TM 9-4120-357-14
Section XIII. MAINTENANCE OF HEATER ASSEMBLY
4-40. General.
The heater assembly consists of six w-shaped rod-type heating elements. (See figure 4-14.) Three of the elements (10)
are energized when the selector switch is set at lo heat, through a heater relay and an over-temperature thermostat (7).
The remaining three elements are energized when the selector switch is set on hi heat. The lo heat elements are con-
trolled by the temperature control thermostat on the control panel when the selector switch (also on the control panel) is
set at lo heat. The hi heat elements are not thermostatically controlled. The elements are located across the width of the
air conditioner just behind the evaporator coil, and are separated from the blower plenum by a perforated diffusing baffle.
4-41. Maintenance of Heating Elements.
a. Access. Obtain access to
the heating elements as
directed in
the following steps:
(1) Remove 16 screws and washers from the evaporator discharge grille. Remove the grille.
(2) Remove 31 screws from the top and rear flange of the top panel. Remove or push back the top panel.
WARNING
Disconnect power from the air conditioner before performing maintenance work
on the electrical system. The voltages used can be lethal.
b. Inspection/Test. Without removing the elements, disconnect wires from the each element in turn and check
continuity. Use an ohmmeter or continuity tester at the terminals of each element, and make sure that continuity exists.
No continuity should exist between, and make element and around. Visually inspect elements for obvious damage. Re-
place any element(s) that do not indicate continuity.
c. Removal. To remove a heating element, disconnect electrical leads, unscrew two panel fastener screws captive
on the channel from the heater support. Remove element (10) by pulling straight up.
d. Installation. Insert heating element (10) straight down into the space between the heater support assembly (8)
and the evaporator coil. Place heater support (9), with notches mating with heating elements (10), and secure with two
captive panel fastener screws. Connect electrical leads to terminals of element.
e. Assembly. Assemble the air conditioner as follows:
(1) Position the top panel on the air conditioner. Secure it with 31 screws through the top and rear flange.
(2) Position the evaporator air discharge grille on the front of the air conditioner. Secure it with 16 screws and
washers.
4-42. Maintenance of Heater Thermostatic Switch.
The heater thermostatic switch (7, Figure 4-14) acts to protect the heating elements against burnout. This condition can
occur when the temperature control thermostat on the control panel is set at maximum increase for an extended period
while airflow is obstructed or the evaporator blower is not operating. Perform maintenance on the heater thermostatic
switch as follows:
a. Access. Obtain access to the heater thermostatic switch in accordance with the following procedure:
(1) Remove 16 screws and washers from the evaporator discharge grille. Remove the grille.
(2) Remove 31 screws from the top and rear flange of the top panel. Remove or push back the panel.
4-46