HEADQUARTERS OH-58A, Technical Manual

Page: 85 / 292

TM 55-1520-228-10
2-48. A COMBUSTION HEATER.
a. Description . A combustion heater is installed on
the electrical shelf behind the passenger seat, on
helicopter serial Nos. 70-15263 thru 70-15278, in the aft
equipment compartment. Fuel for heater operation is
supplied by the helicopter fuel system and routed
through the heater fuel filter, pump, relief valve, and
shutoff valve. Ignition is supplied by a heater mounted
ignition assembly which converts 28 volts DC to high
voltage, producing a continuous spark during heater
operation. Air is supplied by a blower through a port on
the right side of the helicopter and routed to the
combustion chamber. Heater exhaust gasses are piped
overboard through a shrouded exhaust flue. Heated air
is distributed by a heater mounted ventilating air blower
and routed through ducts to the forward and aft cabin
compartments. Two adjustable distribution valves are
provided in the pilot compartment and two fixed
openings for the passenger compartment. Controls for
heater starting are located on the overhead panel and
two controls are mounted on the vertical column on pilot
seat back. The left side control is for temperature and
the right side control operates the heater shutoff valve in
the event of fumes, fire, or heater malfunction. A heater
fail light is mounted on the console and will indicate
heater malfunction. Consumption of fuel is 3.5 gallons
per hour for 30,000 BTU heater and 4.5 gallons per hour
for the 50,000 BTU heater. (Refer to figure 2-16.)
b. Combustion Heater Pre-Start Check.
(1) FUEL PUMP circuit breaker - In.
(2) HTR PWR circuit breaker - In.
(3) HTR CONT circuit breaker - In.
(4) FIREWALL SHUT-OFF CONTROL-- In.
(5) BAT switch - BAT.
(6) FUEL VALVE - ON
(7) HEAT-OFF-VENT switch - OFF.
c. Normal Operation.
(1) HEAT-OFF-VENT switch ON. Check that
combustion air and vent blowers operate and HEATER
FAIL caution light is on.
(2) HTR START switch Press and hold, Ignition
should occur within 5 to 10 seconds HEATER FAIL
caution light should go off.
(3) TEMP CONT knob Regulate for desired
temperature.
(4) HEAT-OFF-VENT switch OFF, to shut down
heater.
NOTE
HEAT-OFF-VENT switch in OFF
position, the combustion air and vent
blowers will continue to operate,
cooling and purging the heater, and
will cut off automatically when the
heater has cooled if manual cooling
and purging is desired place switch
in VENT position, then return switch
to OFF.
d. Emergency Shutdown.
(1) FIREWALL SHUT-OFF CONTROL knob
-
Release and pull out.
(2) HEAT-OFF-VENT switch
-
OFF.
2-39