TM-9-2540-207-14-P
HEATER, VEHICULAR COMPARTMENT, MODEL: A20
TECHNICAL MANUAL; OPERATOR, FIELD, AND SUSTAINMENT MAINTENANCE MANUAL INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST
JULY 2007
TM-9-2540-207-14-P - Page 20 of 288
TM 9-2540-207-14&P
1-2
1.2
Principles of Operation
1.2.1 Electronic Controller
The heater operation is controlled by an electronic micro controller (Programmed Controller)
supported by hardware and software. The hardware is based on a microprocessor and power
handling circuits that direct signals and power to and from all inputs and outputs. The
microprocessor is programmed with software to receive input data, perform calculations, and
send output signals and data. The software is a unique set of instructions that the
microprocessor executes to perform calculations, store information, read input data, control
output signals, and measure time.
Programmed Controller inputs are required to power the electronic controller board, and to
provide input data to the micro-processor.
Programmed Controller outputs are used to operate
the heater assemblies for ignition, air delivery, fuel delivery, safety, and self diagnosis.
1.2.2 Burner
The Burner uses a fuel spinner that can atomize all types of diesel fuel; a sheathed glow plug
Ignitor is used to ignite the fuel; a Burner Temperature Sensor (Thermocouple) in the Burner,
and another in the Heat Exchanger exhaust monitor operating temperatures.
During the heater
start up, the Ignitor is energized, and a small amount of fuel is then introduced (approximately
one minute after the Ignitor is turned on).
When ignition of the fuel happens, the Programmed
Controller will sense a rapid Burner temperature increase.
When this temperature increase is
detected, the Programmed Controller will output signals to deliver more combustion air and fuel
to the primary burner.
Fuel is pumped through a spinning shaft spraying the fuel into a mist,
which is then ignited. As the Burner temperature steadily increases, so does the air and fuel
delivery rates.
If at any time during this ramp-up phase a flame-out should occur, the
Programmed Controller will reduce air and fuel delivery until the Burner temperature sensor
detects that ignition has been re-established.
During start up, about 10 to 20 percent of the normal fuel quantity is delivered for ignition
purposes.
This ensures a safely controlled start and prevents the Burner from flooding with fuel.
This allows the operator to restart the heater without excessive fuel build up inside the Burner
and the Heat Exchanger.
Note: The operator should not try more than three (3) consecutive start
attempts without referring to the Diagnostic Display code displayed, and
commencing Troubleshooting and any recommended maintenance actions.
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