Heating. Ventilating And Defrosting System - Piper Aircraft Corporation Seneca II PA-34-200T Pilot Operating Handbook

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PIPER AIRCRAFT CORPORATION
PA-34-200T, SENECA II
7.25 HEATING, VENTILATING AND DEFROSTING SYSTEM
SECTION7
DESCRIPTION AND OPERATION
Heated air for cabin heat and windshield defrosting is provided by a Janitrol combustion heater
located in the aft fuselage behind the cabin baggage compartment close-off (refer to Figure 7-23). Air from
the heater is ducted forward along the cabin floor to outlets at each seat and to the windshield area.
Operation of the combustion heater is controlled by a three-position switch located on the control
console (Figure 7-25) between the front seats and labeled FAN, OFF and HEATER. Airflow and
temperature are regulated by the two levers on the console. The right-hand lever regulates air intake and the
left-hand lever regulates cabin temperature. Cabin comfort can be maintained as desired through various
combinations of lever positions. Passengers have secondary control over heat output by individually
adjustable outlets at each seat location.
For cabin heat, the air intake lever on the heater control · console must be partially or fully open and
the three-position switch set to the HEATER position. This simultaneously starts fuel flow and ignites the
heater; and, during ground operation, it also activates the ventilation blower which is an integral part of the
combustion heater. With instant starting and no need for priming, heat should be felt within a few seconds.
When cabin air reaches the temperature selected on the cabin temperature lever, ignition of the heater
cycles automatically to maintain the selected temperature. Two safety switches activated by the intake
valve and located aft of the heater unit prevent both fan and heater operation when the air intake .lever is in
the closed position. A micro switch, which actuates when the landing gear is retracted, turns · off the
ventilation blower so that in flight the cabin air is circulated by ram air pressure only.
When the three-position switch is in the FAN position during ground operation, the ventilation fan
blows fresh air through the heater ductwork for cabin ventilation and windshield defogging when heat is
not desired. When the heater controls are used either for cabin heat or for ventilation, air is automatically
ducted to the windshield area for defrosting.
The flow of defroster air to the windshield area can be increased by the activation of a defroster fan.
The fan is controlled by a defroster switch located on the control console between the two front seats.
To introduce fresh, unheated air into the cabin during flight, the air intake should be open and the
heater off. Ram air enters the system and can be individually regulated at each floor outlet. Overhead
outlets also supply fresh air for cabin ventilation. The occupant of each seat can manually adjust an outlet
in the ceiling to regulate the flow of fresh air to that seat area. An optional fresh air blower may be installed
in the overhead ventilation system to provide additional fresh air flow during ground operation.
An overheat switch located in the heater unit acts as a safety device to render the heater inoperative if
a malfunction should occur. Should the switch deactivate the heater, the OVERHEAT light on the control
console will illuminate. The overheat switch is located on the forward outboard end of the heater vent
jacket. The red reset button on the heater shroud can be reached through the bulkhead· access panel in the
aft cabin close-out panel.
To prevent activation of the overheat switch upon normal heater shutdown during ground operation,
turn the three-position switch to FAN for two minutes with the air intake lever in the open position before
turning the switch to OFF. During flight, leave the air intake lever open for a minimum of fifteen seconds
after turning the switch to OFF.
The combustion heater uses fuel from the airplane fuel system. An electric fuel pump draws fuel from
the left tank at a rate of approximately one-half gallon per hour. Fuel used for heater operation should be
considered when planning for a flight.
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ISSUED: AUGUST 23, 1976
REVISED: MARCH 11, 1977
REPORT: VB-850
7-25