TM 5-4520-240-14
CHAPTER 6
REPAIR OF CONTROL PANEL
6-1. Description.
(5) The RESET switch S2 is normally closed. If the
The following control panel components help control
burner does not ignite, the timer heater will continue to
heater operation:
heat the RESET switch to its opening point. When the
a. Time Delay Assembly. The time delay assembly
RESET switch opens, it shuts off all power to the
heater. The RESET switch requires manual reset,
consists of the timer heater S7 (fig. 1-3), RESET switch
b. Receptacles. The THERMO and POWER recepta-
S2, and the time delay switch S8.
cles are mounted on the control panel to provide con-
(1) The timer heater is energized when the ON-
nections to the room thermostat and to the 28 vdc
OFF switch S1 is turned on, and it heats both the time
power source to operate the heater.
d e l a y switch and the RESET switch.
(2) The time delay switch S8 is normally open, un-
6-2. Removal and Disassembly.
til heat from the timer heater S7 closes it. The time re-
WARNING
quired for the timer heater to trip the time delay switch
T h e ignition system of this space
is longer than the time required by the glow plug to
heater contains dangerous voltages
preheat the burner head to ensure rapid fuel ignition.
w h i c h can cause severe electrical
(3) When the time delay switch finally closes from
shock. Be sure to disconnect the power
the heat of the timer heater S7, it energizes the ignition
plug before repairing the heater.
power supply T1 and the fuel pump L2, starting igni-
tion, fuel flow to the burner head, and the blower
a. Disconnect the power and thermostat plugs and
motor.
remove the top and side cover panels for access to the
(4) If ignition proceeds normally, the contacts of
terminal block strip.
the thermocouple relay (flame switch) S3 close, energiz-
b. Remove the five screws (1, fig. 6-1) and lock
ing the control relay K2. This disconnects the timer
washers (2) securing the control panel to the heater
heater, allowing it to cool down, and bypasses the time
case. Pull out the control panel as far as wires will per-
mit.
delay switch.
6-1
