Sterling TD - Manual (Page 25)

25
OPERATION
TUBULAR DUCT FURNACE DIRECT SPARK IGNITION
EXPLANATION OF CONTROLS:
1. The duct furnace is equipped with a power vent
system that consists of a power vent motor and
blower, pressure switch, and sealed fl ue collector in
place of a conventional gravity vent draft diverter.
2. The power vent motor is energized by the room
thermostat through the integrated control board when
a demand for heat is sensed. The pressure switch
measures the flow through the vent system and
energizes the direct spark ignition system, beginning
the pre-purge timing when the fl ow is correct.
The pressure switch MUST NOT be
bypassed. The duct furnace MUST NOT be fi red
unless the power vent system is operating. An
unsafe condition could result.
3. The direct spark ignition system consists of an
integrated control board, a spark ignitor, a fl ame
sensor, and a gas valve. When the pre-purge period
ends, the direct spark ignition system is energized,
and the gas valve opens to supply gas to the burners.
When the thermostat is satisfi ed, the vent system is
de-energized and the gas valve closes to stop the
fl ow of gas to the unit. (See Figure 12.)
4. The high limit switch interrupts the fl ow of electric
current to the control board if the duct furnace
becomes overheated, interrupting the fl ow of gas to
the gas valve. The duct furnace will begin a post-
purge period. When the post-purge period ends, the
power vent motor is de-energized.
5. Once the thermostat is satisfi ed, the duct furnace will
begin a post-purge period. When the post-purge
period ends, the power vent motor is de-energized.
6. The wall thermostat, supplied optionally, is a
temperature sensitive switch that operates the power
vent and direct spark ignition system to control the
temperature of the space being heated.The thermostat
must be mounted on a vertical, vibration-free surface
free of air currents and in accordance with the
furnished instructions (also refer to Electrical
Connections section of this manual).
START-UP (Also refer to lighting instruction plate
equipped on the unit)
1. Open the manual gas valve in the gas supply line to
the duct furnace. Loosen the union in the gas line to
purge it of air. Tighten the union and check for leaks.
Never use an open fl ame to detect
gas leaks. Explosive conditions may exist which
could result in personal injury or death.
2. Open the supply gas valve on the duct furnace.
3. Turn ON the electrical power.
4. Turn on system fan (provided by others).
NOTICE: Failure to turn on system fan when duct
furnace is running will cause the unit to trip on high
limit. This may result in damage to the duct furnace
and heat exchanger.
5. The unit should be under the control of the thermostat.
Turn the thermostat to the highest point and
determine that the power vent motor starts and the
burners ignite. Turn the thermostat to the lowest point
and determine that the power vent motor shuts off
and the burners are extinguished.
6. Turn the thermostat to the desired position.
7. See Gas Input Rate section.
SHUT DOWN
1. Turn the supply gas valve selector to the OFF position.
2. Turn off the electricity.
3. To relight, follow “START-UP” instructions.
See Figures 12 and 13 for parts identifi cation.
Figure 12 - Direct Spark Ignition System,
Tubular Duct Furnace
ORIFICE
BURNER BRACKET
D9375
GAS VALVE
SPARK IGNITOR
FLAME SENSOR
BURNER
MANIFOLD
D9375