In the heating modes, fuel flow is the same as during the ventilation mode. Upon heat demand, fuel solenoid valve L1
opens and fuel is supplied to the nozzle at the set pressure. Unused fuel is bypassed back to the pump through the
secondary bypass line. When desired air temperature is reached, overheat thermostat S2 activates, or combustion control
relay K1 activates, closing fuel solenoid valve L1. When fuel solenoid valve L1 is closed, all fuel will return to the pump
through the primary bypass line.
The fuel tank drain provides a means to drain the tank when required.
The fuel tank gage mechanically indicates the level of fuel in the internal fuel tank.
The fuel filler neck provides a means to fill the fuel tank with fuel. A fuel strainer is located inside the neck to trap
foreign objects before they enter the fuel tank. The screen can be removed and cleaned for reuse.
The fuel pressure gage indicates purge and operating fuel pressures.
The airflow system is divided into two separate airflows: combustion airflow and circulating airflow. In circulating
airflow, the air is either ventilated (ambient) air or heated air. Major components include the ventilation air fan, heat
exchanger, burner, and combustion air fan.
Ventilated air is drawn through the return air duct and/or the fresh air damper by the ventilation air fan. The ASH
enclosure becomes pressurized and air moves around the heat exchanger and is discharged through the supply air duct.
Heated air is identical to that described for the ventilation mode, except that the air passing over the heat exchanger is
heated by the heat exchanger and regulated by either the remote control box (auto mode) or the discharge air thermostat
Combustion airflow is provided by the combustion air fan. The airflow is applied to the burner, mixed with vaporized
fuel, and ignited. The resulting hot gases pass through the heat exchanger and exit as exhaust.