed to the cockpit nose enclosure
ducting. The airflow is directed to the transparent portion
of the jettisonable doors and nose enclosure providing
defrosting as well as additional forward cockpit section
heating. When the CABIN AIR handle is pulled, heated
or ventilating air flows through the ducting to the cabin.
2-10-5. Cabin Heat Controls.
Fourteen manually adjustable outlets are provided in the
cabin for the comfort of the passengers.
2-10-6. Heater Caution.
Since the HEATER HOT caution will not extin-
guish until the temperature in the combustion
chamber is below 177_C, it may take several
attempts at restarting the heater before
HEATER HOT caution extinguishes.
A heater caution capsule labeled 712 HEATER HOT,
714A HTR HOT is on the master caution panel (fig.
2-14-6). This caution indicates failure of the automatic
temperature control circuit. If air temperature in the heat-
er rises to 177_C, an overheat switch deenergizes the
automatic temperature controller relay, shuts off the
heating system, except the blower, and activates the
712 HEATER HOT, 714A HTR HOT caution. The heat-
ing system will not operate until the blower has lowered
the heater temperature to normal and the HTR START
switch is pressed. Even though the temperature in the
combustion chamber has lowered, the 712 HEATER
HOT, 714A HTR HOT caution will not extinguish until the
HTR START switch is pressed.