1-12. ELECTRICAL SYSTEM - continued.
b. Heating Mode. - Continued.
(2) Temperature Controller Circuits. The components comprising the temperature controller circuits are the return
air thermostat. discharge air thermostat. and temperature controller. Both thermostats are adjustable and are
connected in series internally in the controller. Adjustment of these thermostats is accomplished by rotating
knobs on the temperature controller housing. The burner will cycle on either of the two thermostats.
1-13. FUEL SYSTEM. (Refer to Figure 1-7).
a. General. The fuel system is illustrated schematically on figure 1-6. The fuel system incorporates a 26-gallon fuel
tank. A fuel transfer valve is provided to enable operation of the heater from the internal fuel tank or from an external
fuel source. The fuel pump operates when motor B 1 is operating.
b. Purge System. The purge system is provided to enable the operator to purge the unit upon initial startup of the
heater, when operating from an external fuel source. or when attempting to start the unit after the external fuel system
has been allowed to run dry. Priming the fuel system at extremely low ambient temperature with the correct fuels
presents no problems except that it take slightly longer due to the greater restriction of fuel movement by cold fuel
circulating through the filter. Priming the fuel system is done by turning the mode selector switch to the VENT position,
holding switch S7 to the on position until the fuel pressure gage reads greater than zero. When switch S7 is released; the
pressure must be greater than 10 psi. If not, purging must be continued to bleed the fuel system until the pressure is
greater than 10 psi with switch S7 off.
c. Heating Mode. In the heating mode, fuel is drawn through the fuel filter by the fuel pump. Upon thermostat
demand, fuel is supplied to the nozzle at the required set pressure as indicated on the fuel pressure gage. Unused fuel is
bypassed back to the pump through the secondary bypass line. Upon attaining the desired discharge or return air
temperature, solenoid valve L1 will assume the normally open position and all fuel will return to the pump through the
primary bypass line and will be recirculated through the fuel pump.
1-12 Change 3