TM 10-4610-232-12
Table 4-2. Unit Troubleshooting Guide (Continued)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
1. Diesel fuel heater does not start (motor fails to run) (Reference Schematic Diagram FO-1, Sheet 11, schematic
lines 1131-1135).
Step 1.
Step 2.
Step 3
Step 4.
Step 5.
Step 6.
Disconnect the electrical connector for the heater (P/J4 for heater No. 1 and P/J5 (Reference lnter-
connection Diagram FO-2, Sheet 14) for heater No. 2). Check for 28 VDC (24 VDC minimum) across
the A and B pins of the J (female) connector.
It voltage is not present, refer to power supply troubleshooting.
Remove the cover on the heater control box. Be careful that any wire connections are not touching the
metal enclosure. Reconnect the heater connnector that was disconnected in step 1. Check for 28 VDC
(24 minimum) across terminal 1 (negative) and heater circuit breaker CB-1 (positive) (Reference ln-
terconnection Diagram FO-2, Sheet 10).
If voltage is not resent, replace the heater cable and connector (P4 or P5) (para. 4-60).
Check for 24-28 VDC across terminal 1 and CB-1 (red wire).
If voltage is not present, replace the circuit breaker CB-1 (para. 4-60).
Remove the heater cover. Check for 24-28 VDC across the heater terminals T2 and T1 and between
T4 and T1 when the START-RUN-OFF switch on the heater control box is toggled to START.
If voltage is present and the motor does not run, replace the heater (para. 4-60).
Disconnect the connector on the bottom of the heater. Check for 24-28 VDC across the jack (female)
pins B and A and between D and A when the START switch is toggled to START.
If voltage is present, replace the heater electrical connector cable assembly (para. 4-60).
Check for 24-28 VDC at terminals T2 and T1 and between T4 and T1 in the heater control box with the
START switch toggled to START.
(a) If voltage is present, replace the electrical cable from the control box to the heater (para.
(b) If voltage is not present, replace the heater control box (para. 4-60).
2. Diesel fuel heater motor runs but there is no combustion.
Step 1.
Step 2.
Step 3.
Step 4.
Step 5.
Check for fuel at the float bowl (para. 4-60). Remove the 1/8 NPT pipe plug in side of float bowl and
gently depress the float. If fuel is present, it will show on the object used to depress the float and buoy-
ancy can be felt.
If there is no fuel, go to step 8.
Check for hold-fire thermostat control assembly maladjustment.
Refer to maintenance procedures for adjustment (para. 4-60).
W A R N I N G
If the high tension lead is disconnected from the igniter for any reason, DO NOT ener-
gize the unit without first providing a discharge gap of 1/8 inch or less from the high
tension lead to the grounded igniter. With a larger gap, electrical potential can build
up to a point which can cause an insulation breakdown in the ignition pack assembly
or in the high tension lead. The same also applies if the high tension lead is attached
to the igniter with the igniter removed from the unit. Provide a gap of 1/8 inch or less
Check for spark by holding an insulated-handle screwdriver with the shaft grounded and the tip ap-
proximately 1/8 inch away from the high tension lug of the ignition pack assembly. There should be a
continuous strong yellowish spark.
If no spark or a weak spark is produced, go to step 7.
Remove and check the igniter. There should no heavy deposits and the electrode should be cen-
tered. Visually check operation with the igniter removed-from the burner head, but connected to the
high tension lead. Disconnect the fuel pump electrical connector at the fuel pump and lay t he igniter on
the heater case to check for spark. The igniter must be grounded when testing.
Replace the igniter if it has heavy deposits or the center electrode is damaged or if there is no spark
(para. 4-60).
Remove the preheat cartridge from the carburetor. Lay it on the heater case so it is rounded and
toggle the cheat switch on. The cartridge should start to heat up. Check for 24-28 VDC across heat-
er terminal T8 and T1.
Change 1
4-69
4-60).
here also.
