TM 5-4520-240-14
6F (l.1 to 7.8C). Replace the thermostat if it does
to the side of the groove toward the point of the needle
not perform as described.
and press the preformed packing into the adhesive.
After the adhesive sets, coat the preformed packing
(4) Test the fuel heater for proper operation. Con-
nect the two heater leads to a source of 28-volt dc
and the needle groove with Aircraft Grease, fuel and oil
resistant per Military Specification G27617, or
power. Replace the heater if it does not heat.
equivalent, and install the assembled needle and
(5) Test the solenoid coil for continuity between
preformed packing in the carburetor. Tighten the ad-
the insulated lead and the braided ground lead.
Replace the coil if it is open, if the coil insulation is
justment needle gently until it just bottoms in the car-
buretor, then back it out two full turns to provide a
damaged, or if the coil shows signs of overheating, fuel
preliminary fuel adjustment.
saturation, or other damage.
(6) Clean the groove that retains the preformed
(6) Discard and replace the preformed packings
packing (6) on the carburetor. Install the preformed
and the grommet. The solenoid cap washer may be
packing in the groove, and coat the packing with
reused if it is not damaged, deformed or fuel-soaked.
Aircraft Grease, fuel and oil resistant per Military
d. Reassembly and Installation.
Specification G27617, or equivalent.
(1) Install a new grommet (11, fig. 4-12) over the in-
sulated solenoid coil lead, and slide the grommet into
(7) Install the assembled carburetor in the burner
head and secure with the four screws (24, fig. 4-10) and
the slot in the solenoid cap (10).
lock washers (25).
(2) Install the coil housing (14) and solenoid coil (13)
(8) Coat the male NPT threads of the elbow (23)
on the carburetor (15). Be sure the braided solenoid lead
with Permatex No. 1, or equivalent, and install the
is centered over the tapped hole in the core which
elbow in the top of the carburetor. Slide the tube (22)
protrudes from the side of the carburetor. Install the
over the straight end of the overflow tube (21) and in-
washer (12) and solenoid cap (10), and secure with
stall on the burner head. Connect the other end of the
screw (8) and lock washer (9).
overflow tube to the elbow (23).
(3) Install the fuel heater (7) in the carburetor,
with the leads toward the burner end of the carburetor.
(9) Coat the male NPT threads of the elbow (15)
with Permatex No. 1, or equivalent, and install in the
(4) Install the preheat thermostat (5) on the car-
carburetor fuel inlet. Connect the fuel tube (14) to the
buretor and secure with the two screws (3) and lock
elbow.
washers (4).
(10) Install the top and side cover panels. Connect
(5) Install a new preformed packing (2) in the
the fuel supply and power plug, start the heater, and
groove on the fuel adjustment needle (1). Apply a few
check operation. Adjust the fuel adjustment needle.
small drops of Eastman No. 910 adhesive, or equivalent,
Section IX. MAINTENANCE OF ELECTRICAL SYSTEM
4-25. Description of Electrical System
4-24. Description.
Operation.
a. Thermocouple. The thermocouple helps to control
heater operation. Once the burner is lighted, heat from
a. Startup.
the burning fuel heats the end of the thermocouple
(1) When the operator turns the ON-OFF switch S1
which projects into the heat exchanger. This heat
(fig. 1-3) to ON, and if the room thermostat contacts are
generates a small current in the thermocouple. The
closed, current flows through control relay K2 to the
glow plug G1 to heat the combustion chamber, and to
other end of the thermocouple is connected to the ther-
mocouple relay (flame switch S3), and this small cur-
timer heater S7 to begin the time delay cycle.
(2) With S1 closed, power is also available at fuel
rent which is generated energizes the relay coil, closing
preheat thermostat S6 to heat the carburetor body if
the relay contacts.
b. Room Thermostat. The room thermostat mounts
the ambient temperature is below 40F (4C).
b. Transition.
on a wall in the heated enclosure. It is connected to the
heater by a three-wire cable which plugs into the front
(1) The time delay switch S8 is open at room tem-
of the heater. The thermostat senses the temperature
perature. Heat from timer heater S7 causes switch S8
to close after a delay of 30 to 35 seconds at room tem-
of the air in the enclosure and turns the heater on and
perature to as long as 2.5 minutes at -50F (-45C).
off, as long as the ON-OFF switch is on and the heater
is supplied with fuel.
(2) When the time delay switch closes, it sends cur-
c. Blower Motor. The blower motor provides both
rent to ignition power supply T1 to start the spark in
combustion air to support the burning of fuel in the
the igniter, and to the fuel pump L2. Solenoid L1 is also
burner head, and ventilation air to heat the enclosure.
energized and it opens a valve to start the flow of fuel
The motor has an internally mounted thermal overload
into the burner head.
protector to shut it off in the event of overheating, You
(3) The time delay switch S8 energizes the blower
can replace the motor brushes without removing the
motor B1 through the control relay jumper wire to start
motor from the heater case.
the flow of combustion air into the burner head.
4-19
