TM 1-1520-240-102-10-2 blower starts and purges the heater combustion cham-ber of any unburned fuel, while the remainder of thecircuit remains inactive because of a 10 to 15 secondtime-delay relay. After the time-delay relay is energized,the ignition assembly is powered and the master fuelsolenoid valve opens, allowing fuel to flow to the heaterfuel 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) arein the lower outboard corner of both the pilot and thecopilot instrument panels. The knobs are labeled PULLFOR COCKPIT AIR. Each knob controls a valve on theheater ducting which regulates the airflow to the cockpit.2-10-4. Air Control Handles.Two air control handles are mounted through a placardon the right side of the canted console. The placard islabeled AIR CONTROL PULL FOR ON with each handlelabeled COCKPIT DEFOG OR DEFROST and CABINAIR. By pulling the DEFOG or DEFROST handle, heateror ventilating air is directed to the cockpit nose enclosureducting. The airflow is directed to the transparent portionof the jettisonable doors and nose enclosure providingdefrosting as well as additional forward cockpit sectionheating. When the CABIN AIR handle is pulled, heatedor ventilating air flows through the ducting to the cabin.2-10-5. Cabin Heat Controls.Fourteen manually adjustable outlets are provided in thecabin for the comfort of the passengers.2-10-6. Heater Caution.NOTESince the HEATER HOT caution will not extin-guish until the temperature in the combustionchamber is below 177_C, it may take severalattempts at restarting the heater beforeHEATER 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 automatictemperature control circuit. If air temperature in the heat-er rises to 177_C, an overheat switch deenergizes theautomatic temperature controller relay, shuts off theheating system, except the blower, and activates the712 HEATER HOT, 714A HTR HOT caution. The heat-ing system will not operate until the blower has loweredthe heater temperature to normal and the HTR STARTswitch is pressed. Even though the temperature in thecombustion chamber has lowered, the 712 HEATERHOT, 714A HTR HOT caution will not extinguish until theHTR START switch is pressed.
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