21-Cont./Effec. Page 21-5 Revised: February 28, 2002
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GENERAL.
Instructions for maintaining the cabin vent and heating systems are contained in this chapter. Also incorporated in this chapter are instructions for the inspection and operation of the 45,000 BTU heater unit, defroster, and ventilation system.
DESCRIPTION AND PRINCIPLES OF OPERATION.
Vent air can be supplied through the heater unit, and by ram air or fan through the upper vent ducts. Air is supplied to the upper vent system by way of an inlet on the leading edge of the vertical stabilizer or through the inlet located on the left side of the aft fuselage, depending on serial number.
Heated air for the cabin and defroster operation is obtained from the combustion heater located in the nose section of the airplane. Fresh air is supplied to the heater from an intake located in the nose and routed through the heater and into the cabin through six adjustable outlets. Operation of the heater is controlled by a three-position switch located on the lower right side of instrument panel and labeled FAN, OFF and HEATER. The FAN position will operate the ventilation blower of the heater and may be used for cabin ventilation or windshield defogging on the ground when heat is not desired. For additional defrost capability adjust cabin temperature control and then adjust the three-position switch to HEATER.
For cabin heat, the air intake lever located on the lower right side of the instrument panel must be partially or fully open and the three-position switch set to HEATER. This will start the fuel flow and ignite the burner simultaneously. With instant starting and no need for priming, heat should be felt within a few seconds. There are two safety switches installed at the intake valve located forward of the heater unit which are activated by the intake valve and wired to prevent both fan and heater operation unless the air intake valve is moved off the closed position.
Regulating the heater and airflow is accomplished by adjusting the levers on the instrument panel. The lower lever regulates the defrosters, while the center lever regulates the intake valve and the top lever regulates the cabin temperature. Cabin temperature and air circulation can be varied to suit individual requirements by various combinations of lever settings.
Heat may be supplied before starting the engines by turning on the master switch, opening the air intake valve and placing the heater switch in the HEATER position.
An overheat limit switch is located in the aft outboard end of the heater vent jacket, which acts as a safety device to render the heater inoperative if a malfunction should occur. A red reset button on the switch can be reached through the nose. Operation of this switch results in illumination of the overheat light located on the lower right side of the instrument panel, or a “HTR OVER TEMP” lamp located in the annunciator panel lights, upper center panel. To prevent activation of the overheat limit switch upon normal heater shutdown during ground operation, turn the switch to the FAN position for two minutes, while leaving the air intake lever in the open position, before turning the switch to the OFF position.
There are four overhead fresh air vents which are supplied by a separate inlet in the dorsal fin or through the inlet located on the left side of the aft fuselage, depending on serial number. The system can be supplemented by an optional blower.
TROUBLESHOOTING.
A troubleshooting chart (Chart No. 2101) is provided to assist in locating and correcting possible malfunctions in the heating system.
21-00-00 Page 21-7 Revised: February 28, 2002
CHART 2101. TROUBLESHOOTING (JANITROL HEATER)
Trouble Cause Remedy
Heater fails to light. Heater switch or circuit breaker off. Turn on heater switch or close circuit breaker.
Low voltage supply. Apply external power supply. Attempt to start heater.
Fuel cut off from tank. Turn on heater switch.
Regulator not operating — Note — Check for low pressure or replace regulator.
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