TM 9-4520-271-14
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ELECTRICAL SYSTEM
Continued
When MODE SWITCH S1 is set to HEAT AUTO MODE, remote thermostat S6 controls the burner heat output from
35 F to 85 F (2 C to 29 C). The burner will cycle to the temperature setting on remote thermostat S6 unless the output
exceeds 160 F (71 C). When the temperature exceeds 160 F (71 C), discharge air thermostat S3 shuts off the burner
until the outlet temperature is below 130F (54 C).
When MODE SWITCH S1 is set to HEAT MANUAL MODE, remote thermostat S6 is bypassed and the burner is on
continuously unless the outlet temperature exceeds 160 F (71 C). When the outlet temperature exceeds 160 F (71 C),
discharge air thermostat S3 shuts off the burner until the outlet temperature is below 130 F (54 C). When the outlet air
temperature exceeds 200 F (93 C), overheat thermostat S2 shuts down the burner but the ventilation air fan and the
combustion air fan continue to operate. HIGH TEMP indicator DS2 will light. Flame detector D1 will sense no flame
and FLAME OUT indicator DS3 will light.
FUEL SYSTEM
The fuel system incorporates a 14 gallon (53L) internal fuel tank. Fuel transfer valve V1 enables ASH operation from the
internal fuel tank or from an external fuel source using a 25 foot (7.62m) fuel hose.
Purge System
The purge system enables the operator to purge air from the fuel system before initial startup of the ASH. Purging is also
required when operating from an external fuel source or after the fuel system has been allowed to run dry.
CAUTION
Do not operate the ASH without fuel. Operation without fuel will result in damage to the fuel pump.
The INTERNAL TANK/EXTERNAL TANK selector valve must be fully positioned to either setting.
Any selector valve setting between INTERNAL TANK and EXTERNAL TANK may result in fuel
starvation and damage to the fuel pump.
The fuel system must be purged daily, even when the external fuel tank is being used or the ASH is in
the ventilation mode or the fuel pump may be damaged.
The fuel system is purged by turning MODE SWITCH S1 to the VENT position and holding fuel PURGE SWITCH S4
to the up position until the fuel pressure gage indicates greater than zero. When fuel PURGE SWITCH S4 is released,
the pressure must be greater than 10 psi (69 kPa).
If the fuel pressure is not greater than 10 psi (69 kPa), purging must be continued until the proper pressure is obtained.
Priming the fuel system at extremely low ambient temperatures with the correct fuels presents no problems, except that it
takes slightly longer due to the greater restriction of cold fuel circulating through the filter.
Ventilation Mode
In the ventilation mode, fuel is drawn through the low pressure filter by the fuel pump. The fuel is then pumped through
two-way fuel solenoid valve L1 to the three-way purge solenoid valve L2. Since purge solenoid valve L2 is not
energized, fuel passes through purge solenoid valve L2 and returns to the inlet side of the fuel pump. If purge solenoid
valve L2 is energized, the ASH will operate as described in the Purge System subparagraph above.
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