TM 5-4520-256-14
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
If fuel pressure rises, unit is functional.
If fuel pressure fails to rise, proceed to step 4.
Step 4.
With (S1) in VENT mode, check that fuel pump is operating.
If motor shaft (pump side) or coupling is broken, notify Intermediate Direct Support Maintenance.
If pump is operating, proceed to step 5.
Step 5.
Check for clogged fuel filter.
If fuel filter is clogged, service fuel filter (para 3-35).
If fuel filter is not clogged, proceed to step 6.
Step 6.
With (S1) in VENT mode, check operation of solenoid valve L2.
If fuel pressure lowers with switch S7 ON and rises to 10 to 20 PSI with S7 OFF, L2 is operating properly,
proceed to step 7.
If L2 is not operating properly, replace valve (para 3-34).
Step 7.
Check for 120(±10) Vac between TB1-9 and TB1-8 with switch (S1) set to HEAT mode.
If voltage is present, proceed to step 8.
If voltage is not present, proceed to step 9.
Step 8.
Check that solenoid valve L1 has operated and is closed.
If valve has not operated when (S1) is set to HEAT mode, replace solenoid valve L1 (para 3-34).
If solenoid valve L1 has operated, and low fuel pressure still exists, replace fuel pump (para 3-24).
Step 9.
Check that both thermostats on the temperature controller are set higher than ambient temperature.
Adjust as necessary and proceed to step 10.
Step 10.
If the fuel pressure still fails to rise when OFF/VENT/HEAT switch (S1) is set to HEAT Mode, replace
combustion control relay (K8) (para 3-17).
3-9
