TM 5-3810-307-24-1-2
THEORY OF OPERATION
Operate the coolant heater manually by depressing the Heater "On"
pushbutton on the seven day
timer (18) located in the cab. The following sequence occurs:
a.
Coolant heater control unit (4) performs a system readiness check lasting one to three
seconds. The control unit verifies that the flame sensor (2), temperature sensor (6), and
overheat sensor (9), etc., are operational.
b.
Water pump (10) starts and circulates engine coolant through the water jacket
surrounding the heat exchanger (8).
c.
The combustion air blower motor (1) starts.
d.
Glow pin (5) begins a pre-heat sequence that lasts from 20 to 50 seconds.
e.
Fuel metering pump (13) delivers fuel to the combustion chamber (3) at the end of the
glow pin pre-heat sequence while the combustion air blower motor (1) ramps up
gradually to full air flow.
f.
Fuel is ignited in the combustion chamber (3). Upon fuel ignition, the flame sensor (2)
signals the control unit that ignition has occurred and the control unit shuts off the glow
pin (5) (ignition time: 1-1/2 to 2 minutes).
NOTE
If the coolant heater fails to start on the first try, the control unit (4) will
automatically attempt a second start which includes a second pre-heat
sequence (50 seconds). If the heater does not start after the second
attempt, the heater and control unit will shut down completely.
FIRST TIME STARTUP. When starting the coolant heater for the first
time, the system may require several start up attempts in order to self
prime the fuel system.
Fuel ignition occurs and is verified. The following sequence occurs:
a.
Coolant heater runs in full heat mode and the coolant temperature is monitored in the
heat exchanger (8) via temperature sensor (6).
b.
When the engine coolant reaches 162 F (72 C), the coolant heater control unit (4) will
cycle the coolant heater up and down between high, medium, and low.
c.
The coolant heater control unit (4) shuts off the coolant heater when the engine coolant
temperature reaches 185 F (85 C).
d.
The water pump (10) continues to circulate engine coolant while the temperature sensor
(6) monitors the temperature. The coolant heater control unit (4) will automatically re-
start the coolant heater if the coolant temperature drops to 154 F (68 C).
