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TM 5-4120-377-14
Table 4-2. TROUBLESHOOTING (Cont.)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
7. NO HEAT IN EITHER HI HEAT OR LO HEAT MODE.
Step 1. Check for loose or damaged electrical connectors, or damaged wires in wiring harnesses.
Disconnect input power before performing internal electrical troubleshooting.
Voltages used can be deadly.
Tighten or replace loose or damaged connectors or repair damaged wires.
Step 2. Check operation of heater thermostat (S4).
Test thermostat. (See para 4-60.) Replace thermostat if defective.
Step 3. Check operation of mode selector switch (S1).
Test switch. (See para 4-40.) Replace switch if defective.
8. HEAT IN HI HEAT MODE, BUT NOT IN LO HEAT MODE.
Step 1. Check for loose or damaged electrical connectors, or damaged wires in wiring harnesses.
Disconnect input power before performing internal electrical troubleshooting.
Voltages used can be deadly.
Tighten or replace loose or damaged connectors, or repair damaged wires.
Step 2. Check operation of heater relay (K2).
Test relay. (See para 4-56.) Replace relay if defective.
Step 3. Check operation of Temperature control thermostat (S2).
a. Inspect sensing bulb and capillary for damage or leakage. (See para 4-39.) Replace
entire control if bulb is damaged or leaking.
b. Test switch in Temperature control thermostat. (See para 4-39.) Replace entire control, if
defective.
Step 4. Check operation of mode selector switch (S1).
Test switch. (See para 4-40.) Replace switch if defective.
4-49
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