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 22 of 288
TM 9-2540-207-14&P
1-4
1.2.6 Ventilation Air
Ventilation air is drawn from within the vehicle at the Heater Inlet by a high flow Vent Fan.
The
vent air stream is heated as it flows past the Burner and the Heat Exchanger before it is
discharged out of the heater outlet.
In high heat mode the temperature of the outlet air is about 250°F higher than the inlet air.
For
example, if the inlet air is -40°F, then the outlet air will be about 210°F.
In low heat mode the
vent air flow remains the same, but the outlet air temperature is about 125°F higher than the
inlet air.
The amount of heat produced will begin to be automatically reduced if the outlet air temperature
exceeds 325°F.
If the outlet air temperature exceeds 345°F, the heater will force a shut down,
and enter purge mode.
The heated outlet air may be discharged into a duct that distributes the heated air throughout
the vehicle.
Such an air duct should be 8" inside diameter, and be rated for 350°F under
continuous operation.
The duct must allow unobstructed air flow.
Note: The ducting should be directed away from walls or obstructions to
allow clear re-circulation of vent air.
1.2.7 Exhaust
The exhaust temperature of the heater always exceeds 500°F in run mode and can reach
temperatures as high as 1,300°F.
The Heater
Exhaust Tube connects to a 2" inside diameter
duct.
The duct must be rated for at least 1,100°F continuous operation, be leak tight, and
secured from movement.
1.2.8 Enclosure
Two semi-circular shells, top and bottom, are used to enclose the heater. A seam on each side
of the enclosure is used to minimize ventilation air leakage and maximize structural strength.
A
Top Housing protrudes from the Top Shell of the heater.
This Top Housing contains most of the
fuel system, combustion air system and diagnostic display components.
The Top Housing can
be accessed directly by removing the Top Cover.
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