TM 9-2350-256-34-1
3. Energize the power supply and turn on
switch A. Adjust power supply to read 24 volts at
V,.
4. Ground the voltage limiter on test
through its mounting bracket. Clip switch B to the
flag terminal.
5. Turn on switch B and observe the
volage on meter V2. The voltage must be 10.5 volts
minimum to 11.5 volts maximum.
NOTE
The voltage limiter must act instantly to
control the voltage at meter V2 and must
remain steady at the control point. If the
unit is left energized for longer than 60
seconds, a further decline in control
voltage may be observed. This is not
cause for rejection.
6. If the voltage does not fall within
specifications, or if control is erratic or intermitent,
voltage limiter must be replaced.
7. Turn off power supply and switches A
and B. Remove voltage limiter from test equipment
and install voltage limiter at reassembly.
(e) Test diode assembly as follows:
1. Identify the three diode assembly leads:
a. Lead marked 4 with connects to ter-
minal 4 on terminal strip mounted on electrical inlet
assembly.
b. Lead marked GRD which connects to
motor housing to ground the diode assembly.
c. Unmarked lead which connects to one
side of resistor.
2. Use an ohmmeter or ohms test function
of a multitester. Touch one test probe to the ter-
minal on the diode assembly. Touch the other test
probe to the No. 4 lead terminal. Note the meter
reading. Reverse the polarity of the test probes and
note the meter reading. Resistance must be very
high with one polarity and zero or very low with the
other polarity.
3. Repeat this test with the unmarked lead.
Results must be the same.
4. To test the ground diode, touch one test
lead to the mounting leg of the diode assembly.
Touch the other test probe to the GRD lead ter-
minal. Note the meter reading. Reverse the polarity
of the test probes and note the meter reading.
Resistance must be very high with one polarity and
zero or very low with the other polarity.
5. If readings are high or low in both direc-
tions for one or more of the diode assembly leads,
replace the entire diode assembly. Diodes are not
serviceable individually.
(2) Electrical inlet assembly (fig. 2-10.2). In-
spect the electrical inlet assembly (36) for cracks,
damaged connector, chipped or broken terminal
strip,
missing screws, and defective fasteners;
replace a defective electrical inlet assembly.
(3) Igniter (fig. 3-10.2)
(a) With the igniter leads still connected to
the ignition control and ground, reconnect the elec-
trical cable to the receptacle and disconnect the fuel
shutoff solenoid lead from terminal 30 on the
overheat switch (to shut off fuel and avoid flooding
the burner), then move the control switch to START
and hold it until igniter element glows.
CAUTION
If the igniter has been removed from the
heater it must be tested at 10 volts or
less. Voltage in excess of 10 volts will
destroy the igniter in a short time.
(b) Carefully examine the glowing igniter. An
igniter which has hot spots, uneven coil spacing, and
hot and cool coils, has deteriorated significantly
from its origiaal condition and should be replaced.
(c) Ignition wick inspection.
1. With the igniter removed, look into the
igniter tube and inspect the condition of the ignition
wick (5, fig. 3–10.5) using a flashlight if necessary.
The wick should be dry, unbroken, and white or
nearly white. The strands should be about 1/16 inch
thick.
2. If the strands are thin or broken, remove
the burner assembly as described in paragraph
3-33c(8) and repair or replace the burner.
3. If the wick is wet, the burner is flooded.
Disconnect the shutoff solenoid lead at terminal 30
on the overheat switch. Reinstall the igniter and
hold the control switch in the START position for
several minutes. A white, smoke-like fuel vapor will
flow from the exhaust until the heater lights. When
the heater lights, reconnect the shut-off solenoid
lead to terminal 30.
(4) Flame detector switch (fig. 3-10.7).
Change 2
3-18.13
