Piper Navajo PA-31 Service Manual page 911

SECTION XIII
HEATING AND VENTILATING SYSTEM
13-1. INTRODUCTION. This section contains information for the operation, service and overhaul
of the
combustion heater and combustion air blower, used with the heater. The adjustment of the various
parts
will also be covered, along with the standard equipment used. There are modifications which have
been
made to the early 39D59 heaters and a B39D59 heater has been installed on later models. In order
to
distinguish between the systems, they will be called out as (39D59 heater system one), (39D59 heater
system two) or (B39D59 heater system). The 39D59 heater system two and B39D59 heater system
include
the addition of an override switch on the duct stat control and a combustion air blower switch added
to the
combustion air blower circuit.
13-2. DESCRIPTION AND PRINCIPLES OF OPERATION. The flow of air for heating and defrosting
is
taken through an inlet in the lower right side of the airplane nose section and directed to a Janitrol heater
located in the right side of the nose section. From the heater, air for defrosting is directed through outlets
located on the instrument panel cover, while air for cabin heat and fresh air is delivered through outlets
on
the forward cabin bulkhead and grills located in the cabin side panel next to the floor. These functions
are
controlled by a heater switch and control levers along the lower right side of the instrument panel.
The heater is protected from overheating by heat limit switch. If the heater temperature reaches a prede-
termined setting, the limit switch opens and the heater becomes inoperative. This is indicated by the illumina-
tion of the OVER TEMP warning light in the annunciator panel. The OVER TEMP light will stay on until the
.temperature drops below the predetermined limit. The heater can be reset using the START, R ES ET button
. under the heater switch after the OVER TEMP light goes out.
An additional scoop mounted on top of the airplane in the dorsal fin draws fresh air into the cabin
through individual vents over each seat. Each vent is adjustable for the desired airflow. A cabin exhaust
outlet is located in the raised floor panel of the aft cabin area. The exhaust scoop is located in
the lower,
center section of the fuselage, in line with the cabin door. This exhaust scoop is controlled by a push-pull
knob on the lower right side of the instrument panel. A ventilating fan for this outlet is available as optional
equipment. An optional heater hourmeter is available on S/N 31-8212001 and up. Field modification
instructions kit (764 304) for the hourmeter is available on S/N 31-2 to 31-8212001.
13-3. JANITROL HEATER.
13-4. TROUBLESHOOTING. Troubles peculiar to the heating and ventilating system are listed in Table
XIII-I at the end of this section, along with their probable cause and suggested remedies.
13-5. HEATER OPERATION. The 35,000 B.T.U. Janitrol heater is controlled by a three position switch
located on the lower right side of the instrument panel, labeled FAN, OFF and HEAT. The FAN position
will operate the vent blower only and may be used for cabin ventilation on the ground or windshield
defogging when heat is not desired. For heat, the heater switch must be turned to HEAT which will start
fuel flow and ignite the burner simultaneously.
The heater uses gasoline from either right fuel tank when the fuel crossfeed is off, and from all tanks
when the crossfeed is on.
The control levers along the bottom of the instrument panel control airflow and temperature. The
right lever regulates air flowing to the cockpit through the heater system and the second lever from the
right controls air flowing to the cabin area. The left lever is connected to an adjustable thermostat which
makes it possible to select a desired temperature of heated air and the second lever from the left is the
defroster control.
For the overhaul and complete disassembly of the heater and its components, refer to Paragraph 13-39
of this manual. A wiring diagram of the heater Electrical System Installation will be found in Section XI of
this manual.
Revised: 1/29/82
HEATING AND VENTILATING SYSTEM
5B5
PIPER NAVAJO SERVICE MANUAL