Environmental System Description And Principles Of Operation - Piper PA-44-180 SEMINOLE Maintenance Manual

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 is provided to assist in locating and correcting possible malfunctions in the heating
system.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
1E16
2 1 - 0 2 - 0 0
Page 21-01
Revised: May 15, 1989