T M 1 0 - 4 6 1 0 - 2 3 2 - 1 2
Table 4-2. Unit Troubleshooting Guide (Continued)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
(a) If there is power but the preheater does not warm up, replace the preheat cartridge (para. 4-60).
(b) If there is no power, disconnect the heater power cable and check continuity from the heater
terminal T8 back to the heater control box terminal T8 and through the preheat switch.
Tighten any loose wires.
(c) Replace the heater if the preceeding steps have not located the problem (para. 4-60).
Step 6. Check for 24-28 VDC at the heater terminal T5 to terminal T1.
(a) Replace the ignition pack assembly if there is voltage present at the terminals and there is a
weak or no spark from the ignition pack (para. 4-60).
(b) Replace the heater if there is no voltage at the terminals (para. 4-60).
Step 7. Remove the fuel bowl from the fuel pump strainer and check that it is clean.
Clean the screen if dirty and reinstall. Fill fuel bowl with clean fuel.
Step 8. Check the fuel pump suction lines for tightness and damage.
Replace/repair the lines as necessary (para. 4-61).
Step 9. Remove the fuel line from the bottom of the heater and place its end in a container. Toggle the START
switch to the START position and watch if fuel comes out of the line.
If fuel comes out the fuel line, install a fuel pump test gage on the pump and check pressure. It
should be 4 psig (28 kPa). Replace the fuel pump if it is not 4 psi (28 kPa) (para. 4-61).
Step 10. Disconnect the fuel pump electrical connector and check for 24-28 VDC between the center pin of
the connector and ground when the START switch is toggled to start.
(a) If voltage is present, replace the fuel pump (para. 4-61).
(b) If voltage is not present, replace the fuel pump harness cable (para. 4-60).
3. Diesel fuel heater has excessive backfiring or popping.
Step 1.
Step 2.
Step 3.
Step 4.
Step 5.
Check fuel for water.
If water is present in the fuel, change fuel or follow Army SOP for water in fuel problems.
Disconnect the electrical connector for the heater (P/J4 for heater No. 1 and P/J5 or heater No. 2).
Check for 28 VDC (24 VDC minimum) across the A and B pins of the J (female) connector.
(a) If voltage is not resent, refer to power supply troubleshooting.
(b) If the voltage is less than 24 VDC, notify direct support maintenance to troubleshoot power
supply.
Check the carburetor fuel solenoids. Dirt in the solenoid will cause an uneven flow of fuel and backfir-
ing upon recycling.
Clean as needed (para. 4-61).
Check the ignition pack assembly and igniter for operation.
Refer to heater runs but no combustion troubleshooting for test procedures (malfunction 2).
Carefully check fuel control setting. Remove the heater cover. The adjusting needle is located just
above the preheat cartridge on the carburetor body.
Carburetor adjustment must be made while the heater is running. If the carburetor fuel needle is
seated so that insufficient fuel is allowed to pass to start combustion, back if off one turn and then
start the heater. Adjust the setting of the fuel needle after the heater is operational. Turning the
needle clockwise will lean out the fuel mixture. When properly adjusted, the heater will burn evenly
and smoothly with no smoke in the exhaust. The end of the combustion chamber should also turn a
red color when the adjustment is correct.
4. Diesel fuel heater fan fails to go to high speed during burning cycle.
Step 1. Disconnect the electrical connector for the heater (P/J4 for heater No. 1 and P/J5 for heater No. 2).
Check for 28 VDC (24 VDC minimum) across the A and B pins of the J (female) connector.
(a) If voltage is not resent, refer to power supply troubleshooting.
(b) If the voltage is less than 24 VDC, notify direct support maintenance to troubleshoot power
supply.
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