TM 5-4520-241-14
CHAPTER 6
REPAIR OF CONTROL BOX ASSEMBLY
6-1.
DESCRIPTION.
The control box houses the following components which control heater operation. Only the wiring harness and time
delay assembly require maintenance at the direct support level.
a. Room Thermostat Receptacle. The room thermostat receptacle is a military standard three-wire receptacle for
connecting the cable to the room thermostat into the heater control circuits.
b. HEATER-OFF-FAN Switch. The HEATER-OFF-FAN switch maintains the heater in the HEATER or FAN mode,
or deenergizes all components except the circuit breaker.
c. Wiring Harness. The wiring harness connects the electrical circuits inside the heater case to the control
components in the control box.
d. PC Board and Transistor. The PC board and transistor are the electrical components which convert the time
delay transformer output to DC and then energize the components in the time delay assembly.
e. Time Delay Assembly. The time delay assembly provides a time delay sufficient for the heater to establish proper
combustion. A thermistor in the bimetallic/sensor compensates for the wide range of voltages which may be encountered
over the entire range of starting temperatures. When the flame switch senses proper combustion temperatures in the
heat exchanger, it throws to normal operation and deenergizes the time delay assembly.
6-2.
CONTROL BOX WIRING HARNESS.
WARNING
This space heater contains dangerous voltages which can cause severe electrical
shock. Be sure to disconnect the power plug before repairing the heater.
a. Disassembly.
(1) Remove the room thermostat receptacle (1, fig. 6-1) from the control box by removing four screws, lock
washers, and nuts.
(2) Remove the two green leads (2) from the grounding screw. Remove clamp (3) by removing the center screw
on the control box hinge.
6-1
