TM 5-4520-240-18
c. Unscrew the connector bolt (4) and disconnect the
thermocouple lead from the thermocouple relay (7).
Remove the cover from the relay, and tag and discon-
nect the electrical leads from the relay. Remove the
four screws (5) and lock washers (6), and remove the
thermocouple relay from the housing.
d. Disconnect the orange and green leads from the
overheat thermostat (10). Remove the two screws (8)
and lock washers (9), and remove the overheat ther-
mostat from the bracket on the heat exchanger.
e. Tag and disconnect the electrical leads from the
terminal block (17) and from the tabs (12, 13, and 14) on
the terminal board. Remove the two screws (15) and
lock washers (16) and remove the terminal block from
the bottom of the heater housing.
f. Remove the wiring harness (18) if the wires are
frayed, burned, or have defective insulation.
7-3. Cleaning and Inspection.
WARNING
Clean parts in a well-ventilated area.
Figure 7-2. Control relay terminal identification.
Avoid inhalation of solvent fumes and
prolonged exposure of skin to cleaning
solvent. Wash exposed skin
thoroughly. Dry cleaning solvent (fed.
spec. P-D-680) used to clean parts is
potentially dangerous to personnel
and property. Do not use near open
flame or excessive heat. Flash point of
solvent is 100F (38C).
Wipe the components with a clean, dry cloth.
Dampen-the cloth with dry cleaning solvent (fed. spec.
P-D-680) if necessary to remove greasy or gummy
deposits. Do not saturate the electrical components.
CAUTION
The control relay is designed for 28-
volt operation only. Voltage in excess
of 28 volts may destroy the relay coil
(terminals Xl and X2).
NOTE
The control relay must be disconnected from the
●
heater circuits before performing continuity tests.
Alternate circuit paths within the heater will confuse
the test results..
●
b. Replace the control relay (3, fig. 7-1) if the case is
damaged, or if the relay shows signs of overheating or
7-4. Installation.
arcing. Test the resistance of the relay coil with an
ohmmeter. The resistance across terminals X1 and X2
hewn in fig. 7-2) must be 300 30 ohms. There
removal and disassembly procedure. Refer to figure 7-1.
must be continuity only between terminals B2 and B3,
and between A2 and A3, but no continuity across B1
and B2 or across A1 and A2. Replace the relay if it does
not operate as specified.
7-3
